Clare - are smaller car tires easier to balance than SUV tires?

[Arlen G. Holder]

Clare - are smaller car tires easier to balance than SUV tires?
<https://i.postimg.cc/kG1M7cLd/mount15.jpg>

A neighbor was in need of tires who knew that I had bought a few extra for
her long ago where they've been sitting outside in the rain & mud for
months waiting for her to need them.
<https://i.postimg.cc/7L8HPbtb/mount16.jpg>

She finally wore through the belts and had to stop over for an "emergency"
tire change, which I did for her, but she was in a rush so we did it in
about 20 minutes from start to finish.

I had to do it so fast that I didn't see the yellow dot until I looked at
this picture, where I mounted the red dot to the valve stem instead of the
yellow dot as you had recommended for when there are no match mounting
marks.

I did statically balance and she reported no vibration whatsoever. I didn't
spend a lot of time cleaning up things so I'm surprised there's no
imbalance given how quickly I did the job for her.

Just wondering if you've found that these tiny 14-inch tires are a piece of
cake compared to the normal truck SUV tires (like the Optimo's that I'm
used to) both in terms of mounting and balancing?

[devnull]

On 6/12/19 1:52 AM, Arlen G. Holder wrote:
> she was in a rush so we did it in
> about 20 minutes from start to finish.

Now that's a quickie!

[Ed Pawlowski]

Yeah, but it was 19 minutes foreplay.

[devnull]

If the nuts are rusty, sometimes you got to heat up the stud to get them off.

[Ed Pawlowski]

Better than having them bleed
https://nypost.com/2019/06/11/florida-woman-squeezed-boyfriends-genitals-until-they-bled-cops/

[Clare Snyder]

Yes and no. The smaller tire has less total mass so a small amount
of weight has more effect than it would on a bigger tire - but it is
not as far from the center (shorter moment arm) so it has less effect.

GOOD tires of any size are easier to ballance than crappy tires. Ealy
Hankooks were a real pain to ballance. Apparentlythey have gotten
better.

[Arlen G. Holder]

On Wed, 12 Jun 2019 21:37:49 -0400, Clare Snyder wrote:

> Yes and no. The smaller tire has less total mass so a small amount
> of weight has more effect than it would on a bigger tire - but it is
> not as far from the center (shorter moment arm) so it has less effect.

Thanks Clare as I never mounted and balanced a tire so fast on purpose, not
even taking time to clean the wheel or even remove the old weights until
AFTER I put it on the static balance stand.

These tires are Lexani LXTR 203 model tires, of size P185/65R14 with load
range 86 and speed range H (traction A, temperature A, and treadwear 500),
where I don't know WHAT specific thing makes these so easy to balance, but
they're so easy that something is very different.

I was surprised that I skipped a bunch of steps, and yet, the wheel _still_
didn't cause any perceptible vibration, according to the driver, even as
it's a front wheel drive vehicle with the tire being the driver side front
tire.

I had told the owner to take it to Costco for the $5 wheel balancing, but
that wasn't even necessary, even as I skipped a bunch of balancing steps.

The old tires on her car were model "Grand Prix" of size P185/65R14 load
range 86 and speed of T (traction A, temperature B, and treadwear 500)
which seem to be wearing on both edges, where here are the front two tires
of this FWD vehicle with the tires set up in the appropriate position.
<https://i.postimg.cc/JzvTyjKg/mount18.jpg>

I had previously replaced her passenger front tire due to this gouge
<https://i.postimg.cc/4dTBPZDQ/mount19.jpg>

Where the driver front tire wore into the steel belts which jutted out
<https://i.postimg.cc/85Bwn9DQ/mount20.jpg>

She needed to be somewhere so I was in such a rush, that I didn't even
_see_ the yellow (weight) dot when I mounted the valve stem to the red
(uniformity) dot:
<https://i.postimg.cc/7L8HPbtb/mount16.jpg>

Where I only noticed the yellow dot when I looked at this picture!
<https://i.postimg.cc/kG1M7cLd/mount15.jpg>

Back to how easy it was to statically balance these tires, not only did
this tiny car have the only four-lug wheel I've ever worked on, but popping
the first bead of this tiny 14-inch P185 tire was so simple that it took
only a couple of pumps and about triple that to break the second bead.

Removing the third bead and fourth bead was, likewise, surprisingly simple.
Popping on the fifth bead was almost entirely done by hand, it was that
easy, where only the sixth bead took any effort whatsoever that required a
force that any teenager could exert.

With two wheel weights already on the rim, and by match mounting the red
dot (I didn't even _see_ that yellow dot until I looked at the picture
afterward), the balance was spot on in the middle of the bubble level.

So I didn't even remove the _old_ wheel weights, which I normally would
have done as part of the wheel prep after breaking the bead and removing
the old tire. I didn't even replace the valve stem, as I recently used up
the four valve stems I had bought after speaking to you about getting the
bolt-in kind so I didn't have any available.

The tires have been waiting for her outside in the mud and rain, so I
simply bounced and blew out the leaves and crud where I would have cleaned
the tires more had I more time, where I might have noticed that yellow dot
which was slightly worn away from being outside all winter.

> GOOD tires of any size are easier to ballance than crappy tires. Ealy
> Hankooks were a real pain to ballance. Apparentlythey have gotten
> better.

Funny you mention the Hankook's where I just snapped this for you!
<https://i.postimg.cc/zGVtXxwK/mount17.jpg>

Those are Hancook Optimo H724 model tires of size P225/75R15, with the load
range of 102 and speed range of S (traction A, temperature B, and treadwear
500), which were MUCH HARDER to mount and dismount and harder to balance
too, it seems.

I'm planning on mounting and balancing them this weekend on an SUV which
keeps wearing out the front tires which I have to get alignment tools to
check the camber mostly since they're wearing on the outside edge.

When I mount those thick-sided Hancooks, on steel wheels, I will mount by
the _yellow_ (minimum weight) dot for the first time, instead of by the red
(maximum runout) dot, as I recall you recommended for when there's no match
mounting mark on the rims.

Thanks for being helpful where you're just about the only guy on this
newsgroup who knows anything about this subject matter, which I greatly
appreciate your advice, and where I try to remember it all over the years,
where I'm starting to lose count of how many tires I've done in the past
five years with the crappy Harbor Freight tools (they work, but they suck).

[Xeno]

You can check the camber all you like but the answer is more likely in
the SAI angles and you will be able to do SFA about that. Quiz the owner
about type of use instead. If it is all city and suburban driving, tyre
wear on the outside of the tread can be considered 100% normal.
Turn the wheels to a high level of lock and the obvious will confront
you. The type of feathering will tell you what the actual cause is.

>
> When I mount those thick-sided Hancooks, on steel wheels, I will mount by
> the _yellow_ (minimum weight) dot for the first time, instead of by the red
> (maximum runout) dot, as I recall you recommended for when there's no match
> mounting mark on the rims.
>
> Thanks for being helpful where you're just about the only guy on this
> newsgroup who knows anything about this subject matter, which I greatly
> appreciate your advice, and where I try to remember it all over the years,
> where I'm starting to lose count of how many tires I've done in the past
> five years with the crappy Harbor Freight tools (they work, but they suck).
>

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

[Clare Snyder]

Running the dang things half flat or cornering like an idiot - - -

>
>Where the driver front tire wore into the steel belts which jutted out
><https://i.postimg.cc/85Bwn9DQ/mount20.jpg>

Driving on tires like that should be criminal

[Arlen G. Holder]

On Thu, 13 Jun 2019 11:45:55 -0400, Clare Snyder wrote:

> Running the dang things half flat or cornering like an idiot

Hi Clare,

Thanks for that advice, as I am "trying" to "read" the story of tires, but
I'm not doing well as most of it is cryptic to me, while it might be
obvious to you - so I appreciate any insight you can give on how you read
tire wear.

I agree with you that it's unusual for a gouge that big that the treads
were visible underneath, as shown below...
<https://i.postimg.cc/hjgtsc3Z/mount21.jpg>
and where the tire finally just deflated in split second while she was
pulling out of her driveway.
<https://i.postimg.cc/4dTBPZDQ/mount19.jpg>

> Driving on tires like that should be criminal

I have two more tires to put on for her for her rears, which are worn more
evenly (she probably doesn't rotate?) so I told her to wait until she
needed them since they are just sitting outside (I moved them into the
garage as they were getting dirty in the rain over the winter).

I have never owned a FWD vehicle so I'm not sure yet how the wear patterns
differ, but this set of tires seems to be worn on both outside edges with
the actual edge being hit the hardest.
<https://i.postimg.cc/RCRdRMWd/mount22.jpg>

[Arlen G. Holder]

On Thu, 13 Jun 2019 17:11:14 +1000, Xeno wrote:

> You can check the camber all you like but the answer is more likely in
> the SAI angles and you will be able to do SFA about that.

Hi Xeno,

Thanks for your purposefully helpful advice on kingpin inclination angle
(aka steering axis inclination), and perhaps included angle, neither of
which have I delved into yet (as I'm starting with camber, which is the
basis for caster calculations, and where toe is relatively simple).
<http://www.valleyofhastings.com/WheelAlignment2.pdf>

Other than Clare, you and maybe one or two other folks here are
knowledgeable in the important details of home alignment checks &
adjustments, where I don't usually disagree with anything you guys say, as
you know more than I do.

We have to remember a home DIY alignment check & adjust is sort of like
doing a DIY tuneup versus a complete engine overhaul
o A DIY caster/camber/toe check/adjust is to a professional alignment
o as a DIY tuneup is to a professional engine blueprinting overhaul

The fact is that the SIA is a "non adujstable" angle:
<https://www.freeasestudyguides.com/included-angle.html>

The fact it's not adjustable means it is in a different category than
o caster
o camber
o toe

While SIA is not normally adjustable, looking this up anyway for more
insight, it seems SIA checks generally simply need yet _another_ magnetic
bubble gauge, much like the camber gauge apparently, but offset by 90
degrees, according to this cite:
o Checking the Steering Axis Inclination Angle
<http://route66hotrodhigh.com/Inclination.html>
Which says:
"To measure steering axis inclination, the method is identical to caster
measurement except that you use the steering axis inclination guage [sic]
which is at a 90 deg angle to the caster gauge. The wheel is turned 20 deg
inward. The steering axis inclination gauge is centered for 0 deg caster.
There is an adjustment screw on the back of the gauge that allows you to
set it for 0 deg. The wheel is then turned to 20 deg outward for a total
movement of 40 degrees. The steering axis inclination angle is read off the
gauge."

The key question is where to get that SIA gauge, which, apparently, can be
replaced with a normal magnetic caster gauge according to this patent:
o Device & method for measuring SAI on a steerable wheel (#4,546,548)
<http://www.freepatentsonline.com/4546548.pdf>

In short, if we're aligning a vehicle that we own and drive often, then we
don't have any reason to suspect SIA changes (which will only occur with
bent or worn parts), and hence, they aren't part of what typically changes
(which is caster, camber, and toe).
<https://www.motor.com/magazinepdfs/062002_05.pdf>

> about type of use instead. If it is all city and suburban driving, tyre
> wear on the outside of the tread can be considered 100% normal.

On this mountain, everyone wears tires sooner than people who drive in
flatland do, where there is just "something" horrific about five miles of
steep driving,

Most seem to wear on the outside edge, which I still haven't figured out
exactly why. The road is about 5 miles at about a 9 percent angle with very
many 180 degree and even 270 degree switchbacks, but the speeds are rather
slow, where the road is too narrow to even have panted centerlines and
where the nominal speed limit for such roads is 25mph.

Given nobody drives 25 mph anywhere, we can figure it's something like 30
mph to 40 mph top speed but there's a lot of braking in between. Me? I just
put the tranny in neutral and roll down the entire five miles by giving up
potential energy, where I only brake when I must and I take the turns very
wide (as most people do) which helps maintain speed.

Somehow, _that_ process (which most people do, I think, but in gear most
likely), wears tires out like you can't believe, where tires get half the
stated mileage, as far as I can tell by aggregate conversations.

> Turn the wheels to a high level of lock and the obvious will confront
> you. The type of feathering will tell you what the actual cause is.

I do admit that I can't 'read' a tire very well. I've tried, but rotations
screw up the readings, and certainly there can be multiple causes.

The type of feathering I mostly see is the kind you can feel after only
about 1000 miles on the outside edge, for about 3 inches of tread, where
there is a sharp lip that is feathered into that outside tread that you can
only feel moving your hand clockwise over the front tire tread on the
outside 3 inches.

I need to learn more, but I think that's "normal" since it happens even
after I get a professional alignment. I'm due for one soon for a couple of
cars, which is why, instead of paying the $150 per vehicle, which for the 3
cars I want to do first, will be almost five hundred bucks, I'd rather buy
the tools to do it myself for that same five hundred bucks.
o Caster gauge (to measure caster & calculate camber)
o Caster jig (to lock onto the wheel for the caster gauge to be accurate)
o Wheel plates (to move the wheels for adjustment under suspension loading)
o Toe plates (to enable single-person linear measurement to centerline)

After having discussed this with Clare in the past, I know we can redneck
some of that, but overall, those four items seem to be the key items needed
for a home DIY check/change of caster, camber, & toe, do you agree?

[Clare Snyder]

I always try to run my front tires aver placard pressure by a few
pounds - ESPECIALLY on front wheel drive vehicles that will be
cornered hard (basically anything I drive except for the baby Fiat I'm
currently (babysitting) driving - which is a rear engine rear drive
swing axle car with bad rear shocks - - -

[Clare Snyder]

I'd be cranking in a couple degrees of negative camber for extensive
downhill twisties. And running about 36PSI minimum pressure in the
front tires.

You got that backwards - - - - You MEASURE camber and calculate
caster (unless you have PROPER equipment which measures both)

>o Caster jig (to lock onto the wheel for the caster gauge to be accurate)
>o Wheel plates (to move the wheels for adjustment under suspension loading)
>o Toe plates (to enable single-person linear measurement to centerline)
>
>After having discussed this with Clare in the past, I know we can redneck
>some of that, but overall, those four items seem to be the key items needed
>for a home DIY check/change of caster, camber, & toe, do you agree?

It might take a REAL PRO to modify the camber properly likely require
installation of either camber plates or long lower control arms (or
offset bushings)

[Xeno]

On 14/6/19 6:28 am, Arlen G. Holder wrote:
> On Thu, 13 Jun 2019 17:11:14 +1000, Xeno wrote:
>
>> You can check the camber all you like but the answer is more likely in
>> the SAI angles and you will be able to do SFA about that.
>
> Hi Xeno,
>
> Thanks for your purposefully helpful advice on kingpin inclination angle
> (aka steering axis inclination), and perhaps included angle, neither of
> which have I delved into yet (as I'm starting with camber, which is the
> basis for caster calculations, and where toe is relatively simple).
> <http://www.valleyofhastings.com/WheelAlignment2.pdf>

Use the term Steering Axis Inclination (SAI) as your vehicle likely does
not have kingpins. They are only found on trucks these days. I am of the
old school so I still use KPI but I found, when teaching apprentices,
the term is meaningless to them because most have never seen kingpins
much less worked on a vehicle so equipped.

>
> Other than Clare, you and maybe one or two other folks here are
> knowledgeable in the important details of home alignment checks &
> adjustments, where I don't usually disagree with anything you guys say, as
> you know more than I do.
>
> We have to remember a home DIY alignment check & adjust is sort of like
> doing a DIY tuneup versus a complete engine overhaul
> o A DIY caster/camber/toe check/adjust is to a professional alignment
> o as a DIY tuneup is to a professional engine blueprinting overhaul
>
> The fact is that the SIA is a "non adujstable" angle:
> <https://www.freeasestudyguides.com/included-angle.html>
>
> The fact it's not adjustable means it is in a different category than
> o caster
> o camber
> o toe

SAI, to the serviceman, is a *diagnosis angle* in much the same way as
*toe out on turns* (TOOT) is a diagnosis angle. If your toe is correct
but TOOT is incorrect, you can be assured that you have something that
is *bent*, usually a steering arm. Note, you cannot *adjust* TOOT in
cars as it is *designed in* as part of the Ackermann Angle.

Steep driving, urban driving, same thing really. You are at a greater
lock more often, even at slow speed, than when you are out on the
highways and freeways.

>
> Most seem to wear on the outside edge, which I still haven't figured out
> exactly why.

The term is Camber Scrub, and it caused a particular type of feathered
wear (for and aft feather IIRC) on the outside of the tyre, but it isn't
caused by the *camber angle* per se. It is caused by what SAI does to
the camber angles in a turn. Here is a video clip describing *one* of
the reasons for SAI.

https://www.youtube.com/watch?v=IZLiP_37Oso

The narrator focuses on the need to reduce unwanted feedback through the
steering. No mention is made of the other major reasons for SAI and that
is steering self centering and torque steer reduction. There are a
number of factors involved in steering stability and self centering
including; SAI, Caster, Camber, mechanical trail and tyre trail.

In this video clip he mentions the self centering effect at the end. He
states that turning the steering forces the axle (and wheel) down and,
in effect, lifts the front of the car. That provides the self centering
effect as the weight of the car will tend to return the steering to its
central or straight ahead position. That downward force also creates a
change in the *camber angle*.

https://www.youtube.com/watch?v=IUcZ63unEyU

But it is the camber angle the wheel adopts when at the turn position,
caused by SAI, that causes *camber scrub*.

This clip https://www.youtube.com/watch?v=VbReLNi2JP4 provides a very
good description of the steering functions. Skip to 13:50 for a
graphical display of the camber angle change when turning.

> The road is about 5 miles at about a 9 percent angle with very
> many 180 degree and even 270 degree switchbacks, but the speeds are rather
> slow, where the road is too narrow to even have panted centerlines and
> where the nominal speed limit for such roads is 25mph.

Definitely camber scrub territory.

>
> Given nobody drives 25 mph anywhere, we can figure it's something like 30
> mph to 40 mph top speed but there's a lot of braking in between. Me? I just
> put the tranny in neutral and roll down the entire five miles by giving up
> potential energy, where I only brake when I must and I take the turns very
> wide (as most people do) which helps maintain speed.
>
> Somehow, _that_ process (which most people do, I think, but in gear most
> likely), wears tires out like you can't believe, where tires get half the
> stated mileage, as far as I can tell by aggregate conversations.

Do the same distance on straight roads and you will have fairly even
tyre wear.

>
>> Turn the wheels to a high level of lock and the obvious will confront
>> you. The type of feathering will tell you what the actual cause is.
>
> I do admit that I can't 'read' a tire very well. I've tried, but rotations
> screw up the readings, and certainly there can be multiple causes.

It takes practice and, since I haven't operated a wheel aligner for a
very long time, I am *out of practice* but I've had the priciples
hammered into me over the decades ably assisted by having taught the
principles for some 20 years.

>
> The type of feathering I mostly see is the kind you can feel after only
> about 1000 miles on the outside edge, for about 3 inches of tread, where
> there is a sharp lip that is feathered into that outside tread that you can
> only feel moving your hand clockwise over the front tire tread on the
> outside 3 inches.

That sounds like camber scrub feathering - if I'm reading your
description correctly.

>
> I need to learn more, but I think that's "normal" since it happens even
> after I get a professional alignment. I'm due for one soon for a couple of

A *professional alignment* cannot fix a *symptom* that is considered
*normal* for the kind of driving you do. Any changes made to mitigate
camber scrub will cause a reduction in handling capability at speed.

> cars, which is why, instead of paying the $150 per vehicle, which for the 3
> cars I want to do first, will be almost five hundred bucks, I'd rather buy
> the tools to do it myself for that same five hundred bucks.
> o Caster gauge (to measure caster & calculate camber)
> o Caster jig (to lock onto the wheel for the caster gauge to be accurate)
> o Wheel plates (to move the wheels for adjustment under suspension loading)
> o Toe plates (to enable single-person linear measurement to centerline)
>
> After having discussed this with Clare in the past, I know we can redneck
> some of that, but overall, those four items seem to be the key items needed
> for a home DIY check/change of caster, camber, & toe, do you agree?
>

Yes, that is basically all the small service station had next door to
where I did my apprenticeship. You have missed the primary requisite
however - a guaranteed dead flat and level garage floor. Also a lock to
lock the steering wheel to the desired centre position;
https://i.ebayimg.com/images/g/sJIAAOSwImRYV58p/s-l225.jpg

[Arlen G. Holder]

On Thu, 13 Jun 2019 21:17:18 -0400, Clare Snyder wrote:

> I'd be cranking in a couple degrees of negative camber for extensive
> downhill twisties. And running about 36PSI minimum pressure in the
> front tires.

Hi Clare,
Good idea. I had her bring it over today where I cranked her up to 40psi on
all four tires. I'll keep an eye on it as I see her every day.

>>o Caster gauge (to measure caster & calculate camber)
>
> You got that backwards - - - - You MEASURE camber and calculate
> caster (unless you have PROPER equipment which measures both)

Yeah. That was a thinko. Thanks for catching it. We measure camber, which
is then used to calculate caster, which isn't adjustable in many cases
anyway.

One tool I might also need is a leveling tool so that all four wheels are
on a screw-mounted plate. Do you have a recommendation for that tool?

> It might take a REAL PRO to modify the camber properly likely require
> installation of either camber plates or long lower control arms (or
> offset bushings)

There is a difference between a tuneup and an engine overhaul, where the
caster, camber, and toe measurements will likely only result in the need
for changes if they're well off the spec, and if the OEM setup allows for
it.

For example, while you can measure anything, on the bimmer, the only thing
an OEM setup can change is rear camber & toe, and then front toe, in that
order - and that's it.

[Arlen G. Holder]

On Fri, 14 Jun 2019 12:58:31 +1000, Xeno wrote:

> Use the term Steering Axis Inclination (SAI) as your vehicle likely does
> not have kingpins.

Hi Xeno,
I typed up a super detailed response, after viewing every second of those
three videos, where the first and last seem to have the same graphics, and
the middle (whiteboard) one was a bit different - and where that wheelcam
shot of the tire literally bending away from the rim - and the temperature
methods of determining footprint on hard cornering were illuminating.

I hate losing data, but I lost it when the PC rebooted, so suffice to say I
appreciate the videos, from which I learned good stuff, particularly about
that "scrub radius".

I didn't find a lot on the net about "camber scrub", and those videos
didn't cover specific tire wear on the slow speed (less than 40mph)
constantly lock-to-lock turns we perform on the mountain, where the goal
is how to modify the set up for the vehicle in a compromise to minimize
that 'camber scrub' on FWD and RWD vehicles without adversely affecting
straight-line handling.

> Yes, that is basically all the small service station had next door to
> where I did my apprenticeship. You have missed the primary requisite
> however - a guaranteed dead flat and level garage floor. Also a lock to
> lock the steering wheel to the desired centre position;
> https://i.ebayimg.com/images/g/sJIAAOSwImRYV58p/s-l225.jpg

Everyone says you need a perfectly flat garage floor, which, as far as I
know, mine is pretty flat based on putting a level on it - but I don't
really know how flat is flat enough.

Given that a millimeter or two of height adjustment in any one corner might
be necessary for most garages, I guess your suggestion above adds two
nice-to-have tools to the home DIY alignment check mix...
o Steering wheel centering lock
o Some kind of way to put the 4 wheels on a wormscrew-adjusted plate

Googling found the first, but the second was in the thousand dollar range.

Are there good redneck solutions for leveling the four tires?

[Tekkie®]

Ed Pawlowski posted for all of us...

Remember Lorena Bobbitt? (How appropriate is the last name? 8~(

--
Tekkie

[Tekkie®]

Clare Snyder posted for all of us...

I had a set of early Hankooks and could not get rid of the vibration. IIRC I
got Conti's with very good results.

--
Tekkie

[Tekkie®]

Clare Snyder posted for all of us...


>

> Running the dang things half flat or cornering like an idiot - - -
>

Looked to me to be major under-inflation.

--
Tekkie

[Tekkie®]

Arlen G. Holder posted for all of us...

>
> I have two more tires to put on for her for her rears, which are worn more
> evenly (she probably doesn't rotate?) so I told her to wait until she
> needed them since they are just sitting outside (I moved them into the
> garage as they were getting dirty in the rain over the winter).
>

The better tires should-by tire manufacturers recommendation-be mounted on
the back.

--
Tekkie

[Clare Snyder]

What kind of heap is she driving????

[Clare Snyder]

A concrete grinder and a laser level

[Clare Snyder]

On Fri, 14 Jun 2019 14:51:53 -0400, Tekkie® <Tek...@comcast.net>
wrote:

Could never figure out exactly how many corners Hankook figured
there were in a circle - - - -

[Clare Snyder]

On Fri, 14 Jun 2019 15:05:56 -0400, Tekkie® <Tek...@comcast.net>
wrote:

That is only true for ONE risk - the risk of the rear tires breaking
away on a corner due to hydroplaning or poor traction.

In his case if he always put the best tires on the rear he would
continually be putting half worn tires on the axle that is eating
tires and requires the most traction (the downhill steering wheels and
the uphill "scrambling" wheels.

Doesn't make a LICK of sense in either case.

[Xeno]

The best tyres to the rear is for handling, keep the oversteer under
control. In that case, we're referring to the best *type* of tyre.
Radial versus crossply or steel belted radial versus textile radial.
Most run steel radials now so the basic premise is academic but the
basic rule is the best handling tyre when mixing tyre types.
When it comes to tread depth, yes, you are dealing then with the risk of
aquaplaning. More weight on the front means better water removal even on
lower tread depths. At the rear, on a FWD, there may be very minimal
mass on the rear tyres so pushing through water may be more difficult.
In summary, the best place for the newest tyres on a FWD is the rear.

[Clare Snyder]

On Sat, 15 Jun 2019 09:55:05 +1000, Xeno <xeno...@optusnet.com.au>
wrote:

>On 15/6/19 7:04 am, Clare Snyder wrote:
>> On Fri, 14 Jun 2019 15:05:56 -0400, Tekkie® <Tek...@comcast.net>
>> wrote:
>>
>>> Arlen G. Holder posted for all of us...
>>>
>>>
>>>>
>>>> I have two more tires to put on for her for her rears, which are worn more
>>>> evenly (she probably doesn't rotate?) so I told her to wait until she
>>>> needed them since they are just sitting outside (I moved them into the
>>>> garage as they were getting dirty in the rain over the winter).
>>>>
>>>
>>> The better tires should-by tire manufacturers recommendation-be mounted on
>>> the back.
>> That is only true for ONE risk - the risk of the rear tires breaking
>> away on a corner due to hydroplaning or poor traction.
>>
>> In his case if he always put the best tires on the rear he would
>> continually be putting half worn tires on the axle that is eating
>> tires and requires the most traction (the downhill steering wheels and
>> the uphill "scrambling" wheels.
>>
>> Doesn't make a LICK of sense in either case.
>>
>The best tyres to the rear is for handling, keep the oversteer under
>control. In that case, we're referring to the best *type* of tyre.
>Radial versus crossply or steel belted radial versus textile radial.
>Most run steel radials now so the basic premise is academic but the
>basic rule is the best handling tyre when mixing tyre types.

NOT.

You NEVER mix types from axle to axle - for MANY reasons - one of
which is legal.

>When it comes to tread depth, yes, you are dealing then with the risk of
>aquaplaning. More weight on the front means better water removal even on
>lower tread depths. At the rear, on a FWD, there may be very minimal
>mass on the rear tyres so pushing through water may be more difficult.
>In summary, the best place for the newest tyres on a FWD is the rear.

For cornering in wet weather or loose surfaces, yes. For powering
through corners or straight-line accelleration on clean dry pavement?
Mabee not.

Anywhere understeer is a possible problem , more than oversteer, you
want the best rubber on the front. On a FWD vehicle it is quite
difficult to induce oversteer to combat understeer - and FWD vehicles
tend towards understeer where you do NOT want bald front tires - - - .
On SEVERE trailing throttle you don't want bald tires on the rear
either.

Personally, I virtually ALWAYS replace tires in sets of 4 - and WELL
before the thread is gone !!! I don't put miles on fast enough any
more to wear good tires out before they "time out"

[Rod Speed]

"Xeno" <xeno...@optusnet.com.au> wrote in message
news:gmiqev...@mid.individual.net...

otoh you don’t see a fwd aquaplane much at all even with the tires
with the least tread on the rear wheels.

[Xeno]

On 15/6/19 2:55 am, Arlen G. Holder wrote:
> On Fri, 14 Jun 2019 12:58:31 +1000, Xeno wrote:
>
>> Use the term Steering Axis Inclination (SAI) as your vehicle likely does
>> not have kingpins.
>
> Hi Xeno,
> I typed up a super detailed response, after viewing every second of those
> three videos, where the first and last seem to have the same graphics, and
> the middle (whiteboard) one was a bit different - and where that wheelcam
> shot of the tire literally bending away from the rim - and the temperature
> methods of determining footprint on hard cornering were illuminating.

Yes, I learnt a couple of points from those videos too so it seems you
can teach old dogs new tricks. I have found, in order to gain a better
appreciation of steering geometry and suspension systems, one needs to
look at those places that are extreme. In this case, it's in motor racing.

>
> I hate losing data, but I lost it when the PC rebooted, so suffice to say I
> appreciate the videos, from which I learned good stuff, particularly about
> that "scrub radius".
>
> I didn't find a lot on the net about "camber scrub", and those videos

You won't. Information on it is scarce since it is an undesired effect.
However, if you look at what the wheel is doing vis a vis camber during
high angle (note - not high speed) cornering, then you can visualise the
issue. Note too that tread blocks have a limited degree of flexibility
and, as such, are likely to exceed that during high angle cornering
resulting in tread scrubbing.

> didn't cover specific tire wear on the slow speed (less than 40mph)
> constantly lock-to-lock turns we perform on the mountain, where the goal
> is how to modify the set up for the vehicle in a compromise to minimize
> that 'camber scrub' on FWD and RWD vehicles without adversely affecting
> straight-line handling.

The reality is that you are faced with a *compromise* and there are many
such in steering and suspension geometry. Any gain in the tyre wear
scenario will negatively affect high speed. If you happen to see a
Porsche Cayenne in a parking lot with its wheels turned at a high angle,
the camber angle displayed will amaze you. I know it amazed me. Of
course, when you realise that vehicle's suspension is *optimised* for
high speed and high power operation in a very narrow band either side of
straight ahead, it all makes sense.

>
>> Yes, that is basically all the small service station had next door to
>> where I did my apprenticeship. You have missed the primary requisite
>> however - a guaranteed dead flat and level garage floor. Also a lock to
>> lock the steering wheel to the desired centre position;
>> https://i.ebayimg.com/images/g/sJIAAOSwImRYV58p/s-l225.jpg
>
>
> Everyone says you need a perfectly flat garage floor, which, as far as I
> know, mine is pretty flat based on putting a level on it - but I don't
> really know how flat is flat enough.

A level will only give you a localised point. You need something that
can verify any point in the garage floor against a common datum point.
These can be used for that purpose and aren't expensive;
https://www.bosch-do-it.com/au/en/diy/tools/pll-360-set-3165140562898-199931.jsp
Or you could hire one for a day just to verify your garage floor. A
professional one of these should have been used when the floor was
poured and leveled anyway.

>
> Given that a millimeter or two of height adjustment in any one corner might
> be necessary for most garages, I guess your suggestion above adds two
> nice-to-have tools to the home DIY alignment check mix...
> o Steering wheel centering lock
> o Some kind of way to put the 4 wheels on a wormscrew-adjusted plate
>
> Googling found the first, but the second was in the thousand dollar range.
>
> Are there good redneck solutions for leveling the four tires?
>

Most wheel aligners that I have used come with ramps that have the added
benefit of raising the vehicle a couple of feet off the floor. Ramps,
even without the aligner heads, provide a relatively easy means of
leveling the required work area. They don't even need to be raised more
than an inch or two. If the floor area is really out of whack, two or
four ramps made of wood of varying thicknesses might suffice. You can
even check the level easily these days with laser levels as I mentioned
above. My brother has one of the professional units since he is a
concreter but cheaper DIY versions, like the one in the link, should
suffice for this purpose.

[Xeno]

Yes, I am well aware of that but it used to be legal, within limits, and
some unknowing individuals still do it.

>> When it comes to tread depth, yes, you are dealing then with the risk of
>> aquaplaning. More weight on the front means better water removal even on
>> lower tread depths. At the rear, on a FWD, there may be very minimal
>> mass on the rear tyres so pushing through water may be more difficult.
>> In summary, the best place for the newest tyres on a FWD is the rear.
>
> For cornering in wet weather or loose surfaces, yes. For powering
> through corners or straight-line accelleration on clean dry pavement?
> Mabee not.
>
> Anywhere understeer is a possible problem , more than oversteer, you
> want the best rubber on the front. On a FWD vehicle it is quite
> difficult to induce oversteer to combat understeer - and FWD vehicles
> tend towards understeer where you do NOT want bald front tires - - - .

I am not referring to *bald* tyres. I don't even let my tyres get to the
wear indicators as a rule. I like wet weather handling to be as optimal
as possible.

> On SEVERE trailing throttle you don't want bald tires on the rear
> either.

You do not want *bald* tyres anywhere on a vehicle. I am not referring
to bald tyres, just relative tread depth.

>
> Personally, I virtually ALWAYS replace tires in sets of 4 - and WELL
> before the thread is gone !!! I don't put miles on fast enough any
> more to wear good tires out before they "time out"
>

As I said before, ditto for me. I do clock up the mileage however. I am
25-30% above average mileage now in my 3 year old car.

[Xeno]

It is the manufacturers who are recommending newest to the rears. I
understand their logic since I also understand the handling dynamics of
a car.

[Rod Speed]

"Xeno" <xeno...@optusnet.com.au> wrote in message

news:gmjb9n...@mid.individual.net...

But given that I don’t see any aquaplaning with the rear wheels on my FWD,
I don’t buy their recommendation. Clare's comment covers that well.

> I understand their logic since I also understand the handling dynamics of
> a car.

Not with aquaplaning on the rear wheels of FWD cars you don’t.

[Peeler]

On Sat, 15 Jun 2019 16:16:41 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:

>> It is the manufacturers who are recommending newest to the rears.
>
> But given that I don’t see any aquaplaning with the rear wheels on my FWD,
> I don’t buy their recommendation.

Of COURSE not, auto-contradicting senile Rodent! LOL

--
Kerr-Mudd,John addressing senile Rot:
"Auto-contradictor Rod is back! (in the KF)"
MID: <XnsA97071CF43...@85.214.115.223>

[Peeler]

On Sat, 15 Jun 2019 11:39:38 +1000, cantankerous trolling geezer Rodent

Speed, the auto-contradicting senile sociopath, blabbered, again:

>> lower tread depths. At the rear, on a FWD, there may be very minimal mass
>> on the rear tyres so pushing through water may be more difficult.
>> In summary, the best place for the newest tyres on a FWD is the rear.
>
> otoh you don’t see a fwd aquaplane much at all even with the tires
> with the least tread on the rear wheels.

In auto-contradicting mode again, senile asshole? LOL

[Xeno]

Did I not say that it isn't just for *aquaplaning*? The idea is to
reduce slip angles at the rear to control oversteer tendencies. This is
all the time, not just when aquaplaning. All cars are designed with
inbuilt understeer - even rear wheel drive cars. If you want to argue
the toss, then take it up with the tyre manufacturers. After all, it's
their recommendation for their own product so I feel safe in assuming
they would have a better idea than Joe Blow off the street.

[Clare Snyder]

On Sat, 15 Jun 2019 14:24:27 +1000, Xeno <xeno...@optusnet.com.au>
wrote:

>On 15/6/19 10:30 am, Clare Snyder wrote:

>>
>> You NEVER mix types from axle to axle - for MANY reasons - one of
>> which is legal.
>
>Yes, I am well aware of that but it used to be legal, within limits, and
>some unknowing individuals still do it.

OI t was illegal already back in 1969
>

[Rod Speed]

"Xeno" <xeno...@optusnet.com.au> wrote in message

news:gmkg1k...@mid.individual.net...

The other effects are even less likely.

> The idea is to reduce slip angles at the rear to control oversteer
> tendencies.

Oversteer just isnt a problem with fwd cars.

> This is all the time, not just when aquaplaning. All cars are designed
> with inbuilt understeer - even rear wheel drive cars.

fwd cars understeer regardless of the design.

> If you want to argue the toss, then take it up with the tyre
> manufacturers.

My tire manufacture isnt stupid enough to say that.

> After all, it's their recommendation for their own product

It isnt with mine.

> so I feel safe in assuming they would have a better idea than Joe Blow off
> the street.

Its basic physics and trivial to prove that the
car doesn’t do any better with the new tires
on the back with a fwd car.

[Peeler]

On Sun, 16 Jun 2019 05:47:57 +1000, cantankerous trolling geezer Rodent

Speed, the auto-contradicting senile sociopath, blabbered, again:

> Its basic physics and trivial to prove that the
> car doesn’t do any better with the new tires
> on the back with a fwd car.

What could be more trivial than your senile trolling on all these groups,
you abnormal senile pest?

--
FredXX to Rot Speed:
"You are still an idiot and an embarrassment to your country. No wonder
we shipped the likes of you out of the British Isles. Perhaps stupidity
and criminality is inherited after all?"
Message-ID: <plbf76$gfl$1...@dont-email.me>

[Xeno]

It wasn't illegal in this country back in 1969. There were specific
limits to what you could do but the only legal requirement, as I recall,
was the tyres had to be the same on the same *axle*.

I found, even though you could in that era have different tread patterns
front to rear, you needed to ensure the best *handling* tyre was at the
rear. This was not always easy to determine as I found out when I
couldn't buy tyres to match the tread pattern on a car I owned and
bought two tyres which looked very similar tread wise to the existing
pair. Both types were textile radials and I fitted the new ones to the
front. The rear tyre tread depth was very close to that of the new front
tyres. What I found however was that the new tyres were way too precise
with very low slip angles. When in even moderate cornering situations,
the front would spear into a corner with minimal understeer
characteristics whilst the rear displayed tail happy behaviour. The car
felt *pigeon toed* as if the front wheels had extreme toe in settings. I
couldn't leave it like that because my wife was the primary driver of
that car so I reversed the set and it made the car stable once more. Not
long afterwards I bought another 2 tyres and matched the existing new
ones to give much more balanced handling and used the originals on a
trailer. Whilst it appeared only to be a tread pattern difference, it
soon became obvious that handling characteristics were vastly different
between the two types and probably involved much more than the tread
pattern alone. It wasn't possible to deduce this from merely looking at
the tyres, it required a run on the road to discern the characteristics.

When I first entered the automotive industry, crossply tyres were king
and radials were just entering general use. It was the recommendation at
that time, if mixing types, to place crossplies at the front, the
radials at the rear. As steel belted radials entered the scene, it was
recommended that, if mixing the two radial types, that the steel belted
radials were fitted to the rear and textile radials to the front. The
reasoning back then was simple - cross ply tyres had the greatest slip
angle characteristics, textile radials had lower slip angle
characteristics and steel belted radials had the lowest slip angle
characteristics of all. It was always mandatory to have tyres matched on
the same axle according to roadworthy laws but the front to rear
placement was Ok if you followed the above guidelines. As I found
however, it wasn't always that simple and there were situations which
were a case of try it and see. Since that time I have always bought
tyres as a set of four at a minimum, fitted them all at the same time
and followed tyre rotation procedures.

As for the legality of different tyres front to rear, some new vehicles
would fall afoul of that since they have a larger rim size at the rear,
usually in width but occasionally in diameter. Some small vans have a
larger diameter wheel at the front, a smaller on at the rear for a
flatter cargo space but, in these cases, the rear are *duals*.

[Arlen G. Holder]

On Sat, 15 Jun 2019 14:14:27 +1000, Xeno wrote:

> You won't. Information on it is scarce since it is an undesired effect.
> However, if you look at what the wheel is doing vis a vis camber during
> high angle (note - not high speed) cornering, then you can visualise the
> issue. Note too that tread blocks have a limited degree of flexibility
> and, as such, are likely to exceed that during high angle cornering
> resulting in tread scrubbing.

Hi Xeno,

While I don't race, our conditions are "extreme" enough, in that constant
incessant repeated nearly full back-to-back wheel locks are causing
"something" to scrape away rubber, so this "camber scrub" is intriguing.

I snapped this photo of tires that I mounted about a month ago, which only
have about 1000 miles on them, where they clearly show this pattern which
"might" be what you've been referring to as "camber scrub".
<https://i.postimg.cc/zvvyL2tq/mount24.jpg>

Does _that_ feathering look like what you're referring to as "camber scrub"?

[Xeno]

On 16/6/19 4:31 pm, Arlen G. Holder wrote:
> On Sat, 15 Jun 2019 14:14:27 +1000, Xeno wrote:
>
>> You won't. Information on it is scarce since it is an undesired effect.
>> However, if you look at what the wheel is doing vis a vis camber during
>> high angle (note - not high speed) cornering, then you can visualise the
>> issue. Note too that tread blocks have a limited degree of flexibility
>> and, as such, are likely to exceed that during high angle cornering
>> resulting in tread scrubbing.
>
> Hi Xeno,
>
> While I don't race, our conditions are "extreme" enough, in that constant
> incessant repeated nearly full back-to-back wheel locks are causing
> "something" to scrape away rubber, so this "camber scrub" is intriguing.

That is also considered *extreme* even though you aren't doing it fast.

>
> I snapped this photo of tires that I mounted about a month ago, which only
> have about 1000 miles on them, where they clearly show this pattern which
> "might" be what you've been referring to as "camber scrub".
> <https://i.postimg.cc/zvvyL2tq/mount24.jpg>
>
> Does _that_ feathering look like what you're referring to as "camber scrub"?
>

It does indeed! Same kind of feathering I'm getting on my Toyota's front
tyres - a feathering that you can easily feel in the early stages as you
run your hands for and aft along that section of tread area. Now try to
imagine what those tread blocks are doing as they roll around in a tight
circle with heaps of camber gain. It's not pretty and, worse, there is
SFA you can do about it.

BTW, positive caster will accentuate the camber scrub. Caster is
generally not a tyre wearing angle. However, the more caster your
steering has, the more camber *change* you will get when turning the
steering. Positive caster will give you a beneficial gain in terms of
handling. You will get more camber gain (more +ve) on the inside wheel
but the outside wheel will experience camber *loss* and become more
vertical or even negative. Since the more vertical tyre is on the
outside, the tread will get more grip with reduced slip angle aided by
weight transfer. This is great for cornering at speed. However when
travelling at slow speeds, weight transfer is not as significant and the
camber angle on the inside wheel, the one at the tightest lock, heads
towards positive extremes. It is, in effect, riding heavily on the outer
edge of the tread and this is where, and why, the damage is being done.
The tread blocks have only so much flex before they are forced to break
contact with the road and slide. You've seen the evidence of what that does.

Caster specifications are usually given as a range, say between 1 and 2
degrees with a side to side variation limit. All you can really do to
mitigate the effect is to set your caster to the low end of the
specified range.

[Arlen G. Holder]

On Sun, 16 Jun 2019 20:40:34 +1000, Xeno wrote:

> It does indeed! Same kind of feathering I'm getting on my Toyota's front
> tyres - a feathering that you can easily feel in the early stages as you
> run your hands for and aft along that section of tread area.

Thanks for that information, where the one correction I need to make is
that you can only feel this feathering running your hand "*backward*"
(clockwise) over the outside quarter of the tread pattern.
<https://i.postimg.cc/zvvyL2tq/mount24.jpg>

If you run your hand toward the front (counterclockwise), you can't feel
the feathering because each "lip" is downward.
<https://i.postimg.cc/vTZLmZrN/mount25.jpg>

When you run your hand toward the rear of the vehicle, each lip is upward.
<https://i.postimg.cc/X7hcV3ps/mount26.jpg>

That's the oddity. The feathering is only one way.
<https://i.postimg.cc/KYhPMN7L/mount27.jpg>

It's reproducible for years - so it's always the same.
That one-way lip feathering should be diagnostic, should it not?
<https://i.postimg.cc/Wzyrb6bd/mount28.jpg>

> BTW, positive caster will accentuate the camber scrub. Caster is
> generally not a tyre wearing angle. However, the more caster your
> steering has, the more camber *change* you will get when turning the
> steering.

Hmmmmmmmm.... maybe I can consider lessening positive caster a teeny bit?

> Positive caster will give you a beneficial gain in terms of
> handling. You will get more camber gain (more +ve) on the inside wheel
> but the outside wheel will experience camber *loss* and become more
> vertical or even negative. Since the more vertical tyre is on the
> outside, the tread will get more grip with reduced slip angle aided by
> weight transfer. This is great for cornering at speed. However when
> travelling at slow speeds, weight transfer is not as significant and the
> camber angle on the inside wheel, the one at the tightest lock, heads
> towards positive extremes.

This is very useful information, as all our lock-to-lock cornering is at
30mph to 40mph ... never faster because I ran a test last week where
anything over 40mph is impossible to do even remotely safely, as all the
turns are blind turns and the file miles of 9% twisty road can't even be
twenty feet wide at the maximum (I should measure it but it's something
like that, as it's too narrow for the county to center stripe it legally).

> It is, in effect, riding heavily on the outer
> edge of the tread and this is where, and why, the damage is being done.

I need to study more - where your conclusion is spot on perfect but where I
don't get the individual steps only because I think of alignment as being
'static' so to speak. I know it changes - but my brain doesn't know 'how'
it changes under those slow speed lock-to-lock downhill (or uphill) turns.

> The tread blocks have only so much flex before they are forced to break
> contact with the road and slide. You've seen the evidence of what that does.

Yes. That's for sure. The outer tread blocks "feather" such that you can
feel it, and barely see it, after about 1000 miles. The only thing I can
do, is change the alignment or rotate every 1000 miles (but even rotation
won't stop it - it just evens it out with the rears).

> Caster specifications are usually given as a range, say between 1 and 2
> degrees with a side to side variation limit. All you can really do to
> mitigate the effect is to set your caster to the low end of the
> specified range.

That's EXACTLY what I'll do!
I have to admit I need to read, and re-read and re-read again what you
wrote above, as my brain needs to work in step-by-step fashion.

You didn't skip a step but I don't quite "believe" in my brain all the
steps, if you know what I mean. It's not that I don't believe you, but that
my brain has to understand EACH step before moving to the next step when it
comes to UNDERSTANDING why this happens. (It's kind of like a series of
math equations where I need to understand every step.)

On the other hand, once there is a conclusion, I can EXPERIMENT easily,
which is how a lot of cars get fixed (by throwing parts at the problems
without understanding them). So I will change the caster.

I have an alignment shop which runs a sale for $30 off to drop the $160
price to $130 who lessened my bimmer's rear camber from negative 2 degrees
to almost 0 degrees - where if I go to him - I can ask for the least caster
in the spec.

Better yet, I need to buy the tools to do that caster change myself - but
that's a topic for a different thread since I have to MEASURE it first.

[Clare Snyder]

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

[Arlen G. Holder]

On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

> Just applying negative camber MAY be simpler and will accomplish the
> same thing, without affecting lateral stability..
>
> However, with the shoulder wear on BOTH edges, the most effective
> change you can make is to "air up" the tires. Keep the carcass of the
> tire rigid - prevent the tire from "rolling" out on the outer corner
> and "rolling in" on the inner corner will cause the tread to wear more
> evenly across the face of the tire - and tereby REDUCE the total wear.
> I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H->X->H->X->H->X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
<https://i.postimg.cc/63Kc80x9/mount29.jpg>

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X->H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.

[Xeno]

On 17/6/19 6:41 am, Arlen G. Holder wrote:
> On Sun, 16 Jun 2019 20:40:34 +1000, Xeno wrote:
>
>> It does indeed! Same kind of feathering I'm getting on my Toyota's front
>> tyres - a feathering that you can easily feel in the early stages as you
>> run your hands for and aft along that section of tread area.
>
> Thanks for that information, where the one correction I need to make is
> that you can only feel this feathering running your hand "*backward*"
> (clockwise) over the outside quarter of the tread pattern.
> <https://i.postimg.cc/zvvyL2tq/mount24.jpg>
>
> If you run your hand toward the front (counterclockwise), you can't feel
> the feathering because each "lip" is downward.
> <https://i.postimg.cc/vTZLmZrN/mount25.jpg>
>
> When you run your hand toward the rear of the vehicle, each lip is upward.
> <https://i.postimg.cc/X7hcV3ps/mount26.jpg>
>
> That's the oddity. The feathering is only one way.
> <https://i.postimg.cc/KYhPMN7L/mount27.jpg>

Not really. You are only driving in the one direction so the feathering
will only be in one direction. If it were in both directions, it
wouldn't be feathering, it would be *scalloping*, a diagnosis for a
different cause.

>
> It's reproducible for years - so it's always the same.
> That one-way lip feathering should be diagnostic, should it not?
> <https://i.postimg.cc/Wzyrb6bd/mount28.jpg>
>
>> BTW, positive caster will accentuate the camber scrub. Caster is
>> generally not a tyre wearing angle. However, the more caster your
>> steering has, the more camber *change* you will get when turning the
>> steering.
>
> Hmmmmmmmm.... maybe I can consider lessening positive caster a teeny bit?

You could experiment with it. After all, caster is not the only driver
of steering returnability but you need to be very judicious in doing so
noting that steering will be less precise, possibly more vague.
Regardless, any caster reduction will be only part of the story since
the primary cause, SAI, is well out of your control as it is a designed
in feature.

>
>> Positive caster will give you a beneficial gain in terms of
>> handling. You will get more camber gain (more +ve) on the inside wheel
>> but the outside wheel will experience camber *loss* and become more
>> vertical or even negative. Since the more vertical tyre is on the
>> outside, the tread will get more grip with reduced slip angle aided by
>> weight transfer. This is great for cornering at speed. However when
>> travelling at slow speeds, weight transfer is not as significant and the
>> camber angle on the inside wheel, the one at the tightest lock, heads
>> towards positive extremes.
>
> This is very useful information, as all our lock-to-lock cornering is at
> 30mph to 40mph ... never faster because I ran a test last week where
> anything over 40mph is impossible to do even remotely safely, as all the
> turns are blind turns and the file miles of 9% twisty road can't even be
> twenty feet wide at the maximum (I should measure it but it's something
> like that, as it's too narrow for the county to center stripe it legally).

I was going to suggest you run wide arcs around the bends but it seems
that's not even possible.

>
>> It is, in effect, riding heavily on the outer
>> edge of the tread and this is where, and why, the damage is being done.
>
> I need to study more - where your conclusion is spot on perfect but where I
> don't get the individual steps only because I think of alignment as being
> 'static' so to speak. I know it changes - but my brain doesn't know 'how'
> it changes under those slow speed lock-to-lock downhill (or uphill) turns.

It's what the tread is doing at the contact patch that is the critical
issue here and that is damn difficult to visualise. Start with the
forces acting on a tyre contact patch and you will see what I mean;

http://racingcardynamics.com/racing-tires-lateral-force/

In particular, this diagram;

http://racingcardynamics.com/wp-content/uploads/2014/10/Figure3.jpg

In your case, that contact patch centre of pressure will be off to the
outside and not even. See the curved path? No small wonder that tread
block deformation occurs.

Once I started to understand the forces creating slip angles, then I
began to get the bigger picture on tyre wear and, more importantly,
handling.
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQKH0LYwk36kSkAbeliaY0KXsTCwozgQQBfvgC77M7U1oj7bpK3ow

Again note the curved path through the contact patch while cornering.
That is the start point to understanding the concept as that is a result
of the combination of forces acting at that pint..

>
>> The tread blocks have only so much flex before they are forced to break
>> contact with the road and slide. You've seen the evidence of what that does.
>
> Yes. That's for sure. The outer tread blocks "feather" such that you can
> feel it, and barely see it, after about 1000 miles. The only thing I can
> do, is change the alignment or rotate every 1000 miles (but even rotation
> won't stop it - it just evens it out with the rears).

I am presented with that same fait acompli with my car. My case is not
as bad as yours as I get ~60,000 kilometres per set of tyres anyway,
even with camber scrub issues.

>
>> Caster specifications are usually given as a range, say between 1 and 2
>> degrees with a side to side variation limit. All you can really do to
>> mitigate the effect is to set your caster to the low end of the
>> specified range.
>
> That's EXACTLY what I'll do!
> I have to admit I need to read, and re-read and re-read again what you
> wrote above, as my brain needs to work in step-by-step fashion.

You aren't Robinson Crusoe in that respect. It has taken me years to
come to the level of understanding of steering I now have. I have a
greater understanding of steering and handling now than had when I was
teaching the topic at a technical college. I have found traditional
texts on the topic aren't sufficient to give one the depth of
understanding required - seek instead engineering texts on the topic and
those devoted to motor racing. Those who work at the extremes of
handling seem to have a better idea of what's happening at that contact
patch.

>
> You didn't skip a step but I don't quite "believe" in my brain all the

I probably did. There is a whole section there on what actually happens
when that tread passes through the contact patch. I cannot find a
suitable diagram that provides, in and of itself, a decent explanation
save for those on slip angle forces linked above because, as you have
noted, it is difficult to picture in your mind what is going on.

> steps, if you know what I mean. It's not that I don't believe you, but that
> my brain has to understand EACH step before moving to the next step when it
> comes to UNDERSTANDING why this happens. (It's kind of like a series of
> math equations where I need to understand every step.)

I know what you mean. It has taken me a long time and a lot of reading
about steering geometry before I had enough of an understanding how it
all works.

>
> On the other hand, once there is a conclusion, I can EXPERIMENT easily,
> which is how a lot of cars get fixed (by throwing parts at the problems
> without understanding them). So I will change the caster.

A lot of cars have *money* wasted on them following that process. Far
better to understand system operation and then experiment around the
causes of the problem in order to effect a better *compromise* that
mitigates your issue. As has been noted, you will not likely be able to
cure your issue since it is a result of steering geometry compromise
favouring highway operation but you now have a more precise start point.

>
> I have an alignment shop which runs a sale for $30 off to drop the $160
> price to $130 who lessened my bimmer's rear camber from negative 2 degrees
> to almost 0 degrees - where if I go to him - I can ask for the least caster
> in the spec.

You might want to discuss with him your issue and why you want to change
the spec. Get him onside.

>
> Better yet, I need to buy the tools to do that caster change myself - but
> that's a topic for a different thread since I have to MEASURE it first.
>

[Xeno]

On 17/6/19 8:48 am, Arlen G. Holder wrote:
> On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:
>
>> Just applying negative camber MAY be simpler and will accomplish the
>> same thing, without affecting lateral stability..
>>
>> However, with the shoulder wear on BOTH edges, the most effective
>> change you can make is to "air up" the tires. Keep the carcass of the
>> tire rigid - prevent the tire from "rolling" out on the outer corner
>> and "rolling in" on the inner corner will cause the tread to wear more
>> evenly across the face of the tire - and tereby REDUCE the total wear.
>> I'd bet about 3/4 of the wear is caused on the downhill.
>
> Hi Clare,
> I appreciate your advice as you and Xeno know this stuff whereas the rest
> just make it all up it seems.
>
> If adding more negative camber is even better than reducing the positive
> caster, then that's easier, as you noted, and likely better on high speed
> straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.

>
> I will take your advice on the multi-side shoulder wear, by bringing the
> front tires of this RWD vehicle to 40psi or so, which I understand and
> where I appreciate that advice.
>
> Since these tires were religiously rotated every 5K miles using a pattern I
> devised myself of H->X->H->X->H->X, etc., the tires ended up wearing
> "relatively" evenly overall, which is shown in this shot of the rears:
> <https://i.postimg.cc/63Kc80x9/mount29.jpg>
>
> I was just about to mount & balance these rear tires as we type where you
> can see they're worn sort of kind of evenly except in the inside edge,
> where these were mostly worn when on the front axle.

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?
Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that. As I have stated
previously, the camber of the tyre on the outside of the turn loses
camber and goes more vertical whilst the tyre on the inside of the turn
goes from slightly positive to heavily positive. The tyre on the outside
of the turn could be heading slightly into negative territory but that
would depend on static camber settings and would be minimal. Certainly
the tyre at the high positive camber will be doing most of the shoulder
wearing in those sharp slow speed turns.

>
> I likely should flip them on the wheel at the 10,000 mile mark after the
> first two X->H rotations have been done, which will move the inside edge to
> the outside edge. These darn tires have a whitewall stripe, which I hate,
> so that's why I didn't flip them on the rims prior.
>

[Arlen G. Holder]

On Mon, 17 Jun 2019 15:01:47 +1000, Xeno wrote:

> Just refresh my memory here, was it the *inside* or the *outside* of
> your tread that was wearing more and with the longitudinal feathering?

Hi Xeno,
I'm sorry for causing confusion.

The feathering is on the OUTSIDE edge of both front tires.
<https://i.postimg.cc/zvvyL2tq/mount24.jpg>

If I said otherwise, it was my mistake.

> Camber scrub tends to affect the *outside* edge of the tyre. For it to
> affect the *inside edge*, the camber on the tyre would need to be going
> well into the negative. It really can't be doing that.

You can feel it on the edge of the tire closest to you when you stand next
to the tire, which is the OUTSIDE edge.

I apologize if I said otherwise.

I need to learn more about camber scrub in slow speed turns!

[Xeno]

On 17/6/19 3:32 pm, Arlen G. Holder wrote:
> On Mon, 17 Jun 2019 15:01:47 +1000, Xeno wrote:
>
>> Just refresh my memory here, was it the *inside* or the *outside* of
>> your tread that was wearing more and with the longitudinal feathering?
>
> Hi Xeno,
> I'm sorry for causing confusion.
>
> The feathering is on the OUTSIDE edge of both front tires.
> <https://i.postimg.cc/zvvyL2tq/mount24.jpg>
>
> If I said otherwise, it was my mistake.

Well, I was misled by your words and Clare's on the topic of wear on
*both sides*.

>
>> Camber scrub tends to affect the *outside* edge of the tyre. For it to
>> affect the *inside edge*, the camber on the tyre would need to be going
>> well into the negative. It really can't be doing that.
>
> You can feel it on the edge of the tire closest to you when you stand next
> to the tire, which is the OUTSIDE edge.
>
> I apologize if I said otherwise.

No probs.

>
> I need to learn more about camber scrub in slow speed turns!
>

Might I suggest that the first thing you look at is the contact patch
and, with it, slip angles. That will give you a great deal of insight
into what is happening down at that critical part of your tyre.

Once you study slip angles, some of the mysteries of suspension and
steering geometry will begin to unfold.

Here is an example.
No doubt you have heard of the Ackermann Angle. It is the one that
allows your inner and outer wheels to follow a different path on turns,
the inner being at a tighter radius. This explains it, sort of;

https://www.youtube.com/watch?v=oYMMdjbmQXc

The way he describes it, the line through both rear wheels is the
critical one.

This pic shows the same diagram plus the one showing how they achieve
the Ackermann Angle.

https://www.pinterest.com.au/pin/185843922100707086/

The steering arms are inclined inwards so that the intersect point, the
turning centre, is at the centre of the rear axle. The problem is - no
car is built this way. When I was an apprentice, we were taught this
principle. Some diagrams were shown as above, some were shown with the
intersect point somewhat further forward of the rear axle and along the
centreline. No explanation was given back then for this difference. The
intersect point at the rear axle centreline works *if* you neglect slip
angle - as Ackermann quite obviously did. Given that the patent was
filed in 1818 and was intended for horse drawn vehicles, it likely
worked well enough in that situation, especially given wheels typically
had iron rims.

When slip occurs at the tyre contact patches, the *turning centre* will
move forward. The extent of this move forward will be dependent on the
relationship between the slip angles front and rear. High cornering
forces create roll and demand greater slip angles from the outer tyres
than the inner. Ackermann's principle then was based on a false premise.
Vehicles use what is known as a *modified Ackermann*.

To better understand this you need to delve into slip angles and then
progress to the dynamic handling of a vehicle when cornering. It gets
very complicated when you start looking at the geometry of the various
suspension systems. Some rear suspensions, for instance, create *toe in*
at the outer rear wheel under body roll. This has an effect on slip
angles and counters oversteer.

[Clare Snyder]

On Mon, 17 Jun 2019 15:01:47 +1000, Xeno <xeno...@optusnet.com.au>
wrote:

Adding negative camber will countderact the effects of SAI. Increased
SAI (or "included angle" in the spindle) causes more change in camber
as the wheel leaves the center position.. Changing camber DOES NOT
AFFECT SAI. When turning in a downhill thrusting turn the outer tire
will have a negative shift in camber while the inner wheel will have a
positive shift. The more positive caster, the more pronounced this
"tilt" or "corner carving" tendancy. If the tires are not stiff
enough or are underinflated, the tires will wear excessively on the
side facing the outside of the turn. If the tires ARE stiff enough or
inflated hard, the wear will tend to move towards the side of the tire
on the INSIDE of the turn - tending to even the wear across the face
of the tire.

That's why my FIRST recommendation is to air up the tires, and to
reduce the wear on the outside of the turn, possibly increase the
negative camber. Setting the caster to the high side of the positive
spec will give you extra negative camber on turns without any possible
negative effects of negative camber on the straight and level. It's
all a compromize. Dive and roll come into play along with road
banking.

a good article on camber change is here:
https://www.hotrod.com/articles/camber-change-static-dynamic-tire-traction/.
It is slanted towards circle track racing, but covers all the basics.

[Arlen G. Holder]

On Tue, 18 Jun 2019 00:44:17 +1000, Xeno wrote:

> Might I suggest that the first thing you look at is the contact patch
> and, with it, slip angles. That will give you a great deal of insight
> into what is happening down at that critical part of your tyre.

Hi Xeno,
THANK YOU for that suggestion to concentration on understanding the
dynamics of the contact patch first in hard downhill cornering.

I have to admit that I've read (and re-read) what you've written, but it's
like a series of math equations, where I can only grasp the starting point
and the ending point - but I can't make the connection to each of the
interim equations.

What makes things infinitely worse is that, as you're aware, I only care
about the slow-speed 20 to 35mph mostly) downhill (mostly) lock-to-lock
cornering forces that are causing the unidirectional feathering on the
outside corner.

There's precious little on the net about that specific problem, where,
everything I read seems to be about high speed racing with much greater
radii corners, which just isn't what's going on here.

I said before our corners are 180 degrees and 270 degrees where I realized
belatedly that none are 270 degrees, but many are 90 degrees (and, in fact,
most are 90 degrees) where about 1/10th are 180 degree hairpins.

Interestingly, I noticed that the hairpins all have a "pullout area" (for
trucks, I guess, which always back up forward and backward for a few tries
before they can make the turn).

So we "can" take a hairpin wide but only if the direction we're going has
the pullout, as the pullouts are always in the uphill side of the road,
which can be on either side of the road depending on the switchback.

> Once you study slip angles, some of the mysteries of suspension and
> steering geometry will begin to unfold.

Again, thank you for suggesting a way for my brain to begin to grasp the
singular problem.

Do you agree with my assessment that downhill is worse than uphill?

And, is the outside tire (the tire furthest from the center of the curve)
the tire that wears most from this feather scrubbing?

[Tekkie®]

Clare Snyder posted for all of us...


>
> On Fri, 14 Jun 2019 14:51:53 -0400, Tekkie® <Tek...@comcast.net>
> wrote:
>
> >Clare Snyder posted for all of us...
> >
> >
> >>
> >> On Wed, 12 Jun 2019 05:52:33 -0000 (UTC), "Arlen G. Holder"
> >> <arling...@nospam.net> wrote:
> >>
> >> >Clare - are smaller car tires easier to balance than SUV tires?
> >> ><https://i.postimg.cc/kG1M7cLd/mount15.jpg>
> >> >
> >> >A neighbor was in need of tires who knew that I had bought a few extra for
> >> >her long ago where they've been sitting outside in the rain & mud for
> >> >months waiting for her to need them.
> >> ><https://i.postimg.cc/7L8HPbtb/mount16.jpg>
> >> >
> >> >She finally wore through the belts and had to stop over for an "emergency"
> >> >tire change, which I did for her, but she was in a rush so we did it in
> >> >about 20 minutes from start to finish.
> >> >
> >> >I had to do it so fast that I didn't see the yellow dot until I looked at
> >> >this picture, where I mounted the red dot to the valve stem instead of the
> >> >yellow dot as you had recommended for when there are no match mounting
> >> >marks.
> >> >
> >> >I did statically balance and she reported no vibration whatsoever. I didn't
> >> >spend a lot of time cleaning up things so I'm surprised there's no
> >> >imbalance given how quickly I did the job for her.
> >> >
> >> >Just wondering if you've found that these tiny 14-inch tires are a piece of
> >> >cake compared to the normal truck SUV tires (like the Optimo's that I'm
> >> >used to) both in terms of mounting and balancing?
> >>
> >>
> >> Yes and no. The smaller tire has less total mass so a small amount
> >> of weight has more effect than it would on a bigger tire - but it is
> >> not as far from the center (shorter moment arm) so it has less effect.
> >>
> >> GOOD tires of any size are easier to ballance than crappy tires. Ealy
> >> Hankooks were a real pain to ballance. Apparentlythey have gotten
> >> better.
> >
> >I had a set of early Hankooks and could not get rid of the vibration. IIRC I
> >got Conti's with very good results.
> Could never figure out exactly how many corners Hankook figured
> there were in a circle - - - -

Good one!

--
Tekkie

[Tekkie®]

Clare Snyder posted for all of us...


>

> However, with the shoulder wear on BOTH edges, the most effective
> change you can make is to "air up" the tires. Keep the carcass of the
> tire rigid - prevent the tire from "rolling" out on the outer corner
> and "rolling in" on the inner corner will cause the tread to wear more
> evenly across the face of the tire - and tereby REDUCE the total wear.
> I'd bet about 3/4 of the wear is caused on the downhill.
>

+1 Keep the contact area against the pavement.

--
Tekkie

[Xeno]

That assumes the tyre starts out vertical with respect to the road. In
the case of camber scrub, the tyre on the inside of the turn is going to
extreme positive camber angles whereas the tyre on the outside *loses*
camber and becomes more vertical. that means the outside tyre sits more
flat on the road. The inside tyre, on the other hand, has gained camber
and is riding hard on its outer tread edge. The above scenario, with the
tyres *aired up*, keeps the tyre rigid and applies *more pressure
(force)* to the outside edge that is already in heavy contact with the
road. The centre of the tread is where most of the deflection occurs as
you increase the pressure - most with crossply tyres, least with steel
belted radials. Why do you think it is that radial tyres have minimal
static camber angles? It is because they naturally sit flatter on the
road with sidewall deformation rather than tread area deformation.
Another aspect is that weight transfer is negligible in slow speed
cornering and even if it were, that would still mean that the inside
tyre still gets scuffing because the load gets reduced and tread slip
occurs earlier than if the tread blocks were forced to maintain contact
longer. The inside tyre is the one at the extreme camber angle. If it's
a radial or, more so, a steel belted radial, it is designed to operate
with minimal camber.

[Xeno]

Are you sure about that? SAI is, after all, Steering Axis Inclination.

If we are talking about a *King Pin* in a beam axle arrangement, the KPI
angle is absolutely fixed and cannot be altered without recourse to
*bending* something.

In terms of modern cars, however, king pins are obsolete. The last
vehicle I can recall working on that had king pins was mid 60s.

What we use now are, as you know, ball joints to anchor the steering
knuckle yet allow multi-degree articulation. Makes the kinematics a damn
sight easier to work out from the engineer's design viewpoint.

https://www.freeasestudyguides.com/graphics/sai-sreering-axes-inclination..png

In the diagram above, there is a line referencing *true vertical*,
another referencing the SAI *angle*, and another referencing the tyre
camber angle. The *included angle* cannot be altered. It is designed in
and the only way to change that would be to *bend something*. In this
case, that something would be the steering knuckle. Definitely not
recommended but something that used to be done in vehicles of the 50s
and 60s when you ran out of adjustment. I was fortunate I never needed
to do that.

Looking at the linked diagram, if I feel the camber angle is too great,
what options do I have. I have to move one of the ball joints in
relation to the other. Assume the adjustment for camber is shims at the
inner end of the top control arm. So I set to and remove sufficient
shims to move upper control arm, including the upper ball joint, inwards
and change the *camber angle*, say, 1 degree to the negative. That means
I have now *reduced* by 1 degree the angle between the true vertical and
centreline of the tyre. The tyre is now more vertical than it was.
But, if I cannot change the *included angle*. I must also have also
*increased* the angle between the true vertical and the *steering axis*
through the ball joints. That 1 degree of angle didn't just disappear,
it simply moved to the other side of that line that represents true
vertical. That means I have *increased* the steering axis *inclination*
from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
it will now be 10 degrees.

What can we see from this? The wheel will be more vertical, no doubt,
since we have reduced camber. But, because the steering axis inclination
has increased, we will likely experience heavier steering. That may or
may not be noticeable. The vehicle will have more steering self
centering. Also, we are likely to get more of a camber change on the
inner wheel when the steering turns to either lock. Remember, positive
caster is playing a role in this camber change too. Will it matter? I
can't say because I have always worked within manufacturers
specifications and I can't readily visualise the kinematics of it.

The one thing you will almost certainly have done is changed the slip
angles at the front wheels because that is what camber changes to the
negative at the front wheels do. That will have, in turn, altered the
oversteer/understeer balance between the front and rear of the vehicle.
Vehicles are given positive camber at the front wheels and zero or
negative camber at the rear. That promotes understeer, a safer situation
for the average driver. By reducing caster to the minimum spec, you will
achieve a similar outcome with regard to tyre wear but will not be
dicking with the handling balance.

> When turning in a downhill thrusting turn the outer tire
> will have a negative shift in camber while the inner wheel will have a
> positive shift. The more positive caster, the more pronounced this
> "tilt" or "corner carving" tendancy. If the tires are not stiff
> enough or are underinflated, the tires will wear excessively on the
> side facing the outside of the turn. If the tires ARE stiff enough or
> inflated hard, the wear will tend to move towards the side of the tire
> on the INSIDE of the turn - tending to even the wear across the face
> of the tire.
>
> That's why my FIRST recommendation is to air up the tires, and to
> reduce the wear on the outside of the turn, possibly increase the
> negative camber. Setting the caster to the high side of the positive
> spec will give you extra negative camber on turns without any possible
> negative effects of negative camber on the straight and level. It's
> all a compromize. Dive and roll come into play along with road
> banking.
>
> a good article on camber change is here:
> https://www.hotrod.com/articles/camber-change-static-dynamic-tire-traction/.
> It is slanted towards circle track racing, but covers all the basics.
>

Yes, but it covers all the basics with a distinct *bias*. For someone
who wants to learn about the basics, it is best they look at what is
done for *road going cars* first. It is a different world with regard to
handling. Sure, progress to racing cars but do get the basics down pat
first.

For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.

[Clare Snyder]

On Wed, 19 Jun 2019 00:17:29 +1000, Xeno <xeno...@optusnet.com.au>

100%
KPI or SAI is also known as the "included angle" and is the angle
between the centerline of the steering axis and the centerline of the
wheel axis (or spindle) Without bending the pdindle assembly it
cannot be changed on modern vehicles. On older AMC and a few others
with bolt-on spindles (including SOME current FWD vehicles you CAN
change the SAI somewhat by inserting tapered shims between the knuckle
and the spindle. MOST RWD cars and a large number of FWD today do NOT
use a bolt-on spindle or a bolt-on bearing housing, making it
impossible. On the 2 part knuckles (separate knuckle and spindle) we
used to occaisionally shim them for" competition"

>If we are talking about a *King Pin* in a beam axle arrangement, the KPI
>angle is absolutely fixed and cannot be altered without recourse to
>*bending* something.

What are you thinking of bending?

>
>In terms of modern cars, however, king pins are obsolete. The last
>vehicle I can recall working on that had king pins was mid 60s.
>
>What we use now are, as you know, ball joints to anchor the steering
>knuckle yet allow multi-degree articulation. Makes the kinematics a damn
>sight easier to work out from the engineer's design viewpoint.
>
>https://www.freeasestudyguides.com/graphics/sai-sreering-axes-inclination..png
>
>In the diagram above, there is a line referencing *true vertical*,
>another referencing the SAI *angle*, and another referencing the tyre
>camber angle. The *included angle* cannot be altered. It is designed in
>and the only way to change that would be to *bend something*. In this
>case, that something would be the steering knuckle. Definitely not
>recommended but something that used to be done in vehicles of the 50s
>and 60s when you ran out of adjustment. I was fortunate I never needed
>to do that.
>

I never bent a spindle, but the flamboprough hobby stock car guys did
sometimes. It was easier to use an AMC knuckle and just shim it - no
worrying about if you got the heat treat right -- - -

>Looking at the linked diagram, if I feel the camber angle is too great,
>what options do I have. I have to move one of the ball joints in
>relation to the other. Assume the adjustment for camber is shims at the
>inner end of the top control arm. So I set to and remove sufficient
>shims to move upper control arm, including the upper ball joint, inwards
>and change the *camber angle*, say, 1 degree to the negative. That means
>I have now *reduced* by 1 degree the angle between the true vertical and
>centreline of the tyre. The tyre is now more vertical than it was.
>But, if I cannot change the *included angle*. I must also have also
>*increased* the angle between the true vertical and the *steering axis*
>through the ball joints. That 1 degree of angle didn't just disappear,
>it simply moved to the other side of that line that represents true
>vertical. That means I have *increased* the steering axis *inclination*
>from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
>it will now be 10 degrees.

No - SAI IS the included angle.
Camber IS the deviation from true vertical
SAI is measured from the spindle centerline to the steering axis and
does NOT change, even if the car is laying on it's side. You get
CAMBER CHANGE with roll and squat - but you do NOT get SAI change.

>
>What can we see from this? The wheel will be more vertical, no doubt,
>since we have reduced camber. But, because the steering axis inclination
>has increased, we will likely experience heavier steering. That may or
>may not be noticeable. The vehicle will have more steering self
>centering.

How?

Take a good look at the Turnolgy site for some good explanations.

https://www.turnology.com/tech-stories/brakes-suspension/camber-what-is-it-and-how-can-it-make-you-faster/

This IS a "handling" issue To be wearing the tires the way they are
being worn the vehicle is operating at the ragged edge of it's
handling capability on those carving downhills.

>
>For a person who is an engineer, this book is a better start point.
>https://www.springer.com/gp/book/9783319054483
>
>As a followup, this one;
>https://www.springer.com/gp/book/9783834809940
>
>I have both the above and they make for very interesting reading.

For several years my road-going car was a 1972 Vauxhall Firenza. It
had several degrees of negative caster on an unequal length control
arm suspension, and it handled like it was on rails . With the wide
Radial TA tires I had on it there was virtually NO tire wear over
almost 50,000 miles (between my driving and the friend I sold it to)

Vehicles with strut suspension require MORE negative static camber to
compensate effectively for cornering camber change

[%]

have you ever tried just driving the car

[Xeno]

In terms of the beam axle arrangement, I can see nothing that I could
satisfactorily bend in order to correct a KPI angle but, for KPI to be
out, something has to have been *bent*.

>>
>> In terms of modern cars, however, king pins are obsolete. The last
>> vehicle I can recall working on that had king pins was mid 60s.
>>
>> What we use now are, as you know, ball joints to anchor the steering
>> knuckle yet allow multi-degree articulation. Makes the kinematics a damn
>> sight easier to work out from the engineer's design viewpoint.
>>
>> https://www.freeasestudyguides.com/graphics/sai-sreering-axes-inclination..png
>>
>> In the diagram above, there is a line referencing *true vertical*,
>> another referencing the SAI *angle*, and another referencing the tyre
>> camber angle. The *included angle* cannot be altered. It is designed in
>> and the only way to change that would be to *bend something*. In this
>> case, that something would be the steering knuckle. Definitely not
>> recommended but something that used to be done in vehicles of the 50s
>> and 60s when you ran out of adjustment. I was fortunate I never needed
>> to do that.
>>
>
> I never bent a spindle, but the flamboprough hobby stock car guys did
> sometimes. It was easier to use an AMC knuckle and just shim it - no
> worrying about if you got the heat treat right -- - -

There was, IIRC, a limit to the number of degrees you could bend a
steering component *without* the application of heat. The application of
heat is always a worry because, if you get it wrong, well, shit happens.

>> Looking at the linked diagram, if I feel the camber angle is too great,
>> what options do I have. I have to move one of the ball joints in
>> relation to the other. Assume the adjustment for camber is shims at the
>> inner end of the top control arm. So I set to and remove sufficient
>> shims to move upper control arm, including the upper ball joint, inwards
>> and change the *camber angle*, say, 1 degree to the negative. That means
>> I have now *reduced* by 1 degree the angle between the true vertical and
>> centreline of the tyre. The tyre is now more vertical than it was.
>> But, if I cannot change the *included angle*. I must also have also
>> *increased* the angle between the true vertical and the *steering axis*
>> through the ball joints. That 1 degree of angle didn't just disappear,
>> it simply moved to the other side of that line that represents true
>> vertical. That means I have *increased* the steering axis *inclination*
>>from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
>> it will now be 10 degrees.
>
> No - SAI IS the included angle.

Please, be informed that SAI is the angle through the steering axis
relative to the *true vertical*. The true vertical is the *vertical
reference*, an imaginary line drawn at right angles to the road surface.
It will always *remain* at right angles to the road surface regardless
of what is done to the SAI *angle* and/or the camber angle. The
*included angle*, by its very name, *includes* the SAI angle *and* the
camber angle. The included angle is designed in and cannot be changed by
normal means. The included angle is a diagnosis angle and, if deviated
from specifications, indicates that the steering knuckle has suffered
damage, ie bent steering knuckle.

https://www.waybuilder.net/free-ed/SkilledTrades/Automotive/09AdvWheelAlign/09AdvWheelPics/09AdvW69.jpg

Do not be deceived by the angle at which the stub axle is drawn on the
above linked diagram. To be true to reality, the stub axle should have
been drawn at right angles to the blue centreline of the *wheel*. The
dotted blue line is not referencing anything on that diagram apart from
the horizontal datum line representing the road.

> Camber IS the deviation from true vertical

We agree on one point at least. Yes, camber is the deviation from true
vertical. What we have, however, is a dispute regarding true vertical
and what it is referencing.

> SAI is measured from the spindle centerline to the steering axis and

Correction, it not a reference to the spindle centreline, it is
referencing true vertical. The only point that doesn't change is the
true vertical since it is a vertical reference to the ground upon which
the vehicle is sitting and is at a *right angle* to it.

> does NOT change, even if the car is laying on it's side. You get
> CAMBER CHANGE with roll and squat - but you do NOT get SAI change.

If any steering axis *pivot* point moves laterally in relation to the
other pivot point, there will be a change in SAI relative to the true
vertical. There simply has to be. The included angle, since it is
*fixed* by design, cannot change. IOW, the angular relationship the
steering axis has with the camber angle is permanently fixed. The
included angle's relationship with the true vertical, however, is not fixed.

>>
>> What can we see from this? The wheel will be more vertical, no doubt,
>> since we have reduced camber. But, because the steering axis inclination
>> has increased, we will likely experience heavier steering. That may or
>> may not be noticeable. The vehicle will have more steering self
>> centering.
>
> How?

Any increase in SAI causes a commensurate increase in steering self
centering.

>
> Take a good look at the Turnolgy site for some good explanations.
>
> https://www.turnology.com/tech-stories/brakes-suspension/camber-what-is-it-and-how-can-it-make-you-faster/

We aren't looking at camber making a car faster. We are looking at
camber, under the influence of positive caster, making tyres wear on the
outside edge under severe steering lock situations at *low speed*.

Um, no it is not. It is entirely *normal* given the nature of the
vehicle operation. Let me excerpt a snippet from an old text I used to
use when teaching this stuff;

Caster Angle Tire Wear
The caster angle is generally considered to be a nontire wearing angle.
Although this statement is true, unequal or *excessive* caster can
*indirectly* cause tire wear. When the front wheels are turned on a
vehicle with a lot of positive caster, the front wheels become angled,
called camber *roll*. (The caster angle is a measurement of the
difference in camber angle from when the wheel is turned inward to when
the wheel is turned outward.) Many vehicle manufacturers have positive
caster designed into the suspension system. This positive caster has
increased the directional stability of these vehicles. However, if the
vehicle is used exclusively in city-type driving, the positive caster
can cause wear to the outside shoulders of both front tyres.
Automotive Chassis Systems, Brakes, Steering, Suspension and Alignment
James D. Halderman, 1996, Prentice Hall Inc.

This text is in full agreement with my diagnosis of Arlen's issue. His
issue is *camber Scrub* causes by *Camber Roll* during *tight turns* as
evidenced by the specific type of longitudinal feathering he is
experiencing on the outer shoulder of his tyres. It also supports the
partial solution that I offered, that he reduce his caster to the
minimum allowable specification. I have *known* of this issue for
*decades* but my current Toyota has given me my first personal
experience with it.

>>
>> For a person who is an engineer, this book is a better start point.
>> https://www.springer.com/gp/book/9783319054483
>>
>> As a followup, this one;
>> https://www.springer.com/gp/book/9783834809940
>>
>> I have both the above and they make for very interesting reading.
>
> For several years my road-going car was a 1972 Vauxhall Firenza. It
> had several degrees of negative caster on an unequal length control

Negative caster is unusual on a RWD car since it has the nasty effect of
increasing body roll, highly undesirable. Negative caster is more usual
on a FWD because of drive torque as opposed to rolling resistance but it
is kept to a bare minimum. It would be interesting to see all the
steering geometry specifications for that vehicle.

> arm suspension, and it handled like it was on rails . With the wide

I presume you mean SLA front suspension.

> Radial TA tires I had on it there was virtually NO tire wear over
> almost 50,000 miles (between my driving and the friend I sold it to)

That will depend entirely on the type of driving you do. If it's a lot
of highway driving, no problem. Light urban driving, again no problem.
Our previous Toyota didn't show an issue but it was in an urban
environment most of its life. If you have lots of tight turns, as I have
experienced here and Arlen has experienced, you get camber scrub. It is
the compromise the manufacturers had to make given typical vehicle usage
patterns. Arlen's usage is not typical since he is doing lots of full
lock turns, grade notwithstanding. It is the full lock turns, with
attendant high positive camber gain on the inner wheel, that do the damage.

[Arlen G. Holder]

On Wed, 19 Jun 2019 13:26:36 +1000, Xeno wrote:

> We aren't looking at camber making a car faster. We are looking at
> camber, under the influence of positive caster, making tyres wear on the
> outside edge under severe steering lock situations at *low speed*.

Hi Xeno,
I agree with this special case, which most descriptions on the net ignore
since they're looking at racing versus nominally around 30mph.

Today I counted the steering wheel degrees, where on many turns it was only
90 degrees to the left and 90 degrees to the right, and on plenty others it
was 180 to the left or right, and on about 10% of the turns, it was more
than 360, where the biggest turns were more than 360 plus 90, and the less
biggest turns were slightly less than that, at about 375 degrees turning
the steering wheel.

I also hung a redneck lateral 'accelerometer' on the mirror, which was
simply the USB cable for the phone looped over the mirror, where it swung
from side to side constantly, but at about 45 degrees or less most of the
time. <https://i.postimg.cc/L6CN5SKm/mount30.jpg>

While it was hard to snap photos since one hand had to be on the steering
wheel, I had expected the loop of USB cable to swing further than 45
degrees but most of the time it seemed LESS than 45 degrees, I guess
because the speeds are so slow?

[Clare Snyder]

On Wed, 19 Jun 2019 13:26:36 +1000, Xeno <xeno...@optusnet.com.au>

You are right. It's been 36 years since I taught the stuff and 30
since I did it.

YUes and no. He's not going down the hill fast - but if he went down
the hill much faster, he would not be staying on the road because he
is reaching the limit where the tire will just "let go" instead of
scuffing.

I used to teach the stuff too. I used to do the alignments, and I
used to drive competitively

>Caster Angle Tire Wear
>The caster angle is generally considered to be a nontire wearing angle.
>Although this statement is true, unequal or *excessive* caster can
>*indirectly* cause tire wear. When the front wheels are turned on a
>vehicle with a lot of positive caster, the front wheels become angled,
>called camber *roll*.

Just look at a road grader

> (The caster angle is a measurement of the
>difference in camber angle from when the wheel is turned inward to when
>the wheel is turned outward.) Many vehicle manufacturers have positive
>caster designed into the suspension system. This positive caster has
>increased the directional stability of these vehicles. However, if the
>vehicle is used exclusively in city-type driving, the positive caster
>can cause wear to the outside shoulders of both front tyres.
>Automotive Chassis Systems, Brakes, Steering, Suspension and Alignment
>James D. Halderman, 1996, Prentice Hall Inc.

I used Glenn's Automobile Engine Rebuilding and Maintenance,
Stockel's Auto Mechanic Fundamentals, and Crouse's Automotive
Mechanics. Also had a text on handling and suspension - can't remember
who wrote it or what it was called. It's LONG gone, it appears.

ANyway - from Modern Tire Dealer: Jan 2002 edition -

If the vehicle is normally, or routinely, driven under changing
lateral conditions (on curvy, twisty roads or on a road course), the
alignment angles will require a bias toward negative camber. When the
vehicle enters a turn, centrifugal force naturally moves the weight
mass toward the outside of the vehicle (if turning right, weight is
moved to the left; if turning left, mass momentum moves toward the
right). This causes the tires to flex both downward (pushing the tire
section toward the pavement) and laterally (to the outside, causing
the sidewall to allow the tire to lean).

If the static camber was set at zero, for example, a hard right turn
might cause the outside shoulder of the left front tire to bear the
brunt of the weight and scrubbing action, while a large percentage of
that tire´s center and inside tread area is lifted off the pavement.
The result: You´re only using a very tiny portion of the tread
(traction capability), while placing isolated wear on the outer
shoulder. This causes lousy handling in the turns and tires with
worn-out outer shoulders.

In order to compensate for this type of driving (lots of left/right
turns), we adjust the camber angle accordingly in order to benefit
from maximum tread contact in those turns. Once again, our goal is
simply to create a maximum tread contact patch under the vehicle´s
"typical" operating conditions.


Also see:

https://dsportmag.com/the-tech/extracting-handling-performance-alignment-settings/

See the section "effects of camber settings"

Also see:
https://www.youtube.com/watch?v=6Lnb7iQ1NJs

From Allpar - on alignment for early Mopars they have THIS to say:
Camber’s a whole different ball game. The factory never recommended
negative camber at all. (It’s negative when the top of the wheel tilts
in.) They had a good reason for this: they were trying to minimize
tire wear. With bias ply tires, camber is critical. Tilt the top in a
bit, and the inner edge of the skin will wear out—fast. With steel
belted radials, this is much less of a factor. Of course, there’s lots
of other factors at work here: how stiff are the sidewalls? How much
air pressure do you run? How low is the aspect ratio (profile)? All of
these factors can affect the “best” (if there is such a thing) camber
number for you. If you have superlow- profile tires (like 40 series),
you might want a tad less camber. Ditto for high air pressures and/or
stiff sidewalls. You always (always) want at least a some negative
camber. Even with granny driving, there will be that emergency, kid
chasing a ball, etc., requiring an evasive maneuver. Having more
cornering G force at your disposal—via the more complete
tread/pavement contact afforded by the “preload” that negative camber
generates— is always a good thing.


The settings recommended and designed in to the vehicle are a
compromize - designed for acceptable handling and tire wear under
"normal" conditions. Same with tire pressures.

Under "abnormal" conditions - nose down, tight corners : you get both
squat and roll causing the camber to go positive - and you get weight
shift to the outside front corner, loading the outside front tire
significantly more than leveland straight driving - REQUIRING ahigher
tire pressure to "support" the load. It's the same as throwing 600
pounds into the trunk - only in reverse.


Regardless of the terminol;ogy (and I WAS wrong - and I admit it) the
SIMPLEST and MOST EFFECTIVE steps to reduce the tire wear are:

#1 -check tire inflation and increase the front tire pressures -
basically to the spec for the rear tires fully loaded. - generally
about 5 to 10 PSI over the normal recommended tire pressure.
#2 - adjust the camber to 1 to 1.5 degrees more negative than spec if
possible.

>This text is in full agreement with my diagnosis of Arlen's issue. His
>issue is *camber Scrub* causes by *Camber Roll* during *tight turns* as
>evidenced by the specific type of longitudinal feathering he is
>experiencing on the outer shoulder of his tyres. It also supports the
>partial solution that I offered, that he reduce his caster to the
>minimum allowable specification. I have *known* of this issue for
>*decades* but my current Toyota has given me my first personal
>experience with it.

Not dissagreeing with your diagnosis

And I've dealt with it for years.About 90% of cars on the road are
running underinflated tires. PERHAPS just running the recommended
pressure may reduce the problem - IF the owner is allowing the
pressures to run too low - but a few extra PSI will NOT hurt - and
WILL help. I tend to drive a bit agressively - not as much as when
Iwas 50 years younger - and I ALWAYS run my front tires about 5 PSI
over spec - to prevent wearing the outer shoulders off my tires.

>>>
>>> For a person who is an engineer, this book is a better start point.
>>> https://www.springer.com/gp/book/9783319054483
>>>
>>> As a followup, this one;
>>> https://www.springer.com/gp/book/9783834809940
>>>
>>> I have both the above and they make for very interesting reading.
>>
>> For several years my road-going car was a 1972 Vauxhall Firenza. It
>> had several degrees of negative caster on an unequal length control

Sorry - I meant negative CAMBER

>
>Negative caster is unusual on a RWD car since it has the nasty effect of
>increasing body roll, highly undesirable. Negative caster is more usual
>on a FWD because of drive torque as opposed to rolling resistance but it
>is kept to a bare minimum. It would be interesting to see all the
>steering geometry specifications for that vehicle.
>
>> arm suspension, and it handled like it was on rails . With the wide
>
>I presume you mean SLA front suspension.

Yes - short and long arm

>
>> Radial TA tires I had on it there was virtually NO tire wear over
>> almost 50,000 miles (between my driving and the friend I sold it to)
>
>That will depend entirely on the type of driving you do. If it's a lot
>of highway driving, no problem. Light urban driving, again no problem.

Pretty agressive driving - - It had a 2300cc OHC engine with twin
CD175 Strombergs. I rallied it a couple times when the Renault wasn't
ready to go. I also chased it up and down Mount Washington and around
the Cabot Trail. I lent tit to my best man when his Lotus Cortina was
out of commission. Guys with Lotus Cortinas didn't generally baby
them.

The negative scrub radius helped tire wear and handling too, I
suspect. - - -

>Our previous Toyota didn't show an issue but it was in an urban
>environment most of its life. If you have lots of tight turns, as I have
>experienced here and Arlen has experienced, you get camber scrub. It is
>the compromise the manufacturers had to make given typical vehicle usage
>patterns. Arlen's usage is not typical since he is doing lots of full
>lock turns, grade notwithstanding. It is the full lock turns, with
>attendant high positive camber gain on the inner wheel, that do the damage.

Along with the forward weight transfer and the centrifugal force
loading the outer tire. - and I agree - high positive camber gain -
not only from the tight lock, but also the squat and roll.

[Clare Snyder]

use a "g" meter app on your phone to check your lateral g-force.
Then check the deceleration G force going into the turn, and along
with the downhill slope, calculate the load on that outer front tire.
It WILL surprize you. Then check the required tire pressure for that
load - - - - - - - - - - - I'm guessing the load on that tire will be
approaching (or very possibly exceding) the static level load.

[Xeno]

On 19/6/19 2:50 pm, Arlen G. Holder wrote:
> On Wed, 19 Jun 2019 13:26:36 +1000, Xeno wrote:
>
>> We aren't looking at camber making a car faster. We are looking at
>> camber, under the influence of positive caster, making tyres wear on the
>> outside edge under severe steering lock situations at *low speed*.
>
> Hi Xeno,
> I agree with this special case, which most descriptions on the net ignore
> since they're looking at racing versus nominally around 30mph.

Indeed, it is quite noticeable by its absence on the net. I suspect
that's because the number of people affected as much as you are is quite
minimal. I did once find a good description of it with pictures
describing the type of feathering but that seems to have vanished as has
a video that described exactly what happened during sharp cornering vis
a vis camber angles. I could have used a video like that in my teaching
days. That said, we had the teaching model that was used in the video, a
steering knuckle setup mounted on a bench, so I could have made the
video myself had I the time.

>
> Today I counted the steering wheel degrees, where on many turns it was only
> 90 degrees to the left and 90 degrees to the right, and on plenty others it
> was 180 to the left or right, and on about 10% of the turns, it was more
> than 360, where the biggest turns were more than 360 plus 90, and the less
> biggest turns were slightly less than that, at about 375 degrees turning
> the steering wheel.

Yep, it's those full lock turns at low speed that does it. The vehicle
manufacturer has had to make a compromise here and you are at the wrong
end of his compromise.

>
> I also hung a redneck lateral 'accelerometer' on the mirror, which was
> simply the USB cable for the phone looped over the mirror, where it swung
> from side to side constantly, but at about 45 degrees or less most of the
> time. <https://i.postimg.cc/L6CN5SKm/mount30.jpg>
>
> While it was hard to snap photos since one hand had to be on the steering
> wheel, I had expected the loop of USB cable to swing further than 45
> degrees but most of the time it seemed LESS than 45 degrees, I guess
> because the speeds are so slow?
>

[Xeno]

In my case, 18 years since I both taught and did it. 18 years also since
I last had access to the latest version of a computerised 4 wheel
aligner and a full steering, suspension and brake shop. I really miss
that access.

What you need to keep in mind here is that, with a decent amount of
positive caster, the wheel on the outside of the bend goes more vertical
due to camber roll, the opposite of what the wheel on the inside of the
bend is doing. It is, in effect, losing camber so it will not be riding
hard on the edges of its tyres. That is what it needs to do to maintain
a full tyre contact patch and resist the G Forces in the turn. The inner
tyre isn't so fortunate, it gains heaps of positive camber, loses the
contact patch on the inner edges of the tread and scuffs much more.

I wasn't a competition driver. I was a pit crew member in a stock car
racing team at one time. That was over 40 years ago when I was young and
single.

>> Caster Angle Tire Wear
>> The caster angle is generally considered to be a nontire wearing angle.
>> Although this statement is true, unequal or *excessive* caster can
>> *indirectly* cause tire wear. When the front wheels are turned on a
>> vehicle with a lot of positive caster, the front wheels become angled,
>> called camber *roll*.
>
> Just look at a road grader

A road grader is a different kettle of fish. Their steering is much more
flexible in its control than the average car. It needs to be in order to
provide a bias against the action of the blade. For instance, they can
*tilt* both steering wheels in the same direction.

>
>> (The caster angle is a measurement of the
>> difference in camber angle from when the wheel is turned inward to when
>> the wheel is turned outward.) Many vehicle manufacturers have positive
>> caster designed into the suspension system. This positive caster has
>> increased the directional stability of these vehicles. However, if the
>> vehicle is used exclusively in city-type driving, the positive caster
>> can cause wear to the outside shoulders of both front tyres.
>> Automotive Chassis Systems, Brakes, Steering, Suspension and Alignment
>> James D. Halderman, 1996, Prentice Hall Inc.
>
> I used Glenn's Automobile Engine Rebuilding and Maintenance,
> Stockel's Auto Mechanic Fundamentals, and Crouse's Automotive
> Mechanics. Also had a text on handling and suspension - can't remember
> who wrote it or what it was called. It's LONG gone, it appears.
>

I used Stockel when I was an apprentice. That was a very long time ago
and it was very good on the fundamentals. At the college we used an
Aussie version of Crouse's text, in collaboration with Ed May. Still
have the 2 volume 5th edition that was current when I retired from
teaching. I recently gave away the much earlier edition I had to a
friend who restores the kinds of cars covered by that book. As for
engine rebuilding, the go to reference in this country was the Repco
Engine Manual. I had two copies of that, gave the older version away to
the same friend mentioned above.
I still have quite a few books on suspensions, steering & handling;
Chassis Engineering, Herb Adams
The Race Car Chassis, Forbes Aird
How To Make Your Car Handle, Fred Puhn
Racing Car Design & Development, Len Terry, Alan Baker
Chassis Tuning, Jan P Norbye
Design Of racing Sports Cars, Colin Campbell
Automobile Suspensions, Colin Campbell
New Directions In Suspension Design, Colin Campbell
The Sports Car - Its Design and Performance, Colin Campbell
Car Suspension At Work, Jeffrey Daniels
Competition Car Suspension, Allan Staniforth

I have several more but the above are the ones more focused on the
performance and handling side of vehicles rather than the fundamental
principles. Most are getting rather long in the tooth now and don't
adequately reflect current trends.

> ANyway - from Modern Tire Dealer: Jan 2002 edition -
>
> If the vehicle is normally, or routinely, driven under changing
> lateral conditions (on curvy, twisty roads or on a road course), the
> alignment angles will require a bias toward negative camber. When the
> vehicle enters a turn, centrifugal force naturally moves the weight
> mass toward the outside of the vehicle (if turning right, weight is
> moved to the left; if turning left, mass momentum moves toward the
> right). This causes the tires to flex both downward (pushing the tire
> section toward the pavement) and laterally (to the outside, causing
> the sidewall to allow the tire to lean).
>
> If the static camber was set at zero, for example, a hard right turn
> might cause the outside shoulder of the left front tire to bear the
> brunt of the weight and scrubbing action, while a large percentage of
> that tire´s center and inside tread area is lifted off the pavement.
> The result: You´re only using a very tiny portion of the tread
> (traction capability), while placing isolated wear on the outer
> shoulder. This causes lousy handling in the turns and tires with
> worn-out outer shoulders.

I have no issue with that but the type of feathered edge on Arlen's
vehicle indicated to me that it wasn't a pure camber issue.

What they don't say is that negative camber will decrease the slip angle
at the front wheels whilst leaving the rear as standard. That will lead
to a snap oversteering car and *granny* may find that more than a little
disconcerting.

>
> The settings recommended and designed in to the vehicle are a
> compromize - designed for acceptable handling and tire wear under
> "normal" conditions. Same with tire pressures.

Always. You can change the understeer/oversteer balance with tyre
pressures alone.

>
> Under "abnormal" conditions - nose down, tight corners : you get both
> squat and roll causing the camber to go positive - and you get weight
> shift to the outside front corner, loading the outside front tire
> significantly more than leveland straight driving - REQUIRING ahigher
> tire pressure to "support" the load. It's the same as throwing 600
> pounds into the trunk - only in reverse.
>
>
> Regardless of the terminol;ogy (and I WAS wrong - and I admit it) the
> SIMPLEST and MOST EFFECTIVE steps to reduce the tire wear are:
>
> #1 -check tire inflation and increase the front tire pressures -
> basically to the spec for the rear tires fully loaded. - generally
> about 5 to 10 PSI over the normal recommended tire pressure.
> #2 - adjust the camber to 1 to 1.5 degrees more negative than spec if
> possible.
>
>> This text is in full agreement with my diagnosis of Arlen's issue. His
>> issue is *camber Scrub* causes by *Camber Roll* during *tight turns* as
>> evidenced by the specific type of longitudinal feathering he is
>> experiencing on the outer shoulder of his tyres. It also supports the
>> partial solution that I offered, that he reduce his caster to the
>> minimum allowable specification. I have *known* of this issue for
>> *decades* but my current Toyota has given me my first personal
>> experience with it.
>
> Not dissagreeing with your diagnosis

Thanks for that.

>
> And I've dealt with it for years.About 90% of cars on the road are
> running underinflated tires. PERHAPS just running the recommended
> pressure may reduce the problem - IF the owner is allowing the
> pressures to run too low - but a few extra PSI will NOT hurt - and
> WILL help. I tend to drive a bit agressively - not as much as when
> Iwas 50 years younger - and I ALWAYS run my front tires about 5 PSI
> over spec - to prevent wearing the outer shoulders off my tires.
>>>>
>>>> For a person who is an engineer, this book is a better start point.
>>>> https://www.springer.com/gp/book/9783319054483
>>>>
>>>> As a followup, this one;
>>>> https://www.springer.com/gp/book/9783834809940
>>>>
>>>> I have both the above and they make for very interesting reading.
>>>
>>> For several years my road-going car was a 1972 Vauxhall Firenza. It
>>> had several degrees of negative caster on an unequal length control
>
> Sorry - I meant negative CAMBER

Ah, that explains it then.

>>
>> Negative caster is unusual on a RWD car since it has the nasty effect of
>> increasing body roll, highly undesirable. Negative caster is more usual
>> on a FWD because of drive torque as opposed to rolling resistance but it
>> is kept to a bare minimum. It would be interesting to see all the
>> steering geometry specifications for that vehicle.
>>
>>> arm suspension, and it handled like it was on rails . With the wide
>>
>> I presume you mean SLA front suspension.
> Yes - short and long arm
>>
>>> Radial TA tires I had on it there was virtually NO tire wear over
>>> almost 50,000 miles (between my driving and the friend I sold it to)
>>
>> That will depend entirely on the type of driving you do. If it's a lot
>> of highway driving, no problem. Light urban driving, again no problem.
>
> Pretty agressive driving - - It had a 2300cc OHC engine with twin
> CD175 Strombergs. I rallied it a couple times when the Renault wasn't
> ready to go. I also chased it up and down Mount Washington and around
> the Cabot Trail. I lent tit to my best man when his Lotus Cortina was
> out of commission. Guys with Lotus Cortinas didn't generally baby
> them.

The Vauxhall Firenza never made it to these shores. I see it had a very
brief life - 3 years.

>
> The negative scrub radius helped tire wear and handling too, I
> suspect. - - -

Definitely a safer way to go!

>> Our previous Toyota didn't show an issue but it was in an urban
>> environment most of its life. If you have lots of tight turns, as I have
>> experienced here and Arlen has experienced, you get camber scrub. It is
>> the compromise the manufacturers had to make given typical vehicle usage
>> patterns. Arlen's usage is not typical since he is doing lots of full
>> lock turns, grade notwithstanding. It is the full lock turns, with
>> attendant high positive camber gain on the inner wheel, that do the damage.
>
> Along with the forward weight transfer and the centrifugal force
> loading the outer tire. - and I agree - high positive camber gain -
> not only from the tight lock, but also the squat and roll.

Most suspensions systems have a fair degree of anti-dive geometry built
into them these days so it's not the problem it was. Positive caster
jacks up the outer wheel so that should counter it as well.

Suspension systems, the SLA in particular, allow (cause) the front
camber to change under deflection. With an SLA front suspension at
normal ride height, the camber is at its static setting. Assume its
static setting is 0, neither negative or positive. As the wheel is
deflected up over a bump, the short arm will track a smaller radius than
the longer lower arm. This means the upper ball joint will be pulled
inwards at a greater rate than the lower ball joint. Because of this,
the camber actually goes more negative as the suspension is deflected
upwards. The benefit of this is that track width doesn't change under
single or two wheel deflection since the tyre at the contact patch
maintains its fore and aft alignment. Under body roll in a turn, the
inner mount of the upper arm may track outwards. This would normally
cause a camber change to the positive but, because of the short arm's
negative effect on camber change, the effect of each cancels the other
out and camber remains at or close to the static setting. IOW, the wheel
remains close to vertical and the contact patch and slip angles are
minimally affected. This is one of the reasons the racing fraternity
prefer SLA suspensions in either 4 link or 5 link varieties.

https://www.imperial.ac.uk/news/image/mainnews2012/21320.jpg

Note too that the action depicted above by the SLA suspension is in
straight ahead situations. It does not take into account any camber roll
that occurs when the wheel is in a tight turn which, if the outside
wheel is already at a neutral camber, will cause it to become decidedly
negative.

One thing I have learnt about steering and suspensions over the years,
the more you learn, the more you realise you don't know.

[Clare Snyder]

On Wed, 19 Jun 2019 21:48:30 +1000, Xeno <xeno...@optusnet.com.au>

wrote:

>On 19/6/19 2:51 pm, Clare Snyder wrote:
>> On Wed, 19 Jun 2019 13:26:36 +1000, Xeno <xeno...@optusnet.com.au>
>> wrote:
>>
>>> On 19/6/19 4:27 am, Clare Snyder wrote:
>>>> On Wed, 19 Jun 2019 00:17:29 +1000, Xeno <xeno...@optusnet.com.au>
>>>> wrote:
>
>I have several more but the above are the ones more focused on the
>performance and handling side of vehicles rather than the fundamental
>principles. Most are getting rather long in the tooth now and don't
>adequately reflect current trends.
>

If I had a need to "design" a suspension system I'd just ask my
good friend Gary who has forgotten more than I ever knew about
performance suspension and chassis. When it comes to figuring out
what's wrong with an existing vehicle for a given application I've had
a pretty good record at sorting it out.

>
>> ANyway - from Modern Tire Dealer: Jan 2002 edition -
>>
>> If the vehicle is normally, or routinely, driven under changing
>> lateral conditions (on curvy, twisty roads or on a road course), the
>> alignment angles will require a bias toward negative camber. When the
>> vehicle enters a turn, centrifugal force naturally moves the weight
>> mass toward the outside of the vehicle (if turning right, weight is
>> moved to the left; if turning left, mass momentum moves toward the
>> right). This causes the tires to flex both downward (pushing the tire
>> section toward the pavement) and laterally (to the outside, causing
>> the sidewall to allow the tire to lean).
>>
>> If the static camber was set at zero, for example, a hard right turn
>> might cause the outside shoulder of the left front tire to bear the
>> brunt of the weight and scrubbing action, while a large percentage of
>> that tire´s center and inside tread area is lifted off the pavement.
>> The result: You´re only using a very tiny portion of the tread
>> (traction capability), while placing isolated wear on the outer
>> shoulder. This causes lousy handling in the turns and tires with
>> worn-out outer shoulders.
>
>I have no issue with that but the type of feathered edge on Arlen's
>vehicle indicated to me that it wasn't a pure camber issue.

Is there ever a "pure" anything issue???

You are worried about "snap oversteer" at under 30 MPH - - - -

>> The settings recommended and designed in to the vehicle are a
>> compromize - designed for acceptable handling and tire wear under
>> "normal" conditions. Same with tire pressures.
>
>Always. You can change the understeer/oversteer balance with tyre
>pressures alone.

Which is why I recommended tire pressure check FIRST.

The USA got the Opel - we got the Vauxhall. Whether sold as a Viva HC
or a Firenza it was the same car. Also sold as the Magnum in the UK

And the sla suspension is designed to do what I am recommending to do
- but just not enough for THIS situation. By starting with a static
negative you are just helping the factory design do a better job.

>
>https://www.imperial.ac.uk/news/image/mainnews2012/21320.jpg
>
>Note too that the action depicted above by the SLA suspension is in
>straight ahead situations. It does not take into account any camber roll
>that occurs when the wheel is in a tight turn which, if the outside
>wheel is already at a neutral camber, will cause it to become decidedly
>negative.
>

Which is what you want - and adding an extra 1.5 degrees or so can
only help

>One thing I have learnt about steering and suspensions over the years,
>the more you learn, the more you realise you don't know.

"If I knew then what I know now I wouldn't know what I know now"

[Xeno]

On 20/6/19 7:42 am, Clare Snyder wrote:
> On Wed, 19 Jun 2019 21:48:30 +1000, Xeno <xeno...@optusnet.com.au>
> wrote:
>
>> On 19/6/19 2:51 pm, Clare Snyder wrote:
>>> On Wed, 19 Jun 2019 13:26:36 +1000, Xeno <xeno...@optusnet.com.au>
>>> wrote:
>>>
>>>> On 19/6/19 4:27 am, Clare Snyder wrote:
>>>>> On Wed, 19 Jun 2019 00:17:29 +1000, Xeno <xeno...@optusnet.com.au>
>>>>> wrote:
>>
>> I have several more but the above are the ones more focused on the
>> performance and handling side of vehicles rather than the fundamental
>> principles. Most are getting rather long in the tooth now and don't
>> adequately reflect current trends.
>>
> If I had a need to "design" a suspension system I'd just ask my
> good friend Gary who has forgotten more than I ever knew about
> performance suspension and chassis. When it comes to figuring out
> what's wrong with an existing vehicle for a given application I've had
> a pretty good record at sorting it out.

My point in referring to those books on performance chassis and
suspension systems is that it gives you insight into why things are
designed in the way they are on *road going cars* by comparing them to
what the racers do. The design decisions are way different, not only
because the environment is different but also because the race drivers
are much more attuned to the handling of their cars. What is more, those
drivers will know how to tweak their car's handling to suit their own
personal preference.

When the designers get it wrong, they do it spectacularly. The A Class
Benz, when it was first released, was just such a cockup. In the Moose
Test, it *fell over*. The natural roll resonance frequency of the rear
suspension in the A Class near enough coincided with the 4 yaw reversals
in the Elk Test so that each directional change *added* further to the
toppling force until it became large enough to tip the car beyond the
fulcrum of its outer tyre contact patches. It takes very precise
counter-steering to correct such a thing *in real time* and the Benz
solution was a number of modifications. The first was to modify the
suspension by uprating spring and damper frequencies which increased the
natural rolling frequency. That reduced the yaw enhancement coincidence
effect but, because of extremes of loading between empty and full,
didn't entirely remove it under all circumstances. Remember, the A Class
did the Elk Test with a *full load*. The rear track was widened, this
then required a greater side force to tip the car over. A stiffer front
anti-roll bar was fitted which increased understeer but also reduced the
tendency to tail swing in lane changing manoeuvres. This increased front
tyre slip angles and rolling resistance thus causing the car to slow
more quickly. The tyres were standardised at 195/50-15 instead of the
original 175/65-15. These had a 10mm smaller rolling diameter lowering
both the roll centre and CofG but also, to the negative, increased
slightly the critical overturning moment. There were most likely other
kinematic changes made to the front and rear suspensions and, though I
can take an educated guess as to where these might have been made, I
have seen no further detail concerning them. As a finale, stability
control was fitted *as standard*, which Benz call ESP, and the precise
braking reactions that the ESP gave, which in turn provided precise
counter steering, finally solved the issue.

https://www.carsifu.my/news/cars-are-safer-today-thanks-to-mercedes-benzs-infamous-elk-test

In the hands of a racing car driver, the A class, in its original form,
would likely not have rolled on the Moose Test. The target market
however was not racing car drivers. In the hands of an average driver,
the A Class was potentially lethal. The primary error was in the natural
roll resonance frequency. All the Benz engineers were trying to do was
improve the ride quality but, in doing so, created an unintended
consequence. What was worse though was that the issue was not discovered
in testing. Obviously their testing regime was insufficiently broad.

I was trained as a mechanic, not a design engineer, so I could quite
easily have modified a car with different springs and created such a
scenario as befell the A Class.
This book; https://www.sae.org/publications/books/content/r-114/
was one I purchased a very long time ago soon after it was published.
This and others subsequently enabled me to gain the insight that I
needed in order to alert apprentices of the unintended consequences of
their car modifications by better understanding vehicle dynamics. A
simple example is the lowering of a car by use of shorter coils. It
upsets the kinematics of the suspension and you get unintended
consequences such as described in this video clip.
https://www.whiteline.com.au/roll_centre_kits.php
When I was teaching apprentices, the internet was not the vast resource
that it is today and their reference material did not extend to such
esoteric areas as vehicle dynamics. Even now, if you scan though
training texts for mechanics, you find information on steering and
suspensions sparse beyond the basics needed to service and repair them.

>>
>>> ANyway - from Modern Tire Dealer: Jan 2002 edition -
>>>
>>> If the vehicle is normally, or routinely, driven under changing
>>> lateral conditions (on curvy, twisty roads or on a road course), the
>>> alignment angles will require a bias toward negative camber. When the
>>> vehicle enters a turn, centrifugal force naturally moves the weight
>>> mass toward the outside of the vehicle (if turning right, weight is
>>> moved to the left; if turning left, mass momentum moves toward the
>>> right). This causes the tires to flex both downward (pushing the tire
>>> section toward the pavement) and laterally (to the outside, causing
>>> the sidewall to allow the tire to lean).
>>>
>>> If the static camber was set at zero, for example, a hard right turn
>>> might cause the outside shoulder of the left front tire to bear the
>>> brunt of the weight and scrubbing action, while a large percentage of
>>> that tire´s center and inside tread area is lifted off the pavement.
>>> The result: You´re only using a very tiny portion of the tread
>>> (traction capability), while placing isolated wear on the outer
>>> shoulder. This causes lousy handling in the turns and tires with
>>> worn-out outer shoulders.
>>
>> I have no issue with that but the type of feathered edge on Arlen's
>> vehicle indicated to me that it wasn't a pure camber issue.
>
> Is there ever a "pure" anything issue???

No but, as stated, that particular feathered tread effect was pretty
unequivocal as to its cause.

No but the car you correct for 30 MPH behaviour can easily become a pig
at 60 or 70 MPH. That's when the snap oversteer becomes a concern.

This camber scrub issue comes about because people want steering
stability at speed. Can't blame them for that and can't blame the
manufacturers for biasing their designs that way, especially when only a
very small percentage of drivers are going to see the extreme effects
that Arlen is seeing. My Toyota has it but not to any extent that I'm
going to swap tyres around on rims or anything like that. I'll just
replace the tyres a tad earlier than I usually do. I managed to get only
60,000 kilometres out of the first set where I would have expected my
more usual 80,000 kilometres that I was getting from previous Toyotas.
It's no big deal. What I did do is change my route slightly so I travel
a little further on my daily run but don't have to negotiate more than
one tight roundabout and rather more gentle bends. That little bit of
extra distance sure aggravates my wife though! ;-)

Yep, badgework engineering. In that era we had Isuzus dressed up as our
local GM products.

[Arlen G. Holder]

On Fri, 21 Jun 2019 01:11:25 +1000, Xeno wrote:

> No but, as stated, that particular feathered tread effect was pretty
> unequivocal as to its cause.

I thank you, Xeno (and Clare) for UNDERSTANDING my particular issue.

I'm not actively participating simply because I'm embarrassed that I can't
add any additional value, in that I can _read_ what Xeno (and Clare) say,
and I can understand what they say, but when I've been driving the road
daily (multiple times), I keep trying to _imagine_ what is happening, while
I'm taking those turns with steering wheel inputs of
o Mostly 90 degrees each way (some less, some more)
o Some almost 360 steering wheel inputs
o Some even 90 degrees more than 360 degree steering inputs
All at around 20, to 30, to 40 (but no higher) speeds.

I did air up the tires, in an attempt to keep the tread more "firm", where
I will check front camber & caster separately (I need the tools first).

I picked up what seems to be a great free accelerometer graphical tool
o Sensors Multitool, version 1.3.2, by Wered Software
<https://play.google.com/store/apps/details?id=com.wered.sensorsmultitool>

Here's a screenshot of the output on my Android device but I need to test
it further before making any "lateral acceleration" claims ... where I'm
not sure exactly yet how to test other than to put the phone on the seat as
I drive downhill (uphill seems to have lesser forces for some reason).
<https://i.postimg.cc/7hPhBY5b/accelerate01.jpg>

I'm not sure yet how to interpret the difference between
o acceleration
o linear acceleration
Given what I want is
o lateral acceleration
<https://i.postimg.cc/qqZJjcfZ/accelerate02.jpg>

[Xeno]

On 22/6/19 4:56 am, Arlen G. Holder wrote:
> On Fri, 21 Jun 2019 01:11:25 +1000, Xeno wrote:
>
>> No but, as stated, that particular feathered tread effect was pretty
>> unequivocal as to its cause.
>
> I thank you, Xeno (and Clare) for UNDERSTANDING my particular issue.
>
> I'm not actively participating simply because I'm embarrassed that I can't
> add any additional value, in that I can _read_ what Xeno (and Clare) say,
> and I can understand what they say, but when I've been driving the road
> daily (multiple times), I keep trying to _imagine_ what is happening, while
> I'm taking those turns with steering wheel inputs of
> o Mostly 90 degrees each way (some less, some more)
> o Some almost 360 steering wheel inputs
> o Some even 90 degrees more than 360 degree steering inputs
> All at around 20, to 30, to 40 (but no higher) speeds.

Just turn your wheels to the full lock whilst parked on a flat surface.
Then get out and look at the steering angles, in particular the camber
on the front inside wheel. Then imagine what is happening at the tread
blocks at that inside wheel noting that they do not follow a straight
path when driving with the wheel at that steer angle, camber and lateral
acceleration.
BTW, page 348 of the above linked book depicts the type of tyre
deformation I am on about. It applies to zero camber events however. Try
to imagine what it will look like if the tyre is up on one (outer) edge
and pressing hard on the tread shoulder.

>
> I did air up the tires, in an attempt to keep the tread more "firm", where
> I will check front camber & caster separately (I need the tools first).
>
> I picked up what seems to be a great free accelerometer graphical tool
> o Sensors Multitool, version 1.3.2, by Wered Software
> <https://play.google.com/store/apps/details?id=com.wered.sensorsmultitool>
>
> Here's a screenshot of the output on my Android device but I need to test
> it further before making any "lateral acceleration" claims ... where I'm
> not sure exactly yet how to test other than to put the phone on the seat as
> I drive downhill (uphill seems to have lesser forces for some reason).
> <https://i.postimg.cc/7hPhBY5b/accelerate01.jpg>
>
> I'm not sure yet how to interpret the difference between
> o acceleration
> o linear acceleration
> Given what I want is
> o lateral acceleration
> <https://i.postimg.cc/qqZJjcfZ/accelerate02.jpg>
>

[Xeno]

On 22/6/19 8:57 am, Xeno wrote:
> On 22/6/19 4:56 am, Arlen G. Holder wrote:
>> On Fri, 21 Jun 2019 01:11:25 +1000, Xeno wrote:
>>
>>> No but, as stated, that particular feathered tread effect was pretty
>>> unequivocal as to its cause.
>>
>> I thank you, Xeno (and Clare) for UNDERSTANDING my particular issue.
>>
>> I'm not actively participating simply because I'm embarrassed that I
>> can't
>> add any additional value, in that I can _read_ what Xeno (and Clare) say,
>> and I can understand what they say, but when I've been driving the road
>> daily (multiple times), I keep trying to _imagine_ what is happening,
>> while
>> I'm taking those turns with steering wheel inputs of
>> o Mostly 90 degrees each way (some less, some more)
>> o Some almost 360 steering wheel inputs
>> o Some even 90 degrees more than 360 degree steering inputs
>> All at around 20, to 30, to 40 (but no higher) speeds.

This link, forgot to put it in.

https://www.academia.edu/people/search?utf8=✓&q=fundamentals+of+vehicle+dynamics

Thomas D. Gillespie-Fundamentals of Vehicle Dynamics -Society of
Automotive Engineers Inc (1992)

[Arlen G. Holder]

On Sat, 22 Jun 2019 08:57:48 +1000, Xeno wrote:

> Then get out and look at the steering angles, in particular the camber
> on the front inside wheel.

Hi Xeno,
As you know, the camber changes dramatically...
<https://www.quora.com/When-turning-I-see-there-is-a-plus-camber-in-a-vehicle-Why>

Here's a picture showing the camber change as the front wheel turns:
<https://d2o7bfz2il9cb7.cloudfront.net/main-qimg-f3f08a594ce66d2764746c1645771ce8>

Here's another:
<https://cdntdreditorials.azureedge.net/cache/8/d/9/0/f/5/8d90f5b90f991eb8aefd66b1e837ac0737a001bb.jpg>

And another...
<http://4.bp.blogspot.com/-rnM1KmWXFRs/VWr0hkBzz0I/AAAAAAAAHKU/hLjnGsxGgTc/s320/Camber%2Bcar.png>

> Then imagine what is happening at the tread
> blocks at that inside wheel noting that they do not follow a straight
> path when driving with the wheel at that steer angle, camber and lateral
> acceleration.

Yeah. Those two diagrams are rather enlightening, since, as you know, this
specific slow speed lock-to-lock tight turn issue isn't well described.
<https://i.postimg.cc/zG0PQ9GL/accelerate04.jpg>

It's good to see these diagrams we both spoke of in the last post:
<https://i.postimg.cc/YqBVL6PS/accelerate03.jpg>

> BTW, page 348 of the above linked book depicts the type of tyre
> deformation I am on about. It applies to zero camber events however. Try
> to imagine what it will look like if the tyre is up on one (outer) edge
> and pressing hard on the tread shoulder.

I saw that contact patch deformation section about the slip region...
<https://i.postimg.cc/RFQ1d7DL/accelerate06.jpg>
where almost every sentence in that book takes a few re-takes since it's so
detailed, mathematically, where I'm trying to understand better, as you're
aware, the slow speed lock-to-lock cornering wear on front tires' outside
edge (one-way feathering).

For example, on page 342 are some nice diagrams, such as this:
<https://i.postimg.cc/Bv4dNghm/accelerate05.jpg>
Where they say:
"As the tread elements first enter the contact patch, they cannot develop
a friction force because of their compliance - they must bend to sustain a
force. This can happen only if the tire is moving faster than the
circumference of the thread".

Each sentence takes multiple passes to digest it more fully!

I'm still not exactly sure what's the easiest free way to measure lateral
acceleration with the Android smartphone yet though...

[Arlen G. Holder]

On Sat, 22 Jun 2019 08:59:29 +1000, Xeno wrote:

> This link, forgot to put it in.
> https://www.academia.edu/people/search?utf8=✓&q=fundamentals+of+vehicle+dynamics

Hi Xeno,
I much appreciate that you UNDERSTAND the complex geometric changes that
occur during camber scrub low-speed lock-to-lock conditions, where we both
agree the specific phenomenon I am troubleshooting is a specific very
mountainous situation which isn't covered well on the net, but which does
have pragmatic workarounds, as you & Clave have discussed.

Here's a shot from today with the vehicle parked at one of the curves.
o Passenger tire at (static) steering-wheel lock, heading uphill:
<https://i.postimg.cc/T1HkcsX5/mount31.jpg>
o Driver side tire at that same wheel lock situation:
<https://i.postimg.cc/KYXHVC3n/mount32.jpg>

It's not easy to tell, but that inner tire (which is the one wearing the
most in these slow speed lock-to-lock turns) should be taking on a more
positive camber, while the outer tire should be taking on a more negative
camber.

Even though the outside tire is taking on more of the force, the wear is
happening more so to the outside shoulder of the inside tire (the tire with
the more positive camber). <https://i.postimg.cc/YqHVb5gY/mount33.jpg>

As you've explained it prior, at _slow_ speeds (30 mph nominally), there
isn't as much weight transfer to the outside wheel, and yet the inside
wheel is at a tighter lock than the outside wheel due to Ackerman Angle
effects, where the more positive camber on that inside wheel causes the
outside tread area to longitudinally feather unidirectionally more so than
the outside wheel, which takes on a lesser more positive camber.

Since we're effectively riding on the outside tread blocks of the inside
tire, those outside blocks are forced to break traction and slide, which is
what's causing the longitudinal unidirectional feathering, particularly
when traveling downhill.

Note that the passenger tire of this rather heavy bimmer SUV is the
original tire of only about a year and a half old (about 15K miles or so),
where the outside edge counter rotational longitudinal feathering is almost
worn away, but the driver's side tire had to be replaced a few months ago,
where the counter rotational longitudinal feathering is easily felt on the
outside few inches of the tread.

Am I correct that these are the possible ameliorations, bearing in mind
that every change made has an effect somewhere else in alignment and that
each change has to be made in the standard caster/camber/toe order?
1. First, increase tire pressure (to decrease tread squirm)
2. Second, potentially decrease positive caster (to the low end of spec)
(where the goal is to change how SAI affects the camber angle under turns)
3. Third, possibly (increase?) static negative camber (within spec)
(although increasing negative static camber "may" also decrease the SAI)
4. Set toe to spec last.
[If I got anything wrong, please let me know as it's confusing!]

Obviously this is a compromise, as weight shift, self centering and
steering forces may correspondingly change at speed, as you're well aware
from this video clip you prior suggested
<https://youtu.be/VbReLNi2JP4?t=831>

[Arlen G. Holder]

On Sat, 22 Jun 2019 08:17:00 -0000 (UTC), Arlen G. Holder wrote:

> As you know, the camber changes dramatically...
> <https://www.quora.com/When-turning-I-see-there-is-a-plus-camber-in-a-vehicle-Why>

The one thing I can't wrap my head around is that they say the positive
camber on inside tires when cornering turns into a NEGATIVE camber if just
the force vectors are considered.
<https://i.postimg.cc/YqHVb5gY/mount33.jpg>

What the heck does that mean?
I don't get it...