Maximum Tire pressure (a police perspective)
Built_Well
We've talked here before about max cold tire inflation pressure.
Here's a fascinating article from Officer.com . Some police
officers drive with maximum air pressure in their tires as shown
on the tire sidewall, not the door sill or the owner's manual.
Here's a link to the article for some great photographs:
http://www.officer.com/article/article.jsp?siteSection=19&id=27281
and here's the text in case the page is deleted in the future:
Driving Under Pressure
Proper Tire Pressure Could Save Your Life
Posted: Wednesday, December 21, 2005
SGT. DAVE STORTON
EVOC Contributor
Officer.com
How many officers check the tire pressure on their patrol car
on a regular basis? We all seem to be great at checking that
the lights and siren work, because the time to find out they
don't work is not when you get a Code 3 call. Likewise, the
time to find out your tire pressure is too low is not when you
are in a pursuit and trying to take a corner at high speed.
What is proper pressure?
The proper tire pressure for the Police Crown Victoria is 44 psi.
If you look on the sidewall of the tire, you will see that it
lists 44 psi max pressure. Regardless of what vehicle you have,
use the maximum pressure listed on the sidewall. Higher pressure
results in better performance, decreased tire wear, and it
lessens your chance of hydroplaning at a given speed. This number
on the sidewall lists the maximum amount of pressure you should
ever put in the tire under normal driving conditions. Pursuits
and Code 3 responses are not normal driving conditions. Many
agencies maintain tire pressure at 35 psi since this is what
is listed in the owner's manual and on the door placard. The
reason the owner's manual lists 35 psi is because we get the
same manual as the civilian version of the Crown Victoria. The
police version, however, is fully loaded with communications
equipment, a cage, and your gear. You are not looking for a soft
and cushy ride, you want performance.
Myths about pressure
Let's put to rest some common misconceptions. The tires will
not balloon out creating a peak in the center portion of the
tread when tire pressure is above 35 psi. There is a steel belt
that prevents this from happening. Also, you are not
overstressing the tire with higher pressure, and the tire will
not be forced off the rim with higher pressure. The picture
above is Bobby Ore of Bobby Ore Motorsports driving a Ford Ranger
on two wheels. The tires on the left side have 100 psi in them,
and they happen to be tires and rims from a 1999 Crown Victoria!
This is a dramatic example of how pressure holds the tire in
shape, and how much stress a tire can handle.
Performance
If you were able to watch a tire as it travels across the
ground at high speed, you would see that it deflects to one
side during cornering. The faster you are going through a corner,
the more tire deflection you get. As the tire deflects over onto
the sidewall, you get less traction and more of a tendency to
understeer or oversteer. This could spell disaster when
negotiating a corner at high speed during a pursuit or a Code 3
run. Higher pressure keeps the tire from deflecting onto the
sidewall as much, which keeps more of the treaded portion on
the road.
A good demonstration for EVOC instructors is to have students
drive a high-speed course in a vehicle with 32 to 35 psi. Then
have them run the same course with 44 to 50 psi in the tires.
The student will experience a marked difference in performance.
Having officers experience this difference in vehicle
performance is much more effective than just telling them to
check their tire pressure.
Hydroplaning
When a tire rolls across a road covered with water, the tire
tread channels water away so the rubber remains in contact with
the road. The factors that affect hydroplaning are speed, and
water depth. Conventional wisdom says that vehicles will hydroplane
in as little as 1/16th of an inch of water. Not so coincidentally,
legal tread depth is 1/16th of an inch.
Tire manufactures and the Association of Law Enforcement Emergency
Response Trainers International (ALERT) have shown that tires have
more of a tendency to hydroplane when pressure is low. This
happens because the tire footprint (the portion of the tire
actually in contact with the road) is larger. For those of you
who water ski, think of which is easier to get up on: a fat ski
or a skinny ski. More tire surface in contact with the water
makes it easier to hydroplane, just as it is easier to water ski
on a fat ski. Also, a soft tire can be pushed in more by the
pressure of the water on the center portion of the tread. This
results in less rubber in contact with the road.
Tire wear
Much better tire wear results from maintaining proper pressure.
Tires with lower pressure will wear off the outside of the tread
faster from the deflection of the tire during cornering, and the
tires will heat up more from increased road friction. This is one
of the factors that caused the failure of a certain brand of
tires on Ford Explorers some years ago. In 1999 the San Jose
Police Department realized a significant cost savings by
increasing the pressure in the training fleet to 50 psi. They
soon followed up by increasing the pressure in the patrol fleet
to 44 psi. For liability reasons, most agencies are reluctant to
exceed the maximum pressure listed on the tire for actual patrol
vehicles, but they reap the cost saving when going to 50 psi on
training vehicles.
Next time you inspect your vehicle, make sure you check your
tire pressure since your ability to performance drive is
significantly affected by it. You are not driving to the store
to get a loaf of bread! You may be called upon to chase a
dangerous criminal or respond to assist another officer in
trouble. You don't wonder whether or not your gun is loaded
before you hit the street; don't wonder whether your tire
pressure is correct once the pursuit starts. Check your tires
routinely, just as you do with all other critical equipment.
--
Sgt. Dave Storton is the Director of the San Jose Police
Academy, and he holds a Master's Degree in Adult Education.
He is the lead instructor for the Emergency Vehicle Operations
Course (EVOC) at the San Jose Police Academy, and is a lead
instructor for the local regional academy. He teaches EVOC
instructor courses, advanced EVOC instructor courses, off road
EVOC, counter-terrorist / dignitary protection driving, and
motion picture stunt driving. Dave has trained over 3,500
drivers.
Photo courtesy of Bobby Ore Motorsports
ransley
Well wait, I blew a belt in a new Michelin going to max pressure, max
pressure gives less rubber on road that is less safe in stopping. and
isnt Max pressure the Max, not cold, hot it can increase 3-4lb
Mike Romain
I can only say this. When I put my 33x9.5" BFG 'mud terrain' tires up
to the max on the sidewall, or 50 psi, the amount of tread 'touching'
the ground is a strip 3" wide in the middle. This is determined by
covering the tread in chalk and driving forward straight.
It will then do 360's faster than you can blink in the rain hard like
that....
The measured total width of my tread is 7.5".
When I then go to 'proper' pressure or 30 psi, I then have 7" of my
tread touching the ground.
I do not drive at high speed, nor do I take corners like a cop though...
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
'New' frame in the works for '08. Some Canadian Bush Trip and Build
Photos: http://mikeromainjeeptrips.shutterfly.com
Built_Well wrote:
<SNIP>
N8N
> We've talked here before about max cold tire inflation pressure.
> Here's a fascinating article from Officer.com . Some police
> officers drive with maximum air pressure in their tires as shown
> on the tire sidewall, not the door sill or the owner's manual.
>
> Here's a link to the article for some great photographs:
>
> http://www.officer.com/article/article.jsp?siteSection=19&id=27281
<snip>
That info may be correct for a CV as it is a fairly heavy vehicle, but
it's entirely possible that a smaller, lighter vehicle would respond
better to *lower* tire pressure. In fact, the article contradicts
itself:
> Tire manufactures and the Association of Law Enforcement Emergency
> Response Trainers International (ALERT) have shown that tires have
> more of a tendency to hydroplane when pressure is low. This
> happens because the tire footprint (the portion of the tire
> actually in contact with the road) is larger. For those of you
> who water ski, think of which is easier to get up on: a fat ski
> or a skinny ski. More tire surface in contact with the water
> makes it easier to hydroplane, just as it is easier to water ski
> on a fat ski. Also, a soft tire can be pushed in more by the
> pressure of the water on the center portion of the tread. This
> results in less rubber in contact with the road.
doesn't "less rubber in contact with the road" imply reduced dry
weather performance?
As always, I'd take the advice given with a grain of salt. The
conclusions reached may be valid *for the specific vehicles under
discussion* but certainly can't be extrapolated to the vehicular
population as a whole.
nate
ransley
Another thing, it will prematurly wear out in the center, besides not
being as safe in handling.
BobJ
I purchased an M35 a year and a half ago. Surprisingly
Infiniti, in their "infinite" wisdom decided to install
Goodyear RSA tires on these cars. These tires have been
blasted left and right by every owner I've spoken with.
They're pure crap. During the first month of ownership, on
one occassion, I had to drive from Florida to the Washington
area, at 55 to avoid vibration. The problem was taken
care of by the dealer and I haven't had any issues since,
but here's the kicker...
The door jamb says to use 33psi cold......the owners
manual says to use 35psi cold. The tires say max pressure
of 40..... I've used 38 as a norm and the tire wear is
pretty even..
Since it's a regular practice for dealer to use a low air
pressure setting in the tires to give a soft ride, I can't
believe anything except what I find good for me.. The one
problem with these w i d e low profile tires is that any
change in temperature, especially around the change of
seasons, can significantly change your tire pressure, to
the tune of up to 5psi. Along with safety issues and the
price of 18" tires, it would be very rewarding for you to
pay attention to the tire pressures.
ray
tire pressure is some kind of black art.
I can see a cop car wanting max pressure, because they are often driven
fully loaded...
Here's my real world experiences:
2001 TA. Manual says 30psi. Unless you're normally driving above
100mph, and then you need to run 38psi. I love that part of the manual. :)
1990 1/2 ton. "Big" 265/75R16 all seasons. "Normal" is 45psi. Pump
'em up to 65 for towing one time, and the truck rides better. Even empty.
When I was autoXing, we'd pump up the tires to 35-40 to keep the tire
from folding over.
Drag racing - my drag radials run around 18-20 pounds.
Dirt racing - the guys with bias ply's run like 12 pounds, I run radials
and the best grip is around 18-20 pounds cold. the RF goes up to 35-38
by the end of 200 laps.
Ray
*
ransley <Mark_R...@yahoo.com> wrote in article
<165cba1e-d46b-4ec3...@2g2000hsn.googlegroups.com>...
Another thing, it will prematurly wear out in the center, besides not
being as safe in handling.
----------
Actually, an over-inflated, steel-belted tire will wear the outer edges of
the tire - just as though it was under-inflated.
The belt holds the center of the tread in position while the pressure
stretches the outer portion of the tread around the edges of the belt.
John Kunkel
"Built_Well" <Built_We...@hotmail.com> wrote in message
news:789ef876-0cdb-4156...@m45g2000hsb.googlegroups.com...
>
> We've talked here before about max cold tire inflation pressure.
> Here's a fascinating article from Officer.com . Some police
> officers drive with maximum air pressure in their tires as shown
> on the tire sidewall, not the door sill or the owner's manual.
>
> Here's a link to the article for some great photographs:
>
> http://www.officer.com/article/article.jsp?siteSection=19&id=27281
>
More reading:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=38&GCID=C13674x032&code=yes
Mike
"*" <nos...@this.addy.com> wrote in message
news:01c8c0d0$952946e0$6490c3d8@race...
Bullshit. Over-inflate any tire and it will wear the center first.
*
Mike <m...@localnet.com> wrote in article
<zak%j.5176$%z4....@fe119.usenetserver.com>...
So, you're saying that the steel belt will stretch before the rubber and
fabric tread edges???
THAT's logical?!?!?
I've seen it happen.
Mike Romain
It has zip to do with the steel belt. Proper inflation has a tire with
a flat bottom, overinflate it 'for the weight of the vehicle' and the
tire goes round. The vehicle can no longer hold the 'flat' of the tire
down.
We are not talking putting 100 psi in it, only 'up to' the max on the
sidewall!
That 'for sure' is what happens on my current BF Goodrich tires and
every other tire I have ever played with the inflation levels on.
As I mentioned, put 50 psi in my tires (the sidewall max) and only a 3"
width of tread touches the ground, go to the proper 30 and 7 out of 7.5"
touches the ground.
The folks that off road and run oversized tires, have to have a way to
see if their pressure is correct so we use the 'chalk' method. We cover
the tread with chalk lines and drive forward to see how much 'rubber' is
touching the ground. We then adjust our tire pressures accordingly.
Mike
Bullshit ! I have used steel belted radials since they came out and have
NEVER seen this happen. If you over-inflate the tires they wear in the center,
under-inflated they wear on the edges. The steel belts are not solid steel,
they are a woven steel mesh and are able to stretch and flex with the rubber
in the tire. I have seen customers come in complaining of a harsh ride and the
tire pressures have been in the 90 - 120 PSI range and the tread was worn off
in the center of the tire, never on the edges. Your misleading information may
cost someone their life if they are dumb enough to believe you!
ransley
> ransley <Mark_Rans...@yahoo.com> wrote in article
> <165cba1e-d46b-4ec3-a9b9-c139d5d0d...@2g2000hsn.googlegroups.com>...
>
> Another thing, it will prematurly wear out in the center, besides not
> being as safe in handling.
>
> ----------
>
> Actually, an over-inflated, steel-belted tire will wear the outer edges of
> the tire - just as though it was under-inflated.
>
> The belt holds the center of the tread in position while the pressure
> stretches the outer portion of the tread around the edges of the belt.
Oh BS, prove it to your dumb ass self, Get water on your driveway,
drive throught it and measure the tread width, go pump up your tires
20 lb and do it again, you will have less tread on the ground with
more pressure, what touches is what wears.
John S.
Aside from riding like an empty lumber truck, wearing out the tire
center prematurely, risking a blowout and giving imprecise and jittery
handling I see no problem at all running at the maximum sidewall
pressure. Gawd what misinformation.
*
Mike <m...@localnet.com> wrote in article
<2cz%j.303$Cr....@fe101.usenetserver.com>...
Well, tire dyno tests at places such as Calspan have proven what I say to
be true.
Over-inflation places more pressure on the outer edges due to the tire
bulging out over the belt.
I'll bet the over-inflated radials you talk about that wore in the center
were mounted on the rear wheels.
Even properly inflated radials tend to wear on the edges in front, and the
centers in back (on a RWD, of course.)
How does what I say endanger ANYBODY. I am not endorsing either over- or
under-inflation.
Daniel
Gawd what misinformation.
========
Consider the source.
I've seen Highway Patrol Crown Victorias zooming by at well over 100
mph on the freeways, plus they mention extra weight of special
equipment. Not uncommon to add pressure for high speed use and extra
weight. An extra 5 psi for speeds over 100 mph would bring 35 to 40,
so they're only adding another 4 psi for additional weight and firmer
handling for the police vehicle. The advice to check pressure
regularly is good.
The mistake is posting to the Camry group.
From 35 psi to 44 in a Police Crown Vic is quite different from
running 44 psi in the rear tires of a Camry. Roughly 3,000 lbs., split
60/40, F/R, puts only 600 lbs. load on a rear tire, so the tires would
be dangerously overinflated in the one case but could be fine in the
other specialized use.
Factory inflation on the Generation 3 Camry, 4 cyl. is 26 psi. 28/26.
F/R unladen seems best overall. Factory says 29 F/R for 4 passengers
with luggage. (Those used the 14 inch 70 series tires). Because the
tires carry maximum load of 1312 lbs. at 44 psi, doesn't mean one
should use that cold inflation pressure to carry less than half that
standard load.
Mike
Got a link to that article ?
>
> Over-inflation places more pressure on the outer edges due to the tire
> bulging out over the belt.
>
> I'll bet the over-inflated radials you talk about that wore in the center
> were mounted on the rear wheels.
Nope. Front wheels.
>
> Even properly inflated radials tend to wear on the edges in front, and the
> centers in back (on a RWD, of course.)
What's your definition of porperly inflated ? If the tires were properly
inflated they would wear evenly regarless of which axle they are installed on.
Wear on the front edges is not due to steel belted radial design, it has more
to due with front end geometry and tire design. Front whell drive and four
wheel drive vehicles seem to have more of a problem with this.
>
> How does what I say endanger ANYBODY. I am not endorsing either over- or
> under-inflation.
The person who's tires are already under-inflated that believes the steel
belt tale and lets more air out to get even tread wear. Remember the
Ford/Firestone fiasco ?
ChrisCoaster
> "*" <nos...@this.addy.com> wrote in message
>
> news:01c8c26a$af188200$5295c3d8@race...
>
>
>
>
>
>
>
> > Mike <m...@localnet.com> wrote in article
> > <2cz%j.303$Cr....@fe101.usenetserver.com>...
>
> >> "*" <nos...@this.addy.com> wrote in message
> >>news:01c8c17f$614b6ec0$2795c3d8@race...
>
> >> > Mike <m...@localnet.com> wrote in article
>
> - Show quoted text -
_____________
You know, The WAR IN IRAQ is a less contentious debate than cold tire
pressure!
That's 'effin SAD, if you want my honest opinion.
GM, Ford, Toyota, Chrysler, BMW, and all the others do a lot of test
driving of their vehicles to come up with the recommended pressures
they list on the door pillar or under the trunk lid. And in some
cases, as was with my 1981 Buick Century of which I owned two during
my college years, the recommended pressure DOES = the maximum allowed
pressure on the tire sidewall.
But in the cases where the auto mfg's recommended pressure is, say, 30
F/R or 32F / 34R, then I would think someone is pretty 'effin STUPID
to put 45lbs. psi of air in them just because "that's what the TIRE
says"!
I like to WATCH basketball, NOT feel like I'm driving one or a
passenger in one - thank you very effin' much!
-Chris-"1lb psi cold above door-jamb sticker" - Coaster
ray
>
> As I mentioned, put 50 psi in my tires (the sidewall max) and only a 3"
> width of tread touches the ground, go to the proper 30 and 7 out of 7.5"
> touches the ground.
>
What about wide low profile tires? Would it be as extreme? I'm curious
- my Trans Am comes out of storage tomorrow and it has 275-40/17's, so
now I'm going to see if I can actually see if it looks "bulged" with max
pressure in it. Then I'll do a couple of burnouts for science to see
what the contact patch looks like. Then I'll bleed some air out and do
some more burnouts. Then I'll just drive around for a couple of hours
and do burnouts. Yeah, I'm a goof, but I love burnouts. I don't know
why, but I do. If I ever re-do my driveway, I'm getting a concrete
launch pad installed because I actually tore up the asphalt with my
truck doing... a burnout to test the posi. :)
Ray
Scott Dorsey
Put some chalk on the tires and drive around the block. You'll see pretty
well what is going on.
I find that the optimal contact with the tires on my car is a little bit
more than the owner's manual says is appropriate with OEM tires, and a good
bit less than what the maximum allowed by the tires is.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Mike Romain
LOL! Well, I only got 2.75" touching when I spun them up hard, a bit
less than the chalk test gave me. I had to test my new clutch out eh.
Mike
*
Mike <nos...@nospam.com> wrote in article
<xTZ%j.62$oA...@fe105.usenetserver.com>...
>
>
> What's your definition of porperly inflated ? If the tires were properly
> inflated they would wear evenly regarless of which axle they are
installed on.
> Wear on the front edges is not due to steel belted radial design, it has
more
> to due with front end geometry and tire design. Front whell drive and
four
> wheel drive vehicles seem to have more of a problem with this.
>
>
Now, your ignorance is showing......the term "ignorance" meaning something
you are not aware of, and not meant as a personal insult.
Anybody who works on cars professionally and removes tires on a regular
basis will tell you that drive tires wear in the center - mostly due to the
belt "pulling" the tread on acceleration and deceleration inputs - and
steering tires wear on the edges - even with absolutely correctly aligned
wheels. On RWD cars, this results in the rear tires wearing in the center
and the fronts wearing equally on both edges - even when properly inflated.
On FWD cars with both steering and drive inputs on the front tires, the
rears will often outlast two sets of front tires.
> > How does what I say endanger ANYBODY. I am not endorsing either over-
or
> > under-inflation.
>
>
> The person who's tires are already under-inflated that believes the
steel
> belt tale and lets more air out to get even tread wear. Remember the
> Ford/Firestone fiasco ?
>
>
>
OTOH, if the edges wear on an overinflated tire and the person believes
YOUR THEORY that edge wear automatically indicates underinflation, they
could overinflate the tire and have it pop on a hot summer's day at 70+ mph
on the Interstate.
Anybody who sets tire pressures by the tire's appearance is too stupid to
be operating a machine as complex as an automobile.
*
ransley <Mark_R...@yahoo.com> wrote in article
<c261d6b0-8b59-44cb...@d77g2000hsb.googlegroups.com>...
----------
Check out the various papers devoted to tire over/under inflation at
www.sae.org.
That's the Society of Automotive Engineers, dumbass!
I suppose your "water test" is a bit more sophisticated that their tests,
eh?
*
ransley <Mark_R...@yahoo.com> wrote in article
<c261d6b0-8b59-44cb...@d77g2000hsb.googlegroups.com>...
Oh BS, prove it to your dumb ass self, Get water on your driveway,
drive throught it and measure the tread width, go pump up your tires
20 lb and do it again, you will have less tread on the ground with
more pressure, what touches is what wears.
----------
If the ONLY application for the tire was to be rolling across the wet
driveway at <5 mph, you would be in pretty good shape there, Studley!
You are not accounting for a myriad of forces that affect the tire as
speeds increase - one of which would be cenrifugal forces applied to the
tread.
I would prefer to ( and I do! ) run the tire up to temperature at speed,
then measure temperatures across the tread with a pyrometer to get an idea
of what is happening in the real world - you know, like tire engineers do
at places such as Indy and Daytona, and their own tire test tracks?
I know that tire temperature is one factor used in coming up with the
recommended pressures that are posted at the back of the tire truck at each
race.
And, yes! An overinflated, steel-belted radial used in a lower division
"stock tire" racing class WILL show warmer temperatures on the outer edges
of the tread.
Before this was realized, race team tire people couldn't understand how
adding pressure didn't fix the "apparent underinflation" exhibited by
elevated outer tread surface tire temperatures.
John S.
Pressure is pressure no matter the car. The Crown Vic has much larger
tires to compensate for the much larger car, but 45 psi is still too
hard for safety.
Mike
>
>
> ransley <Mark_R...@yahoo.com> wrote in article
> <c261d6b0-8b59-44cb...@d77g2000hsb.googlegroups.com>...
>
>
> Oh BS, prove it to your dumb ass self, Get water on your driveway,
> drive throught it and measure the tread width, go pump up your tires
> 20 lb and do it again, you will have less tread on the ground with
> more pressure, what touches is what wears.
>
> ----------
>
> If the ONLY application for the tire was to be rolling across the wet
> driveway at <5 mph, you would be in pretty good shape there, Studley!
>
> You are not accounting for a myriad of forces that affect the tire as
> speeds increase - one of which would be cenrifugal forces applied to the
> tread.
>
> I would prefer to ( and I do! ) run the tire up to temperature at speed,
> then measure temperatures across the tread with a pyrometer to get an idea
> of what is happening in the real world - you know, like tire engineers do
> at places such as Indy and Daytona, and their own tire test tracks?
You do this on your daily driver ?
>
> I know that tire temperature is one factor used in coming up with the
> recommended pressures that are posted at the back of the tire truck at each
> race.
>
> And, yes! An overinflated, steel-belted radial used in a lower division
> "stock tire" racing class WILL show warmer temperatures on the outer edges
> of the tread.
Ah, I now see were the problem is ! You are talking about race car tire
wear and we are talking about street car tire wear. Of coarse hard cornering
will heat up the outer edges of a tire. This will happen on a race car AND
street driven vehicles. I like to corner hard and always have edge wear on my
front tires even if I up the inflation by a few psi.
Mike
>
>
> Mike <nos...@nospam.com> wrote in article
> <xTZ%j.62$oA...@fe105.usenetserver.com>...
>>
>>
>> What's your definition of porperly inflated ? If the tires were properly
>
>> inflated they would wear evenly regarless of which axle they are
> installed on.
>> Wear on the front edges is not due to steel belted radial design, it has
> more
>> to due with front end geometry and tire design. Front whell drive and
> four
>> wheel drive vehicles seem to have more of a problem with this.
>>
>>
>
>
> Now, your ignorance is showing......the term "ignorance" meaning something
> you are not aware of, and not meant as a personal insult.
>
> Anybody who works on cars professionally and removes tires on a regular
> basis will tell you that drive tires wear in the center - mostly due to the
> belt "pulling" the tread on acceleration and deceleration inputs
As someone who has worked on cars professionally for the last 25 years I have
to wonder were you get your information from. I have never seen a properly
inflated tire wear in the center, NEVER, drive tire or not ! Also, when I
say properly inflated I don't mean going by the door jamb sticker. The
manufacturer may set the recomended pressure a little low for a better ride
and this will cause the tires to wear on the edges. Inflate the tire to proper
pressure and the edge wear stops.
- and
> steering tires wear on the edges - even with absolutely correctly aligned
> wheels.
Not with properly inflated tires unless you like to corner fast.
On RWD cars, this results in the rear tires wearing in the center
> and the fronts wearing equally on both edges - even when properly inflated.
Bullshit ! A properly inflated tire WILL NOT wear in the center! I have
seen thousands of tires on all kinds of vehicles and the ONLY cause of
centere tread wear in OVERINFLATION !
Front tire edge wear is common on some vehicles due to suspension geometry
but MOST vehicles will not show egde wear in normal driving unless the are
underinflated.
>
> On FWD cars with both steering and drive inputs on the front tires, the
> rears will often outlast two sets of front tires.
Thar's why you rotate your tire on a regular basis.
>
>> > How does what I say endanger ANYBODY. I am not endorsing either over-
> or
>> > under-inflation.
>>
>>
>> The person who's tires are already under-inflated that believes the
> steel
>> belt tale and lets more air out to get even tread wear. Remember the
>> Ford/Firestone fiasco ?
>>
>>
>>
>
>
> OTOH, if the edges wear on an overinflated tire and the person believes
> YOUR THEORY that edge wear automatically indicates underinflation, they
> could overinflate the tire and have it pop on a hot summer's day at 70+ mph
> on the Interstate.
Wrong again. If you read the vehicle owners manual or the tire
manufacturers websites you will notice that for sustained high speed driving
they recommend you INCREASE the tire pressure. LOW tire pressure causes the
tire to flex, which causes heat buildup and can soften the tire and cause it
to fail. An overinflated tire will wear in the center but WILL NOT blow out.
+
>
> Anybody who sets tire pressures by the tire's appearance is too stupid to
> be operating a machine as complex as an automobile.
>
Not sure what you mean by "appearance" ? If you mean looking at the
sidewall to visually determine if the tire is properly inflated then I agree.
If you mean by looking at tread wear then I don't agree, and neither do the
tire manufacturers. Got to any tire manufacturers website and most will have
pictures that show uneven wear on tires due to improper inflation.
*
Mike <nos...@nospam.com> wrote in article
<zgA0k.1601$4l5...@fe103.usenetserver.com>...
Then that blows your theory about overinflation/center-tread wear. You
SHOULD be able to add enough air to compensate for your driving style, and
give you even tread wear by making the centre of the tread work harder.
*
Mike <nos...@nospam.com> wrote in article
<ygA0k.1599$4l5...@fe103.usenetserver.com>...
But, if YOU are correct regarding overinflation/center tread wear, you
SHOULD be able to increase tire pressures to the point that the center
wears evenly with the edges.
> On RWD cars, this results in the rear tires wearing in the center
> > and the fronts wearing equally on both edges - even when properly
inflated.
>
>
> Bullshit ! A properly inflated tire WILL NOT wear in the center! I
have
> seen thousands of tires on all kinds of vehicles and the ONLY cause of
> centere tread wear in OVERINFLATION !
>
Apparently, you have not learned a lot in your 25 years of "professional"
work.....that, or you simply don't pay much attention to the vehicles you
work on.
dave...@aol.com
thekma...@gmail.com
I have personal eyewitness(or seat-witness) testimony of a friend who complained of "something wrong" with her car's ride or its alignment.
She said it was very hard to steer accurately and was very bouncy and shakey.
I checked her pressures after about one hour sitting in our driveway. One tire was 50, the others, 47-48psi. Max. cold placard on her tires states 51psi. Specified cold sticker on the driver's B-pillar: 30psi F&R.
I lowered all four to exactly 38psi(knowing that they would cool off by next morning and would go down). She said her car "never felt this good or was so easy to handle". The steering was taut and at same time responsive.
She returned in two days to conduct business with my wife - she sells cookware - and I checked her pressures after she'd been parked here a while. 35 all around. I left them there, but told her to tell her mechanic to put no more than 36pounds hot in those things!
Maximum cold tire placard does have some utility: Constant use with full load of passengers and/or cargo comes to mind, or towing vehicles/vessels. But for most solo driving, or with one/two passenger, max cold on the tire placard could translate to driving a basketball!
I keep my personal vehicle and my wife's at 'plus-two': 2psi over b-pillar door sticker. No complaints from either of us. :)
116...@gmail.com
as a cop Crown Vic.
I would never put more than 40 PSI in the tyres.
m6onz5a
thekma...@gmail.com
thekma...@gmail.com
Brian Gordon
specifies? Why?
--
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| Brian Gordon -->bri...@panix.com<-- brian dot gordon at cox dot net |
+ briang...@hotmail.com Bass: Lexington "Main Street Harmonizers" chorus +
-------------------------------------------------------------------------------
Bill Vanek
Gordon) wrote:
>In article <fd070c52-b135-40f3...@googlegroups.com>,
> <thekma...@gmail.com> wrote:
>>On Tuesday, June 17, 2014 9:17:03 AM UTC-4, 116...@gmail.com wrote:
>>> I have driven large RWD cars most of my life, although not quite as heavy
>>>
>>> as a cop Crown Vic.
>>>
>>> I would never put more than 40 PSI in the tyres.
>>
>>^ +1
>
>So on my SUV with 10-ply rear tires, I should ignore the 75PSI the manufacturer
>specifies? Why?
thekma...@gmail.com
75psi - tire placard or door post?
Brian Gordon
Scott Dorsey
>In article <acbbc9bc-feef-4c0a...@googlegroups.com>,
> <thekma...@gmail.com> wrote:
>>Brian Gordon:
>>
>>75psi - tire placard or door post?
>
>Door post and Owners' Manual
that you just hook up the pump, and you pump and pump until no more air will
go in and then it's correct.
He died of old age a decade ago, surprisingly. I was expecting him to die
in some horrible highway accident involving exploded tires...
Kevin Bottorff
news:1dd58cd4-7293-4dc6...@googlegroups.com:
but going over 40 lbs without a weight reason is probably not wise,
dollar wise. KB
dave...@aol.com
> We've talked here before about max cold tire inflation pressure.
> Here's a fascinating article from Officer.com . Some police
> officers drive with maximum air pressure in their tires as shown
> on the tire sidewall, not the door sill or the owner's manual.
>
> Here's a link to the article for some great photographs:
>
> http://www.officer.com/article/article.jsp?siteSection=19&id=27281
>
> and here's the text in case the page is deleted in the future:
>
> Driving Under Pressure
>
> Proper Tire Pressure Could Save Your Life
>
> Posted: Wednesday, December 21, 2005
>
> SGT. DAVE STORTON
> EVOC Contributor
>
> Officer.com
>
> How many officers check the tire pressure on their patrol car
> on a regular basis? We all seem to be great at checking that
> the lights and siren work, because the time to find out they
> don't work is not when you get a Code 3 call. Likewise, the
> time to find out your tire pressure is too low is not when you
> are in a pursuit and trying to take a corner at high speed.
>
> What is proper pressure?
>
> The proper tire pressure for the Police Crown Victoria is 44 psi.
> If you look on the sidewall of the tire, you will see that it
> lists 44 psi max pressure. Regardless of what vehicle you have,
> use the maximum pressure listed on the sidewall. Higher pressure
> results in better performance, decreased tire wear, and it
> lessens your chance of hydroplaning at a given speed. This number
> on the sidewall lists the maximum amount of pressure you should
> ever put in the tire under normal driving conditions. Pursuits
> and Code 3 responses are not normal driving conditions. Many
> agencies maintain tire pressure at 35 psi since this is what
> is listed in the owner's manual and on the door placard. The
> reason the owner's manual lists 35 psi is because we get the
> same manual as the civilian version of the Crown Victoria. The
> police version, however, is fully loaded with communications
> equipment, a cage, and your gear. You are not looking for a soft
> and cushy ride, you want performance.
>
> Myths about pressure
>
> Let's put to rest some common misconceptions. The tires will
> not balloon out creating a peak in the center portion of the
> tread when tire pressure is above 35 psi. There is a steel belt
> that prevents this from happening. Also, you are not
> overstressing the tire with higher pressure, and the tire will
> not be forced off the rim with higher pressure. The picture
> above is Bobby Ore of Bobby Ore Motorsports driving a Ford Ranger
> on two wheels. The tires on the left side have 100 psi in them,
> and they happen to be tires and rims from a 1999 Crown Victoria!
> This is a dramatic example of how pressure holds the tire in
> shape, and how much stress a tire can handle.
>
> Performance
>
> If you were able to watch a tire as it travels across the
> ground at high speed, you would see that it deflects to one
> side during cornering. The faster you are going through a corner,
> the more tire deflection you get. As the tire deflects over onto
> the sidewall, you get less traction and more of a tendency to
> understeer or oversteer. This could spell disaster when
> negotiating a corner at high speed during a pursuit or a Code 3
> run. Higher pressure keeps the tire from deflecting onto the
> sidewall as much, which keeps more of the treaded portion on
> the road.
>
> A good demonstration for EVOC instructors is to have students
> drive a high-speed course in a vehicle with 32 to 35 psi. Then
> have them run the same course with 44 to 50 psi in the tires.
> The student will experience a marked difference in performance.
> Having officers experience this difference in vehicle
> performance is much more effective than just telling them to
> check their tire pressure.
>
> Hydroplaning
>
> When a tire rolls across a road covered with water, the tire
> tread channels water away so the rubber remains in contact with
> the road. The factors that affect hydroplaning are speed, and
> water depth. Conventional wisdom says that vehicles will hydroplane
> in as little as 1/16th of an inch of water. Not so coincidentally,
> legal tread depth is 1/16th of an inch.
>
> Tire manufactures and the Association of Law Enforcement Emergency
> Response Trainers International (ALERT) have shown that tires have
> more of a tendency to hydroplane when pressure is low. This
> happens because the tire footprint (the portion of the tire
> actually in contact with the road) is larger. For those of you
> who water ski, think of which is easier to get up on: a fat ski
> or a skinny ski. More tire surface in contact with the water
> makes it easier to hydroplane, just as it is easier to water ski
> on a fat ski. Also, a soft tire can be pushed in more by the
> pressure of the water on the center portion of the tread. This
> results in less rubber in contact with the road.
>
> Tire wear
>
> Much better tire wear results from maintaining proper pressure.
> Tires with lower pressure will wear off the outside of the tread
> faster from the deflection of the tire during cornering, and the
> tires will heat up more from increased road friction. This is one
> of the factors that caused the failure of a certain brand of
> tires on Ford Explorers some years ago. In 1999 the San Jose
> Police Department realized a significant cost savings by
> increasing the pressure in the training fleet to 50 psi. They
> soon followed up by increasing the pressure in the patrol fleet
> to 44 psi. For liability reasons, most agencies are reluctant to
> exceed the maximum pressure listed on the tire for actual patrol
> vehicles, but they reap the cost saving when going to 50 psi on
> training vehicles.
>
> Next time you inspect your vehicle, make sure you check your
> tire pressure since your ability to performance drive is
> significantly affected by it. You are not driving to the store
> to get a loaf of bread! You may be called upon to chase a
> dangerous criminal or respond to assist another officer in
> trouble. You don't wonder whether or not your gun is loaded
> before you hit the street; don't wonder whether your tire
> pressure is correct once the pursuit starts. Check your tires
> routinely, just as you do with all other critical equipment.
> --
> Sgt. Dave Storton is the Director of the San Jose Police
> Academy, and he holds a Master's Degree in Adult Education.
> He is the lead instructor for the Emergency Vehicle Operations
> Course (EVOC) at the San Jose Police Academy, and is a lead
> instructor for the local regional academy. He teaches EVOC
> instructor courses, advanced EVOC instructor courses, off road
> EVOC, counter-terrorist / dignitary protection driving, and
> motion picture stunt driving. Dave has trained over 3,500
> drivers.
>
> Photo courtesy of Bobby Ore Motorsports
Thanks for re-posting my article. That was back from 2005. I have recently updated it to answer many of the questions and comments that article generated.
http://www.thedrivingcompany.com/driving-under-pressure.html
Ashton Crusher
looking at other reports it does seem that some vehicles and tires do
ok at pretty high tire pressures. While googling around I found this
http://www.performancesimulations.com/fact-or-fiction-tires-1.htm
which was a pretty interesting report on actual tire contact area
versus tire pressure. Results are nothing like expected.
Scott Dorsey
>
>I was surprised that the high pressure didn't cause problems but
>looking at other reports it does seem that some vehicles and tires do
>ok at pretty high tire pressures. While googling around I found this
>http://www.performancesimulations.com/fact-or-fiction-tires-1.htm
>which was a pretty interesting report on actual tire contact area
>versus tire pressure. Results are nothing like expected.
tires and drive around a bit.
Also notice that lateral stiffness will increase as you add air pressure,
and that may actually make more of a change in handling on some tires with
larger sidewalls than the change in contact area.
spiel...@gmail.com
I drive a police interceptor (Crown Vic) and also have Ford's installer's documents.
Although the tires may have either 35 or 44 psi on them, and although the civilian owner's manual and door sticker suggests 35 psi cold pressure, the police install documents suggest 41 psi as the correct cold psi for pursuit cars.
Every written article I have seen on optimal pressure for pursuit cars indicates 41 psi. This is also consistent with the tire manufacturer's indications for pressures at high speeds for V-rated tires.... the pressure goes up past the normal maximum rating of 35 as the top speed increases.
It seems most of these cars are run at 41 to 44 psi, with some agencies opting for 35, but few.
Tire wear and performance are better with these cars at higher psi.
thekma...@gmail.com
Over on rec.audio.pro, louder albums are better.
I operate nothing at max - always in the upper third of operating range. Sucks to be correct in a MAXED out world!