Shortening front forks.
Greg.Procter
returning to motorcycles after several decades of not motorcycling.
My present project is restoring an old motorscooter.
(make probably not relevant as it was a New Zealand product)
Step #2 is upgrading the motor so that I can keep up with modern traffic.
Step #3 has to be fitting modern disc brakes.
Step #4 then has to be upgrading the front suspension, which is where I
will run into big problems. The headstock is rigid enough and can be
further braced, but the forks are an inverted "Y" folded back slightly
with leading arms and short spring/damper units (parts bin engineering
from the manufacturer's motorcycle rear suspension)
My current thought is to make a more conventional motorcycle front end
with two triple plates only with much shorter sliding tube forks.
Has anyone got experience with front forks (say 250cc-350cc size) and
the possibilities of shortening them?
Regards,
Greg.P.
NZ
--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
The Older Gentleman
> Has anyone got experience with front forks (say 250cc-350cc size) and
> the possibilities of shortening them?
If you can find some forks that will fit the yokes, you don't have to
shorten them in order to make the motorcycle 'sit' correctly.
Just lift the forks through the yokes so you have an inch or two (or
whatever) protruding above the top yoke.
--
BMW K1100LT & K100RS Ducati 750SS Honda CB400F Triumph Street Triple
Suzuki TS250ER (currently Beaving) Damn, back to six bikes!
Try Googling before asking a damn silly question.
chateau dot murray at idnet dot com
M.Badger
> Hi all,
> returning to motorcycles after several decades of not motorcycling.
>
> My present project is restoring an old motorscooter.
> (make probably not relevant as it was a New Zealand product)
Intrigued now. Any chance of some pictures?
> Step #2 is upgrading the motor so that I can keep up with modern traffic.
Your wallet, but is it viable?
> Step #3 has to be fitting modern disc brakes.
A well setup drum brake, and very good forward planning ;-)
> Step #4 then has to be upgrading the front suspension, which is where I
> will run into big problems. The headstock is rigid enough and can be
> further braced, but the forks are an inverted "Y" folded back slightly
> with leading arms and short spring/damper units (parts bin engineering
> from the manufacturer's motorcycle rear suspension)
> My current thought is to make a more conventional motorcycle front end
> with two triple plates only with much shorter sliding tube forks.
> Has anyone got experience with front forks (say 250cc-350cc size) and
> the possibilities of shortening them?
Have a scout round a breakers and see if anything vaguely modern could be
adapted to fit. Once you have a stem/bearing set that fits, look very
carefully at the yoke offset needed from the stem.
>
> Regards,
> Greg.P.
> NZ
>
>
>
1949 Whizzer
> My present project is restoring an old motorscooter.
Step #1: SELL the old motorscooter to somebody who likes that
particular brand.
Those people are definitely OUT THERE, in more ways than one.
Step #2: Buy an old motorcycle that you can afford, preferably one
that was mass produced in Japan and imported by the millions into NZ.
Step #3: Fix it up, using aftermarket repair parts that you can easily
order from the interweb.
> My current thought is to make a more conventional motorcycle front end
> with two triple plates only with much shorter sliding tube forks.
Step #4: Next time you have such a creative thought, JUST LET IT GO.
> Has anyone got experience with front forks (say 250cc-350cc size) and
> the possibilities of shortening them?
Sure. You could install shorter stanchion tubes, shorter springs and
maybe even shorten the damper rods.
But it wouldn't be worth your time if you have the money to buy a real
motorcycle that does what you want.
And, if you don't have any money, the project will be just an exercise
in futility if some engine part or rear drive part gives you trouble.
Then you'd be back in here asking about motorcycle engines that you
could easily adapt to motor scooter style rear drive, or how to adapt
a motorcycle swing arm and a motorcycle engine to an old scooter.
Schiffner
Typical bad advice from a fake.
The Older Gentleman
> Sure. You could install shorter stanchion tubes, shorter springs and
> maybe even shorten the damper rods.
Or you could do what I suggest, which is raise them through the yokes.
As long as you don't mind maybe a couple of inches of stanchion poking
up.
1949 Whizzer
Argument, Neil Murray) wrote:
> Or you could do what I suggest, which is raise them through the yokes.
> As long as you don't mind maybe a couple of inches of stanchion poking
> up.
I don't feel like instructing Greg about the importance of matching
the front spring rate(s) to the rear spring rates and why that's
important to the overall ride comforts as well as traction balance.
And, if he found a set of forks for a more modern motorcycle which
used a 17-inch front wheel, he would still have a handling problem
because the rear wheel is probably a 12 or 14-incher.
The rider of a two wheeled vehicle with such a wheel/tire diameter
mismatch feels like the bike doesn't "want" to turn into a corner and
then it feels like the rear end is falling out from under him is the
turn.
The Older Gentleman
>
> And, if he found a set of forks for a more modern motorcycle which
> used a 17-inch front wheel,
Who said he would?
--
BMW K1100LT & K100RS Ducati 750SS Triumph Street Triple Honda CB400F
Suzuki TS250 chateaudotmurrayatidnetdotcom
Nothing damages a machine more than an ignoramus with a manual, a
can-do attitude and a set of cheap tools
Schiffner
Boy are you stupid. It's a motor-scooter NOT a 125cc street bike you
stupid git.
Schiffner
Gentleman) wrote:
> 1949 Whizzer <macmi...@gmail.com> wrote:
> > Sure. You could install shorter stanchion tubes, shorter springs and
> > maybe even shorten the damper rods.
>
> Or you could do what I suggest, which is raise them through the yokes.
> As long as you don't mind maybe a couple of inches of stanchion poking
> up.
uh, dude your senility is creeping in methinks...he's talking about a
motor-scooter.
paul c
Some scoots, such as a Honda CH250, could probably handle small bike
forks if the right sized races could be found, the fairing and inner
bodywork would probably have to go and then it would be a rat scoot.
The Older Gentleman
My bad for not reading the post properly. That said, grafting a
conventional front fork end on wouldn't be hard: just a waste of effort.
--
Greg.Procter
<totallyde...@yahoo.co.uk> wrote:
> Greg.Procter <pro...@ihug.co.nz> wrote:
>
>> Has anyone got experience with front forks (say 250cc-350cc size) and
>> the possibilities of shortening them?
>
> If you can find some forks that will fit the yokes, you don't have to
> shorten them in order to make the motorcycle 'sit' correctly.
>
> Just lift the forks through the yokes so you have an inch or two (or
> whatever) protruding above the top yoke.
>
Hi Older Gentleman,
the machine currently has an upside down "Y" made of welded tube - no
triple yokes and motorscooter superstructure around the head.
I'm a bit nervous of it's strength if I install better brakes and more
horsepower. The superstructure can be braced easily inside so I can keep
the external appearance.
Apologies for delay, my provider seems only to download about weekliy!
Greg.P.
Greg.Procter
> Greg.Procter wrote:
>
>> Hi all,
>> returning to motorcycles after several decades of not motorcycling.
>>
>> My present project is restoring an old motorscooter.
>> (make probably not relevant as it was a New Zealand product)
>
> Intrigued now. Any chance of some pictures?
Google "NZeta". Way back when New Zealand had strict fanancial rules
and most (90%) of our exports went to Britain. UK owed the US umpteen
times it's total worth so the UK pounds could only be spent back to
the UK or Commonwealth countries.
Motor vehicles had huge duties and sales tax but the duties were dropped
from NZ built vehicles. As we only had 2-3 million people the result was
a few types of vehicles partly manufactured here, based on existing brands,
eg Volkswagens; imported components 60%/NZ manufactured 40% - 40% of duty
knocked off.
Haven't bought it yet - have put in an auction bid though.
>
>> Step #2 is upgrading the motor so that I can keep up with modern
>> traffic.
>
> Your wallet, but is it viable?
Well, the motor concept came first - scooter from teenage memories.
No wallet mostly used as moth repository, but have machine shop.
>
>> Step #3 has to be fitting modern disc brakes.
>
> A well setup drum brake, and very good forward planning ;-)
My guess is I would have a 50/50 chance of survival WITH perfect brakes, 50
minute survival with drums.
(that might be a joke, might not)
>
>> Step #4 then has to be upgrading the front suspension, which is where I
>> will run into big problems. The headstock is rigid enough and can be
>> further braced, but the forks are an inverted "Y" folded back slightly
>> with leading arms and short spring/damper units (parts bin engineering
>> from the manufacturer's motorcycle rear suspension)
>> My current thought is to make a more conventional motorcycle front end
>> with two triple plates only with much shorter sliding tube forks.
>> Has anyone got experience with front forks (say 250cc-350cc size) and
>> the possibilities of shortening them?
>
> Have a scout round a breakers and see if anything vaguely modern could be
> adapted to fit. Once you have a stem/bearing set that fits, look very
> carefully at the yoke offset needed from the stem.
No problem machining up yokes as I have the gear - the only forks I've
seen that might be near the length are childrens offroad bikes. They
wouldn't
take the weight.
Greg.Procter
wrote:
> On Oct 11, 2:08ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> My present project is restoring an old motorscooter.
>
> Step #1: SELL the old motorscooter to somebody who likes that
> particular brand.
>
> Those people are definitely OUT THERE, in more ways than one.
I'm definitely "out THERE" ;-)
>
> Step #2: Buy an old motorcycle that you can afford, preferably one
> that was mass produced in Japan and imported by the millions into NZ.
>
I want a scooter because I lost right leg in a motorcycle accident ..
years ago. no real circulation in the bit I have left so need shelter.
So much family stress m/c out but apparently scooters are acceptable.
(I'm going with the flow for now)
> Step #3: Fix it up, using aftermarket repair parts that you can easily
> order from the interweb.
>
>> My current thought is to make a more conventional motorcycle front end
>> with two triple plates only with much shorter sliding tube forks.
>
> Step #4: Next time you have such a creative thought, JUST LET IT GO.
>
>> Has anyone got experience with front forks (say 250cc-350cc size) and
>> the possibilities of shortening them?
>
> Sure. You could install shorter stanchion tubes, shorter springs and
> maybe even shorten the damper rods.
>
> But it wouldn't be worth your time if you have the money to buy a real
> motorcycle that does what you want.
No, can't find such a beast!
>
> And, if you don't have any money, the project will be just an exercise
> in futility if some engine part or rear drive part gives you trouble.
I can make those.
>
> Then you'd be back in here asking about motorcycle engines that you
> could easily adapt to motor scooter style rear drive, or how to adapt
> a motorcycle swing arm and a motorcycle engine to an old scooter.
>
There's the basis of the idea - the particular scooter has a proper
swing arm and a conventional unit construction motor.
Almost anything not too tall in the way of engines could be slotted
in - width about 350mm inside body.
Greg.Procter
<totallyde...@yahoo.co.uk> wrote:
> 1949 Whizzer <macm...@gmail.com> wrote:
>
>> Sure. You could install shorter stanchion tubes, shorter springs and
>> maybe even shorten the damper rods.
>
> Or you could do what I suggest, which is raise them through the yokes.
> As long as you don't mind maybe a couple of inches of stanchion poking
> up.
>
Can't do it - the body/front skirt surrounds the head.
Greg.Procter
wrote:
> On Oct 11, 9:06ï¿œpm, totallydeadmail...@yahoo.co.uk (Looking for an
Let's put it this way - I started tuning bikes in the mid 60s,
started building frames and engines in the late 1960s. Racing bikes
1969. (eyesight not up to racing speeds so I retreated to building/tuning)
End of 1970s m/c accident ended m/c career.
1990s worked with John Britten on engine concepts.
I can design a motor, I can design a frame.
I don't know the current and recent motorcycles.
I don't have deep pockets.
Have lathes and mills, CNC and conventional.
Regards,
Greg.P.
Greg.Procter
<totallyde...@yahoo.co.uk> wrote:
> 1949 Whizzer <macm...@gmail.com> wrote:
>
>>
>> And, if he found a set of forks for a more modern motorcycle which
>> used a 17-inch front wheel,
>
> Who said he would?
>
Adapting "X" axle and wheel to "Y" forks is no problem.
I could equally design completely new forks and machine them,
but if existing forks could be shortened it would cut costs drastically.
Greg.Procter
<totallyde...@yahoo.co.uk> wrote:
> Schiffner <steven...@hotmail.com> wrote:
>
>> On Oct 11, 10:06 pm, totallydeadmail...@yahoo.co.uk (The Older
>> Gentleman) wrote:
>> > 1949 Whizzer <macmi...@gmail.com> wrote:
>> > > Sure. You could install shorter stanchion tubes, shorter springs and
>> > > maybe even shorten the damper rods.
>> >
>> > Or you could do what I suggest, which is raise them through the yokes.
>> > As long as you don't mind maybe a couple of inches of stanchion poking
>> > up.
>>
>> uh, dude your senility is creeping in methinks...he's talking about a
>> motor-scooter.
>
> My bad for not reading the post properly. That said, grafting a
> conventional front fork end on wouldn't be hard: just a waste of effort.
>
I don't mind wasting effort - retired with more sense than money :-)
little man upon the stair
> Haven't bought it yet - have put in an auction bid though.
In that case, don't buy it, look for something that does what you want
without
having to make major modifications.
Personally, I was thinking about buying a 3-wheeled bicycle and adding
a 49cc moped motor to it if I ever deteriorate to the point where I
can no longer balance a 2-wheeler...
little man upon the stair
> 1990s worked with John Britten on engine concepts.
I saw Stroud race the Britten at Daytona and Laguna Seca in 1994.
It was an awesome piece of machinery that gobbled up other motorcycles
like Pac-Man gobbling yellow dots...
little man upon the stair
> Adapting "X" axle and wheel to "Y" forks is no problem.
> I could equally design completely new forks and machine them,
> but if existing forks could be shortened it would cut costs drastically.
You'd have to adapt a smaller diameter scooter wheel (maybe a 12~14
incher) to any motorcycle fork that you might find.
The typical small motorcycle front wheel just wouldn't fit under the
front "fender" of an NZeta...
Greg.Procter
<macm...@gmail.com> wrote:
Nothing on the NZ market that I can afford suits - anyway, I have fond
memories
of the scooter ...
I live rurally beside State Highway 1 so _anything_ I buy has to do 60mph
inside 30 seconds or I'm toast. Sure, I can ride a 2 wheel bicycle or a
scooter.
Greg.Procter
<macm...@gmail.com> wrote:
The original wheel is sufficient - 12" and there's just room for
two yokes below the head. Machining up yokes is not a problem
and gives me the chance to increase the trail. (curreently 75mm/3")
Modifying other forks would make fitting a disk brake easy.
Didn't think of Wikipaedia, must have a look!
Greg.Procter
<macm...@gmail.com> wrote:
I worked with John on the follow-up motor. Sadly he went and died of
cancer before it was built. Seems to have reappeared on the Chch
"jetpack" flying thingy, but I wasn't part of that.
Did put a bit of thought into the V twin but there wasn't much more bhp to
be had.
Greg.P.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 22, 7:22ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> Adapting "X" axle and wheel to "Y" forks is no problem.
>> I could equally design completely new forks and machine them,
>> but if existing forks could be shortened it would cut costs drastically.
>
> You'd have to adapt a smaller diameter scooter wheel (maybe a 12~14
> incher) to any motorcycle fork that you might find.
>
> The typical small motorcycle front wheel just wouldn't fit under the
> front "fender" of an NZeta...
>
"fender"? is that like "mudguard" or "front bumper"?
The dividing line is the chrome strip - petrol tank above, metal below
is frame. (well, upright sheet metal, rolled bottom edge, "L" top edge)
There's 6"/150mm of wheel travel and still several inches of extra space.
paul c
> On Fri, 23 Oct 2009 15:36:43 +1300, little man upon the stair
> <macm...@gmail.com> wrote:
>
>>
>>> Adapting "X" axle and wheel to "Y" forks is no problem.
>>> I could equally design completely new forks and machine them,
>>> but if existing forks could be shortened it would cut costs drastically.
>>
>> You'd have to adapt a smaller diameter scooter wheel (maybe a 12~14
>> incher) to any motorcycle fork that you might find.
>>
>> The typical small motorcycle front wheel just wouldn't fit under the
>> front "fender" of an NZeta...
>>
>> http://en.wikipedia.org/wiki/%C4%8Cezeta
>>
>
> The original wheel is sufficient - 12" and there's just room for
> two yokes below the head. Machining up yokes is not a problem
> and gives me the chance to increase the trail. (curreently 75mm/3")
> Modifying other forks would make fitting a disk brake easy.
>
> Didn't think of Wikipaedia, must have a look!
(Thanks for the marque name, interesting photos here and there on the
web. I've never seen a Cezeta/Nzeta in person but it reminds of a number
of Euro scoots from that era.) I was wondering if you'd have to change
rake and therefore trail, maybe better high-speed stability is what you
have in mind but personally I wouldn't want to change the low-speed
behaviour. If the main goal is stronger braking, an alternative might
be to consider beefing up the stock forks to mount a disc and caliper,
maybe similar to the way the leading-link Ural models do it, plus
possibly heavier shock and spring since they probably need replacement
anyway.
little man upon the stair
> I was wondering if you'd have to change
> rake and therefore trail, maybe better high-speed stability is what you
> have in mind but personally I wouldn't want to change the low-speed
> behaviour.
It's not a good idea to try going faster than about 50 mph on a
scooter with moderate sized wheels, because the diameter of the tire
not only affects handling, it affects ride quality and traction as the
tire rolls over tiny bumps in the pavement.
Some of the larger scooters have gone to 18-inch wheels to manage the
bump problem.
The Older Gentleman
> On Oct 23, 7:37 am, paul c <toledobythe...@oohay.ac> wrote:
>
> > I was wondering if you'd have to change
> > rake and therefore trail, maybe better high-speed stability is what you
> > have in mind but personally I wouldn't want to change the low-speed
> > behaviour.
>
> It's not a good idea to try going faster than about 50 mph on a
> scooter with moderate sized wheels, because the diameter of the tire
> not only affects handling, it affects ride quality and traction as the
> tire rolls over tiny bumps in the pavement.
More nonsense. Ever ridden any of the new generation of super-scoots?
No, thought not. I rode a 400 Burgman a couple of years ago. Opened my
mind. Damn thing did over 90 and handled really well.
And if you think about it (which you don't) your complaint would apply
to every single bike with (say) wheels of 16" or less, not just
scooters.
>
> Some of the larger scooters have gone to 18-inch wheels to manage the
> bump problem.
And some go just fine on smaller ones. And in any case, the real problem
with smaller wheels is the twitchiness of them.
You know nothing.
--
BMW K1100LT Ducati 750SS Honda CB400F Triumph Street Triple
Suzuki TS250ER (currently Beaving) Damn, back to five bikes!
little man upon the stair
wrote:
> You know nothing.
You prove that you know less every time you challenge an obvious fact.
The Older Gentleman
little man upon the stair
Cottager) pled:
> Nope, sweetie-pie. Wrong again.
It doesn't matter how much you beg, I'm not going to explain the
effects of
vibrational frequency on traction as regards rubber tires beyond
saying that, when the vibration stops, you're about to crash.
The Older Gentleman
> On Oct 23, 3:44?pm, totallydeadmail...@yahoo.co.uk (The Importunate
Right. So all small-wheeled bikes are dangerous.
Do you have a minimum size that you consider to be safe? If so, what? We
need to know.
little man upon the stair
Sniveller) wrote:
> Do you have a minimum size that you consider to be safe? If so, what? We
> need to know.
Who's this "we" you're referring to? Are you in bed with Spacker
again?
Greg.Procter
I think changing the rake would be more than I'm prepared to attempt,
given that it's set by and within the body structure. It shouldn't be
hard to increase the trail a fraction. (it's 75mm/3") Either making new
and extended leading links or triple plates if I go with alternative
front forks.
The "Y" fork structure might be rigid enough, but I'm only going to find
out at the worst possible moments! The standard spring/damper units are
simply CZ long travel rear spring/damper units and presumably will
be long past their prime.
Greg.P.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 23, 7:37ï¿œam, paul c <toledobythe...@oohay.ac> wrote:
>
>> ï¿œI was wondering if you'd have to change
>> rake and therefore trail, maybe better high-speed stability is what you
>> have in mind but personally I wouldn't want to change the low-speed
>> behaviour.
>
> It's not a good idea to try going faster than about 50 mph on a
> scooterï¿œwith moderate sized wheels, because the diameter of the tire
> not only affects handling, it affects ride quality and traction as the
> tire rolls over tiny bumps in the pavement.
>
> Some of the larger scooters have gone to 18-inch wheels to manage the
> bump problem.
>
My NZeta in the 1960s was quite stable at up to around 70mph.
(down-hill, tailwind and prayer ;-)
That's really (one of) the reasons I'm interested in rebuilding one.
PS handbook claimed 59mph top speed (95km/hr) and I regularly achieved
65mph on the speedo. (eventually)
The upside down bathtub structure is/was extremely rigid and the
long-travel suspension handled local conditions very well.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 23, 11:31ï¿œam, totallydeadmail...@yahoo.co.uk (The Evil Clown)
> wrote:
>
>> You know nothing.
>
> You prove that you know less every time you challenge an obvious fact.
>
I've ridden may bikes with much worse handling than the NZeta scooter,
eg Harleys, worn Nortons, Triumphs ...
Greg.P.
Greg.Procter
<totallyde...@yahoo.co.uk> wrote:
> little man upon the stair <macm...@gmail.com> wrote:
>
>> On Oct 23, 3:44?pm, totallydeadmail...@yahoo.co.uk (The Importunate
>> Cottager) pled:
>>
>> > Nope, sweetie-pie. Wrong again.
>>
>> It doesn't matter how much you beg, I'm not going to explain the
>> effects of
>> vibrational frequency on traction as regards rubber tires beyond
>> saying that, when the vibration stops, you're about to crash.
>
> Right. So all small-wheeled bikes are dangerous.
>
> Do you have a minimum size that you consider to be safe? If so, what? We
> need to know.
>
27" rims are generally safe!
;-)
- Bigger wheels don't fall into big pot-holes as badly as small ones.
- Smaller wheels give better acceleration. ;-)
- Smaller wheels have less gyroscopic effect. (rider/bike stability)
most other effects relate more to suspension than size.
Greg.P.
little man upon the stair
> 27" rims are generally safe!
Modern sportbikes have tires with an outer diameter of 22 to 25
inches, anything smaller will lose traction on all but billiard-smooth
pavement and anything larger than 25 inch diameter will out-track
badly when the rider tries to turn into a corner.
> - Bigger wheels don't fall into big pot-holes as badly as small ones.
> - Smaller wheels give better acceleration. ;-)
> - Smaller wheels have less gyroscopic effect. (rider/bike stability)
> most other effects relate more to suspension than size.
I got heavy into this business several years ago and was the OP that
started this thread.
I got into the vibration problem in the first message and went on to a
study of spring preload and how to adjust sag to avoid hobby-horsing
over bumps at the desired cruising speed.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 24, 6:31ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> 27" rims are generally safe!
>
> Modern sportbikes have tires with an outer diameter of 22 to 25
> inches, anything smaller will lose traction on all but billiard-smooth
> pavement
That would be a matter of suspension rather than tyre diameter. (down to a
point where the radius is greater than about 1/3rd the depth of ruts,
holes and corrugations)
A lighter wheel can obviously follow irregularities quicker than a heavier
wheel. (sprung vs unsprung weight)
and anything larger than 25 inch diameter will out-track
badly when the rider tries to turn into a corner.
Is there something magic about 25"?
>
>> - Bigger wheels don't fall into big pot-holes as badly as small ones.
>> - Smaller wheels give better acceleration. ;-)
>> - Smaller wheels have less gyroscopic effect. (rider/bike stability)
>> most other effects relate more to suspension than size.
>
> I got heavy into this business several years ago and was the OP that
> started this thread.
>
> http://groups.google.com/group/alt.motorcycle.sportbike/browse_thread/thread/47927af34e5a9560/6476145991efd6f5?hl=en&lnk=gst&q=%22good+vibrations%22#6476145991efd6f5
>
> I got into the vibration problem in the first message and went on to a
> study of spring preload and how to adjust sag to avoid hobby-horsing
> over bumps at the desired cruising speed.
"Hobby-horsing"? (rebound(?))
(Sorry, possible language problem there)
Have you considered damping rates???
Regards,
Greg.P.
Greg.Procter
<macm...@gmail.com> wrote:
It strikes me that you are concerned with how to get the best performance
from existing suspension systems, rather than how to build the best/ most
practical suspension. (practical vs theory) That's fair enough.
One's theoretical motorcycle and rider must cope with both raised bumps
and dips in the surface. My theory says the suspension needs to be set
mid-point in it's travel with the bike normally laden at rest.
The standard of the road surface will dictate whether one wants that rest
point to be above or below the half way point. The length of movement,
vehicle speed and spring rate determines the spring design.
Preload is something to be considered when attempting to improve
an existing suspension. With zero unsprung weight (unachievable)
one would need (almost) no spring preload.
One needs the wheel to remain in direct, weighted contact with the
road surface, but the unsprung to sprung weight ratio in conjunction with
the change in spring pressure with the extension due to that movement
affects the rate at which the suspension will move. (also of course the
rate at which the bike and rider move vertically)
Coil springs are effectively torsion springs which have (almost) no
rebounce. (naturally damped) Of course, the total suspension design etc
means that dampers are required.
I remember riding on an old concrete slab road where each slab was slightly
tilted. I watched the front wheel rise and fall over each slab and settle
a tiny fraction higher each time (somewhat higher speed than legally
acceptable)
Eventually the suspension hit the top stop and I was forced to back off.
Watching the suspension rebound was also interesting!
little man upon the stair
> That would be a matter of suspension rather than tyre diameter. (down to a
> point where the radius is greater than about 1/3rd the depth of ruts,
> holes and corrugations)
Back in the late 1960's, most of the motorcycles known as
"scramblers" and "enduros" which were available to the off-road
enthusiasts in America had 19-inch front wheels.
We were amazed by the improvement in ride and precise steering offered
by the
21-inch front wheels that European motocrossers favored.
The outside diameter of the tire on the 21-inch wheel really wasn't
larger than the
outside diameter of the 19-inch wheel, but Honda caught on to the
possibility of larger diameter wheels and equipped one model with 23-
inch wheels.
That only lasted one or two model years on their XR models in the
1970's...
> "Hobby-horsing"?
Don't parents give their kids rocking horse down in NZ?
When your front wheel hits a bump, it compresses the spring and
compression damping and the ratio of sprung to unsprung weight play a
role in limiting the upward movement of the handlebars.
But the handlebars are connected to the chassis and a certain moment
is transferred through the springs and rear dampers to the rear wheel
*before it hits the same bump that deflected the front wheel.
Then the rear wheel hit the same bump a fraction of a second later and
the process is reversed as the bump is transmitted back through the
chassis to the front wheel and this chassis rocking is called "hobby-
horsing".
> Have you considered damping rates???
Hydraulic dampers cannot work if there is very little motion of the
fork or shock.
In order to eliminate hobby-horsing on California freeways, one has to
carefully adjust front spring sag so it's about twice what you'd use
on the rear springs.
.
little man upon the stair
> badly when the rider tries to turn into a corner.
>
> Is there something magic about 25"?
No, it's not magic, the optimum tire size and weight distributions of
modern sport bikes have been arrived at by trial and error and the
perceptions by experienced riders as to what feels right to them.
We saw sportbike manufacturers adopt 16-inch front wheels in the early
1980's to speed up steering response. But motorcycles equipped with 16-
inch front wheels would not recover from a front tire washout, the
riders could expect to crash.
The 17-inch front wheel has been universally adopted as the standard
for sportbikes.
But some professional GP riders like 16.5-inch wheels for the quicker
steering.
little man upon the stair
> It strikes me that you are concerned with how to get the best performance
> from existing suspension systems, rather than how to build the best/ most
> practical suspension. (practical vs theory) That's fair enough.
Most sportriders have no interest in designing a motorcycle, they just
want to get their machine's suspension system adjusted so they can
ride with their friends.
When they read the recommendations of the motorcycle magazines, which
are made by expert riders after riding around a race track that they
know very well, the recommendations will be for a race track set up
which will not be very comfortable on California's rough freeways,
where each pavement section is set at
a slightly different angle than the next.
Even in cases where the freeway was paved in one continuous pour of
concrete, which is brushed to enhance traction before it dries, the
pavement will have height irregularities.
When attempting to ride on freeways so paved with a race track
suspension set up, I encountered eyeball jiggling so bad that I
couldn't focus on distant objects.
When I backed off spring preload to the point where half the travel
was used up in sag, suddenly turning into a tight corner resulted in
severe out tracking as weight transferred to the front tire.
> One's theoretical motorcycle and rider must cope with both raised bumps
> and dips in the surface. My theory says the suspension needs to be set
> mid-point in it's travel with the bike normally laden at rest.
Race track set ups usually recommend that front spring sag be
somewhere between 25% and 33% of the total travel. I wound up with
about 40% sag as the best compromise.
Also, the Bridgestone BT-020 sport touring tire that I was using was
about one inch larger in diameter due to a taller sidewall.
I changed to a tire which more closely resembled the favored sporty
sport tire
profile and diameter to eliminate the out tracking, which was always
noticeable at
any speed.
> I remember riding on an old concrete slab road where each slab was slightly
> tilted. I watched the front wheel rise and fall over each slab and settle
> a tiny fraction higher each time (somewhat higher speed than legally
> acceptable)
> Eventually the suspension hit the top stop and I was forced to back off.
> Watching the suspension rebound was also interesting!
Your front suspension was packing down because the fork oil was too
thick.
Damper rod type forks are very sensitive to fork oil weight, that's
why cartridge forks with their stacks of flexible washers to act as a
variable orifice were invented.
And the Gold Valve Emulators offered by Race Tech are a much cheaper
alternative to buying a whole new cartridge fork to replace a damper
rod fork.
Of couse the ultimate fork would be an Ohlins, with damping that's
adjustable at
both high stroking speeds and low stroking speeds.
Nevertheless, a hydraulic damping system cannot damp motion very well
if the
suspension units aren't moving quite a bit.
Then traction reverts back to the tire contact patch and the damping
caused molecular friction (aka "hysteresis") in the rubber has to do
all the work of absorbing those tiny bumps that may only be 1/4 of an
inch high.
And larger diameter tires will do a much better job than a small
diameter tire in such cases.
But, consider a go kart chassis which has no suspension at all. The go
kart driver expects to be turning constantly and he *wants* his rear
tires to be "loose" so he can turn rapidly.
Mini-bikes often have tires that are about the size of go-kart tires
and some of the smaller scooters have tires that aren't much bigger,
so they will feel "loose" at rather low speeds, compared to the speeds
that I ride my sportbike at on the highway.
The Older Gentleman
> We saw sportbike manufacturers adopt 16-inch front wheels in the early
> 1980's to speed up steering response. But motorcycles equipped with 16-
> inch front wheels would not recover from a front tire washout, the
> riders could expect to crash.
Actually, the 16" wheel problem was only a problem on bikes that had not
been designed for such a front wheel. Manufacturers just shoved them
onto bikes with little or no other chassis changes - Suzuki did, Guzzi
did... I'll bet you never rode a Guzzi T5 or Mark Four Le Mans.
On bikes designed for such wheels, they worked. GPZ900R, anyone?
And your ignorance means you don't appear to know about the
all-conquering 1990s sports bike, that came with a 16" front wheel: the
original Fireblade.
The Older Gentleman
> Modern sportbikes have tires with an outer diameter of 22 to 25
> inches, anything smaller will lose traction on all but billiard-smooth
> pavement
Utter, utter nonsense.
The Older Gentleman
I thought that was your 'thing'. No, come on, this being a tech forum,
we really need to know what 'moderate sized wheels' are. What diameter?
Because obviously we don't want to be unsafe, do we?
The Older Gentleman
> Mini-bikes often have tires that are about the size of go-kart tires
> and some of the smaller scooters have tires that aren't much bigger,
Ah, so we're talking about six-inch diameter wheels, now?
Rather a different kettle of fish. Not 'moderate' sized wheels, which is
what you first banged on about. So you're moving the goalposts. It
happened quicker than I expected.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 24, 7:45ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> It strikes me that you are concerned with how to get the best
>> performance
>> ï¿œfrom existing suspension systems, rather than how to build the best/
>> most
>> practical suspension. (practical vs theory) That's fair enough.
>
> Most sportriders have no interest in designing a motorcycle, they just
> want to get their machine's suspension system adjusted so they can
> ride with their friends.
Of course, but one needs to understand how the system of wheels,suspension
and geometry work if one wants to make real improvements.
I'm in the situation of a near blank drawing board with only rake and
wheel size fixed. Admittedly, the original suspension worked exceptionally
well, but I'm uncomfortable with it's strength. (or apparent lack of
strength for the use I intend for it)
>
> When they read the recommendations of the motorcycle magazines, which
> are made by expert riders after riding around a race track that they
> know very well, the recommendations will be for a race track set up
> which will not be very comfortable on California's rough freeways,
> where each pavement section is set at
> a slightly different angle than the next.
>
> Even in cases where the freeway was paved in one continuous pour of
> concrete, which is brushed to enhance traction before it dries, the
> pavement will have height irregularities.
>
> When attempting to ride on freeways so paved with a race track
> suspension set up, I encountered eyeball jiggling so bad that I
> couldn't focus on distant objects.
>
> When I backed off spring preload to the point where half the travel
> was used up in sag, suddenly turning into a tight corner resulted in
> severe out tracking as weight transferred to the front tire.
>
I'm not really sure what you mean by "out-tracking"?
(perhaps the infamous separation of two cultures by language :-)
>> One's theoretical motorcycle and rider must cope with both raised bumps
>> and dips in the surface. My theory says the suspension needs to be set
>> mid-point in it's travel with the bike normally laden at rest.
>
> Race track set ups usually recommend that front spring sag be
> somewhere between 25% and 33% of the total travel. I wound up with
> about 40% sag as the best compromise.
>
Yes, that sounds about right.
> Also, the Bridgestone BT-020 sport touring tire that I was using was
> about one inch larger in diameter due to a taller sidewall.
>
> I changed to a tire which more closely resembled the favored sporty
> sport tire
> profile and diameter to eliminate the out tracking, which was always
> noticeable at
> any speed.
>
>> I remember riding on an old concrete slab road where each slab was
>> slightly
>> tilted. I watched the front wheel rise and fall over each slab and
>> settle
>> a tiny fraction higher each time (somewhat higher speed than legally ￜ
>> acceptable)
>> Eventually the suspension hit the top stop and I was forced to back off.
>> Watching the suspension rebound was also interesting!
>
> Your front suspension was packing down because the fork oil was too
> thick.
Bear in mind that that stretch of road is the only concrete slab road
I know of in New Zealand. I never felt the need to change damping rates
elsewhere in NZ.
>
> Damper rod type forks are very sensitive to fork oil weight, that's
> why cartridge forks with their stacks of flexible washers to act as a
> variable orifice were invented.
>
> And the Gold Valve Emulators offered by Race Tech are a much cheaper
> alternative to buying a whole new cartridge fork to replace a damper
> rod fork.
>
> Of couse the ultimate fork would be an Ohlins, with damping that's
> adjustable at
> both high stroking speeds and low stroking speeds.
>
> Nevertheless, a hydraulic damping system cannot damp motion very well
> if the
> suspension units aren't moving quite a bit.
>
> Then traction reverts back to the tire contact patch and the damping
> caused molecular friction (aka "hysteresis") in the rubber has to do
> all the work of absorbing those tiny bumps that may only be 1/4 of an
> inch high.
>
> And larger diameter tires will do a much better job than a small
> diameter tire in such cases.
I'm stuck with the original wheel diameter of 12" plus 3.50 - 19"
overall diameter. That factor is fixed for authenticity.
>
> But, consider a go kart chassis which has no suspension at all. The go
> kart driver expects to be turning constantly and he *wants* his rear
> tires to be "loose" so he can turn rapidly.
The cart has two driven tyres on a rigid axle the ground and generally
a much smoother surface than I drive on.
>
> Mini-bikes often have tires that are about the size of go-kart tires
> and some of the smaller scooters have tires that aren't much bigger,
> so they will feel "loose" at rather low speeds, compared to the speeds
> that I ride my sportbike at on the highway.
>
As I say, my wheel diameter is fixed - I need the suspension to do the
work.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 24, 7:15ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> That would be a matter of suspension rather than tyre diameter. (down
>> to a
>> point where the radius is greater than about 1/3rd the depth of ruts,
>> holes and corrugations)
>
> Back in the late 1960's, most of the motorcycles known as
> "scramblers" and "enduros" which were available to the off-road
> enthusiasts in America had 19-inch front wheels.
>
> We were amazed by the improvement in ride and precise steering offered
> by the
> 21-inch front wheels that European motocrossers favored.
We went with the Europeans, but I always thought the US market was
poking itself in the eye demanding the smaller front wheels.
>
> The outside diameter of the tire on the 21-inch wheel really wasn't
> larger than the
> outside diameter of the 19-inch wheel, but Honda caught on to the
> possibility of larger diameter wheels and equipped one model with 23-
> inch wheels.
>
> That only lasted one or two model years on their XR models in the
> 1970's...
>
>> "Hobby-horsing"?
>
> Don't parents give their kids rocking horse down in NZ?
I certainly fell on my head from one of those - nowdays I think they
are becoming PC incorrect ;-)
>
> When your front wheel hits a bump, it compresses the spring and
> compression damping and the ratio of sprung to unsprung weight play a
> role in limiting the upward movement of the handlebars.
>
> But the handlebars are connected to the chassis and a certain moment
> is transferred through the springs and rear dampers to the rear wheel
> *before it hits the same bump that deflected the front wheel.
>
> Then the rear wheel hit the same bump a fraction of a second later and
> the process is reversed as the bump is transmitted back through the
> chassis to the front wheel and this chassis rocking is called "hobby-
> horsing".
It's just the different terminology - plus of course you yanks have tended
to have heavier and softer sprung m/cs which would be more prone to such
antics.
>
>> Have you considered damping rates???
>
> Hydraulic dampers cannot work if there is very little motion of the
> fork or shock.
>
> In order to eliminate hobby-horsing on California freeways, one has to
> carefully adjust front spring sag so it's about twice what you'd use
> on the rear springs.
Different road conditions here :-)
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 24, 7:15ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>> On Sun, 25 Oct 2009 15:00:40 +1300, little man upon the stair ￜ
>> and anything larger than 25 inch diameter will out-track
>> ￜ badly when the rider tries to turn into a corner.
>>
>> Is there something magic about 25"?
>
> No, it's not magic, the optimum tire size and weight distributions of
> modern sport bikes have been arrived at by trial and error and the
> perceptions by experienced riders as to what feels right to them.
Of course. But what you perceive may be different to my perception
thereof. Also, I'm aiming at a much lighter bike that that which you
might consider a "normal" sports bike.
(With only one leg, I can't pick up a dropped 700lb bike. 300-400lb
would be my absolute maximum)
>
> We saw sportbike manufacturers adopt 16-inch front wheels in the early
> 1980's to speed up steering response. But motorcycles equipped with 16-
> inch front wheels would not recover from a front tire washout, the
> riders could expect to crash.
>
> The 17-inch front wheel has been universally adopted as the standard
> for sportbikes.
>
> But some professional GP riders like 16.5-inch wheels for the quicker
> steering.
>
--
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
little man upon the stair
> I'm not really sure what you mean by "out-tracking"?
> (perhaps the infamous separation of two cultures by language :-)
You Kiwis still keep left on the roads, don't you?
Imagine you're riding on a curvy road in the hills and you're trying
to see around a
hill that blocks your view of oncoming traffic, so you're riding near
the center dividing line to see whatever is coming at you sooner.
So you see the lorry coming around the bend and he's taking up more
than his share of the road and you countersteer by pushing the left
hand bar forward.
If the scooter initially out-tracks, the chassis follows the direction
of the front wheel, which is pointed towards the lorry for a
terrifying split second, before the
scooter begins to turn left.
Initial out-tracking is the scary part, and initial weight transfer
makes the out-tracking worse.
There can also be a persistant tendancy to out-track if the front and
rear tires are of different widths and profiles or if the front ride
heigth is too high or the rear ride height is too low.
In the case of persistent out-tracking you'll need to maintain
pressure on the handle bar to keep the scooter from widening it's line
in a curve.
An equally annoying condition is when the motorcycle doesn't out-track
in the least, but tends to fall into the inside of the curve.
Sport riders have to learn to time their countersteering input exactly
so they don't have to countersteer oppositely to keep the motorcycle
from falling into the corner, with a resulting widening of the arc,
followed by yet another input to have another attempt at establishing
the correct line.
Riders may not realize that their problem is front/rear ride height or
a problem with tire profiles and they may insist that they have their
front/rear sag set up correctly and won't want to change it.
That type of rider may also be unwilling to slide the fork stanchion
tubes up and down in the yokes.
So he continues to have to make mid-corner changes in his lines.
That's a safety problem on the street, and is annoying to racers who
are trying to pass him on the track.
There was an engineer at Michelin who came up with a set of formulae
for tire profiles and diameters and coning angles and how everything
related to rack and trail and wheelbase.
I found his name on the interweb once but have never run across his
formulae.
> I'm stuck with the original wheel diameter of 12" plus 3.50 - 19"
> overall diameter. That factor is fixed for authenticity.
That's still a fair bit larger than the tire diameter I had envisioned
when you first mentioned that you wanted motorcycle forks on a
scooter.
I suggest that you go to some of the tire manufacturer's web pages and
see what they have available in that size.
A quick way to get a list of the tire manufacturer's pages is to go to
www.mawonline.com and click on "tires".
This will take you to a list of tire manufacturers and there is an URL
leading to each manufacturer.
> As I say, my wheel diameter is fixed - I need the suspension to do the
> work.
With a smaller diameter tire, the suspension is going to have to work
harder.
A soft rubber compound on the front tire will help the suspension to
deal with the
surface roughness by absorbing the smallest bumps.
The Older Gentleman
> So you see the lorry coming around the bend and he's taking up more
> than his share of the road and you countersteer by pushing the left
> hand bar forward.
>
> If the scooter initially out-tracks, the chassis follows the direction
> of the front wheel, which is pointed towards the lorry for a
> terrifying split second, before the
> scooter begins to turn left.
<snip>
As you've never actually ridden a scooter, let alone on (for you) the
'wrong' side of the road, where does this advice come from?
little man upon the stair
> Of course. But what you perceive may be different to my perception
> thereof. Also, I'm aiming at a much lighter bike that that which you
> might consider a "normal" sports bike.
Are you aware that all the manufacturers have been building very light
sportbikes
since the mid-1990's?
A 1993 Honda CBR900RR weighs about 350 pounds without fluids and a
battery.
The Yamaha YZF-1000R1 that came out around 2000 also weighs about
350~375 dry weight.
What annoys me about the lightweight sportbikes is that they typically
have a
33-inch seat height.
I'm riding around on a 550-pound FZR1000 with a plywood seat so my
feet will reach the ground and keep me from falling over if I get
experience vertigo while stopped for a traffic light.
> (With only one leg, I can't pick up a dropped 700lb bike. 300-400lb
> would be my absolute maximum)
Go to alt.motorcycle.sportbike and start a thread titled "Ping Bob
Nixon".
He has no right leg and still rides a Suzuki SV650. Ask him how he
copes, and he will tell you.
Some of the riders on alt.motorcycle.sportbike would like to hear
about your association with John Britten, too.
paul c
>> ...
> I think changing the rake would be more than I'm prepared to attempt,
> given that it's set by and within the body structure. It shouldn't be
> hard to increase the trail a fraction. (it's 75mm/3") Either making new
> and extended leading links or triple plates if I go with alternative
> front forks.
Okay, you're closer to it than I am. I just assumed that using
non-leading forks would move the wheel rearward so the rake would have
to change. Photos seemed to suggest same, but my eyes aren't too hot,
so maybe I was wrong to think about rake.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 25, 1:23ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> I'm not really sure what you mean by "out-tracking"?
>> (perhaps the infamous separation of two cultures by language :-)
>
> You Kiwis still keep left on the roads, don't you?
Still???
You yanks still drive on the wrong side, don't you?
>
> Imagine you're riding on a curvy road in the hills and you're trying
> to see around a
> hill that blocks your view of oncoming traffic, so you're riding near
> the center dividing line to see whatever is coming at you sooner.
>
> So you see the lorry coming around the bend and he's taking up more
> than his share of the road and you countersteer by pushing the left
> hand bar forward.
>
> If the scooter initially out-tracks, the chassis follows the direction
> of the front wheel, which is pointed towards the lorry for a
> terrifying split second, before the
> scooter begins to turn left.
>
> Initial out-tracking is the scary part, and initial weight transfer
> makes the out-tracking worse.
Hmmm, seems I always rode the wrong sorts of bikes - toss your weight the
way you want to go and the bike goes that way.
The technique probably requires that the rider has his feet under his/her
centre of gravity. It always worked for me!
>
> There can also be a persistant tendancy to out-track if the front and
> rear tires are of different widths and profiles or if the front ride
> heigth is too high or the rear ride height is too low.
>
Silly design for motorbikes!
That's why I'm interested in the particular model - plus there's only
a partial dip between steering head and seat rather than the usual "U"
spring frame design that comes from a flat floor.
It's a very rigid scooter. (one might say overengineered)
>
> I suggest that you go to some of the tire manufacturer's web pages and
> see what they have available in that size.
>
> A quick way to get a list of the tire manufacturer's pages is to go to
> www.mawonline.com and click on "tires".
>
> This will take you to a list of tire manufacturers and there is an URL
> leading to each manufacturer.
>
>> As I say, my wheel diameter is fixed - I need the suspension to do the
>> work.
>
> With a smaller diameter tire, the suspension is going to have to work
> harder.
>
> A soft rubber compound on the front tire will help the suspension to
> deal with the
> surface roughness by absorbing the smallest bumps.
>
--
Greg.Procter
<totallyde...@yahoo.co.uk> wrote:
> little man upon the stair <macm...@gmail.com> wrote:
>
>> So you see the lorry coming around the bend and he's taking up more
>> than his share of the road and you countersteer by pushing the left
>> hand bar forward.
>>
>> If the scooter initially out-tracks, the chassis follows the direction
>> of the front wheel, which is pointed towards the lorry for a
>> terrifying split second, before the
>> scooter begins to turn left.
>
> <snip>
>
> As you've never actually ridden a scooter, let alone on (for you) the
> 'wrong' side of the road, where does this advice come from?
>
The "driving side of the road" doesn't make much difference to the
handling,
other than when one goes against the flow, when it makes a considerable
difference!
As to road surfaces, it's hard to make absolute comparisons because not
all US roads are the same and not all NZ roads are the same :-)
However, we have half the population density of the US and the country
is generally lumpy.
Where I live is geographically near a sub-join between the Pacific and
Australian techtonic plates with the two crunching upwards.
In addition the region is made up of recent volcanic activity so the soil
is very unstable - the roads are always moving. (slowly) Result paved but
uneven surfaces, hills and valleys and regular 45-50mph bends on 60mph
roads.
Greg.Procter
Rake seems adequate. Triple clamps are easy to mill to set the trail.
(advantages of having CNC mill in workshop)
In fact, the axle and head would have (exactly) the same relationship
whether leading link or telescopic were used. The leading link design
appears to have been used by the designers so they could use "parts-
bin" rear suspension units rather than making new telescopic forks.
As my motor design will have vastly more power and stopping distances
have become more critical in the 50 odd years since the original design,
I think the forks strength might be suspect.
Greg.P.
little man upon the stair
> Where I live is geographically near a sub-join between the Pacific and
> Australian techtonic plates with the two crunching upwards.
> In addition the region is made up of recent volcanic activity so the soil
> is very unstable - the roads are always moving. (slowly) Result paved but
> uneven surfaces, hills and valleys and regular 45-50mph bends on 60mph
> roads.
North Island or South Island? BrianNZ is always ranting and raving
about drinking in the pubs and hooning around near New Plymouth over
on rec.motorcycles.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 25, 7:13ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> Where I live is geographically near a sub-join between the Pacific and
>> Australian techtonic plates with the two crunching upwards.
>> In addition the region is made up of recent volcanic activity so the
>> soil
>> is very unstable - the roads are always moving. (slowly) Result paved
>> but
>> uneven surfaces, hills and valleys and regular 45-50mph bends on 60mph ￜ
>> roads.
>
> North Island or South Island? BrianNZ is always ranting and raving
> about drinking in the pubs and hooning around near New Plymouth over
> on rec.motorcycles.
I'm in the far North (AKA Northland) All dairying and pot-growing.
New Plymouth is waaay south of here on the sides and base of a volcano
that is the spitting image of Mt.Fujiama. (ie much flatter)
little man upon the stair
> On Mon, 26 Oct 2009 10:28:15 +1300, little man upon the stair
> <macmi...@gmail.com> wrote:
> Hmmm, seems I always rode the wrong sorts of bikes - toss your weight the
> way you want to go and the bike goes that way.
Professional racers use a lot of upper body strength to countersteer
their racers down to maximum lean angle in a minimum amount of time.
This is called "flicking it into the corner" and it requires a lot of
confidence in available tire grip.
One racer ruefully remarked, "I flicked the bitch and the bitch
flicked me!" after he tried this on cold tires.
> The technique probably requires that the rider has his feet under his/her
> centre of gravity. It always worked for me!
You'll see professional racers sticking a knee out in the direction of
the curve they are about to negotiate, but they have to put their
weight on the outside footpeg to accomplish this.
A Finnish GP racer named Saarinen started hanging his knee out to keep
the motorcycle from sliding out back in the early 1970's and the young
Kenny Roberts started knee dragging in the same period.
Roberts was wearing out his rear tires from spinning them under power
while his mentor the Austrailian Kel Carrauthers was wearing out his
front tires from using the to steer the bike with countersteering.
Gary Nixon rode his racers like Mike Hailwood, his body was always
straight in line with the motorcycle, at whatever lean angle. This
technique was called "ear 'oling" which was to say, "Get yer ear 'ole
as close to the ground as you can."
I used to ride with an "ear 'oler" and it made me nauseous to watch
him leaning over to maximum angles without stick a knee out to catch a
slide.
Nowadays the tall, long-armed ben Spies has been seen dragging his
elbows as lean angles reach 60 degrees from the vertical in MotoGP and
World Superbike races.
> > There can also be a persistant tendancy to out-track if the front and
> > rear tires are of different widths and profiles or if the front ride
> > heigth is too high or the rear ride height is too low.
>
> Silly design for motorbikes!
Motorcycle tire engineers were challenged by the ultra-high speeds
encountered in qualifying on the Daytona Speedway in the early 1970's.
Qualifying involved taking a lap around the tri-oval that NASCAR stock
cars raced on, it did NOT involve diving down into the infield and
negotiating those tight corners at all.
More than one rider made the mistake of failing to peel off for Turn 1
at the start of the actual race, they would continue to head straight
for the banking where they'd qualified.
Anyway, as speeds surpassed 150 mph and reach 175 mph (Agostini
crashed at 175 in 1973) the rear tires would get very hot and they
would lose chunks of rubber.
So rear tires in particular were designed to be wider, with less rain
grooving (or none at all, in the case of a slick tire). The wider
tires had more mass so it would take longer for them to heat up to the
point where the extender oil in the tread would start coming to the
surface and making the tire greasy.
In the early 1980's the tire engineers started designing smaller
diameter front tires as well. The riders needed their motorcycles to
flick in and out of the haybale chicane at the end of the back
straight at Daytona.
Smaller tires worked better for flicking and the engineers would make
them even smaller and narrower if the front tire's rubber could
contain the heat of cornering and braking.
And then it's necessary to consider what the amateur racer or
sportrider is likely to do to a machine that has been set up and
equipped according to the recommendation of experts.
Back in 1986, it was a very common practice for a newbie racer to
install a rear tire that was over an inch wider than the original
equipment tire.
The resulting machine would be harder to turn and the front tire would
have to work harder to deal with the unbalanced traction (front to
rear) while cornering.
The rear tire would have extra traction, and the newbie racer would
lean the machine into a corner, and add a little power, which would
widen his line around the curve.
So he would countersteer a little more to tighten his line. This would
slow the machine down.
So he would add a little more power and countersteer a little more and
add a little power and countersteer a little more until the front tire
suddenly washed out and he crashed.
Then he wonder why he crashed. It was hard to convince a newbie that a
motorcycle that came with a 140mm wide rear tire wasn't going to
behave the same way with a 170mm rear tire on it.
little man upon the stair
> The leading link design
> appears to have been used by the designers so they could use "parts-
> bin" rear suspension units rather than making new telescopic forks.
Well, an Earles fork with rear suspension units is not all that bad an
idea, if you're interested in suspension compliance.
The shock absorber shafts are small diameter, so there's little
stiction compared to a strut type fork.
Problem with an Earles fork is that there is a lot of mass in front of
the steering pivot, so the front end will waggle and hunt on rough
pavement.
I rode a friend's 250cc Greeves MX-5 in the Mojave desert a few times.
It had too much weight on the front tire and the front end waggled and
hunted in the dry sandwashes.
I couldn't go fast enough to get the front tire up on top of the sand,
so the Greeves wallowed along like a pig.
Another Earles fork-equipped machine in those days was the popular
Sachs 125.
Problem was that the front brake drum was anchored to the Earles fork
swing arm, and if the brake was applied it affected suspension
compliance.
Not good, having the brake make the front tire skid early.
The next motorcycle my friend bought bought was a pretty Ossa Stiletto
with conventional forks and much less weight on the front tire. It
handled more like a Yamaha Enduro model like I was riding.
But, by that time, the Japanese had caught onto lightweight
motocrossers with long travel suspensions and those machines could
skitter across the whoop-de-doos like they weren't even there...
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 25, 7:03ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>> On Mon, 26 Oct 2009 10:28:15 +1300, little man upon the stair ￜ
OK, I watched a couple of episodes on chopper building on Sky - rear tyres
about the same width as diameter and front tyres more normal.
Never did see what happened on corners as the obviously couldn't corner ;-)
My personal experience is on much narrower and around 1" difference in
width.
Don't forget that "proper" racing motorcycle tyres are close to triangular
in profile for more grip when heeled over.
Yes, have experienced front wheel heading for the fence under the influence
of power in corners - assumed it was time to back off!
Ordinary road tyres won't grip successfully at racing lean angles, but
normally
there are foot rests, mufflers etc to keep one more upright.
I used to push those limits until one occassion when I had a pillion
passenger
with big boots and minimal brain - we went around the corner in a series of
bumps, straight lines and leaps..
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 25, 7:20ï¿œpm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> The leading link design
>> appears to have been used by the designers so they could use "parts-
>> bin" rear suspension units rather than making new telescopic forks.
>
> Well, an Earles fork with rear suspension units is not all that bad an
> idea, if you're interested in suspension compliance.
>
> The shock absorber shafts are small diameter, so there's little
> stiction compared to a strut type fork.
>
> Problem with an Earles fork is that there is a lot of mass in front of
> the steering pivot, so the front end will waggle and hunt on rough
> pavement.
Err, most of the mass is _behind_ the pivot!
>
> I rode a friend's 250cc Greeves MX-5 in the Mojave desert a few times.
> It had too much weight on the front tire and the front end waggled and
> hunted in the dry sandwashes.
>
> I couldn't go fast enough to get the front tire up on top of the sand,
> so the Greeves wallowed along like a pig.
>
Sounds like there was insufficient trail.
> Another Earles fork-equipped machine in those days was the popular
> Sachs 125.
>
> Problem was that the front brake drum was anchored to the Earles fork
> swing arm, and if the brake was applied it affected suspension
> compliance.
>
> Not good, having the brake make the front tire skid early.
Too true - the front of the bike rises under hard braking as the links
roll around the pivots. Conventional forks sink under hard braking
transfering
weight from rear to front - back wheel locks :-)
>
> The next motorcycle my friend bought bought was a pretty Ossa Stiletto
> with conventional forks and much less weight on the front tire. It
> handled more like a Yamaha Enduro model like I was riding.
>
> But, by that time, the Japanese had caught onto lightweight
> motocrossers with long travel suspensions and those machines could
> skitter across the whoop-de-doos like they weren't even there...
>
Hmmm, Euro off-roaders were ahead of the Japanese, although they tended
to be higher priced specialist bikes. (1960s-70s) Japs eventually made
them cheaper and within a decade just as good.
I wonder if the US experience came from demanding the smaller front
wheels?
The Older Gentleman
> > Problem with an Earles fork is that there is a lot of mass in front of
> > the steering pivot, so the front end will waggle and hunt on rough
> > pavement.
>
> Err, most of the mass is _behind_ the pivot!
That's USKrusty for you: thinks he knows, but doesn't. :-)
Greg.Procter
<totallyde...@yahoo.co.uk> wrote:
> Greg.Procter <pro...@ihug.co.nz> wrote:
>
>> > Problem with an Earles fork is that there is a lot of mass in front of
>> > the steering pivot, so the front end will waggle and hunt on rough
>> > pavement.
>>
>> Err, most of the mass is _behind_ the pivot!
>
> That's USKrusty for you: thinks he knows, but doesn't. :-)
>
The point of the Earles fork, which was invented _after_ the telescopic
fork is a) it's lighter, b) it gets over the telescopic fork problem of
binding under braking.
Older enthusiasts will remember BMW staying with Earles style forks for
years after the market demanded telescopics - they knew what they were
about.
Eventually they were forced by fashion to go to teles.
(I'm not getting into discussions about who knows what - we all know
different things and there's always something to be learned)
Regards,
Greg.P.
The Older Gentleman
> The point of the Earles fork, which was invented _after_ the telescopic
> fork is a) it's lighter, b) it gets over the telescopic fork problem of
> binding under braking.
> Older enthusiasts will remember BMW staying with Earles style forks for
> years after the market demanded telescopics - they knew what they were
> about.
> Eventually they were forced by fashion to go to teles.
So true. And then they nicked the Hossack design (or maybe bought it?)
and everything was nice again.
little man upon the stair
> >> > Problem with an Earles fork is that there is a lot of mass in front of
> >> > the steering pivot, so the front end will waggle and hunt on rough
> >> > pavement.
>
> >> Err, most of the mass is _behind_ the pivot!
Depends on where the spring/shock units are located, which depends on
whether it's a trailing link or a leading link set up.
The inertia of masses disposed in front of, or behind the pivot is
helpful in maintaining stability *while the front tire is firmly
planted on the pavement*.
Once grip is compromised and the fork starts oscillating, the inertia
of the masses will work against a return to stability.
> The point of the Earles fork, which was invented _after_ the telescopic
> fork is a) it's lighter,
That's debatable. I have no doubt that the strut portion of an link
type front suspension can be made lighter than round tubes if it's a
pressed metal welded structure or if it's made from carbon fiber like
Britten used.
b) it gets over the telescopic fork problem of binding under braking.
Yes, the link type fork does away with stiction, but having the link
motion restricted by application of the front brake is as bad or worse
than stiction.
> Older enthusiasts will remember BMW staying with Earles style forks for
> years after the market demanded telescopics - they knew what they were �
> about. Eventually they were forced by fashion to go to teles.
Don't get me wrong. I love the idea of a link-type front suspension,
especially what BMW has done with the latest multi-link front end.
But if *you* want to graft a modern motorcycle front suspension onto
your scooter, you're most probably going to use telescopic struts from
a mass-produced motorcycle after acquirng the parts from a breaker.
I know what it's like to have a machine shop full of lathes and mills
and grinders, but whatever you produce in your shop is going to be one-
off and, if you break it, your motorscooter will be out of commission
until you make a new part.
Greg.Procter
<macm...@gmail.com> wrote:
> On Oct 26, 2:26�pm, "Greg.Procter" <proc...@ihug.co.nz> wrote:
>
>> >> > Problem with an Earles fork is that there is a lot of mass in
>> front of
>> >> > the steering pivot, so the front end will waggle and hunt on rough
>> >> > pavement.
>>
>> >> Err, most of the mass is _behind_ the pivot!
>
> Depends on where the spring/shock units are located, which depends on
> whether it's a trailing link or a leading link set up.
Earles is "leading link".
Trailing link only exists on the odd motorscooter like Vespas. They dive
like hell on braking!
>
> The inertia of masses disposed in front of, or behind the pivot is
> helpful in maintaining stability *while the front tire is firmly
> planted on the pavement*.
Sure, I like to keep mine right there!;-)
(Apparently I don't always do that but ...)
>
> Once grip is compromised and the fork starts oscillating, the inertia
> of the masses will work against a return to stability.
Huhh, why would the wheel start to oscillate when it's clear of the
ground???
>
>> The point of the Earles fork, which was invented _after_ the telescopic
>> fork is a) it's lighter,
>
> That's debatable. I have no doubt that the strut portion of an link
> type front suspension can be made lighter than round tubes if it's a
> pressed metal welded structure or if it's made from carbon fiber like
> Britten used.
No, my bad ... The _sprung weight_ is lighter on an Earles fork than
with telescopic forks. Sprung vs unsprung weight is the vital factor.
>
> b) it gets over the telescopic fork problem of binding under braking.
>
> Yes, the link type fork does away with stiction, but having the link
> motion restricted by application of the front brake is as bad or worse
> than stiction.
>
Err, the telescopic fork has the forces horizontally rearward during
braking.
The rake angle divides that force two forces, a) along the forks. b)
rearward.
depending on the fort angle. The rearward force binds the forks, the upward
force compresses the forks and causes dive. That dive would be much worse
if
the rearward binding force did not exist.
The Earles fork takes all the force rearward. An additional force is
rotational
around the axle - transfered vertically by the link arms to the rigid part
of the
forks and to the frame. The lifting force is approximately countered by
weight
transfer of the bike itself. (no binding)
>> Older enthusiasts will remember BMW staying with Earles style forks for
>> years after the market demanded telescopics - they knew what they were �
>> about. Eventually they were forced by fashion to go to teles.
>
> Don't get me wrong. I love the idea of a link-type front suspension,
> especially what BMW has done with the latest multi-link front end.
>
> But if *you* want to graft a modern motorcycle front suspension onto
> your scooter, you're most probably going to use telescopic struts from
> a mass-produced motorcycle after acquirng the parts from a breaker.
>
Yes, exactly - provided I can find some that can be
reconfigured/shortened.
> I know what it's like to have a machine shop full of lathes and mills
> and grinders, but whatever you produce in your shop is going to be one-
> off and, if you break it, your motorscooter will be out of commission
> until you make a new part.
Certainly. However, the scooter is intended as a testbed for the motor and
as such won't travel very far. My intention is to make it so that it won't
break!