quickest wheel size ?

Which is better for acceleration and top speed, either smaller diameter wheels or larger ones ?

(I'm talking about saloon cars, but i guess it applies to anything)

I also heard that larger wheels put more stress on the driveshaft / transmission etc, is this true ?


thanks
WoodyRacin

I'm not going to say I know a lot on the subject, as I don't, but the larger wheel diameter (and by that I mean the diameter of the outside edge of the tyre) is better for top speed and smaller for acceleration. There is more to it than that, such as the tyre, wheel size, tyre size, sidewall flex, engine power, traction control, etc.

thanks, that it what i suspected.
i meant from the outside of the tyre too.

Your right.

in theory a small diameter wheel will givwe more accel but less top speed and a larger diameter wheel will give more top speed but smaller accel.

But there are a few things you got to take into account.

For a start if you want to adjust accel to top speed you do so by changing gear ratios. Changing wheel diameters come with to many variables.

For a start a larger diameter wheel will give more drag. So you might acctually have a lower top speed from a larger diameter wheel.

If you go for a smaller wheel it will wear faster as ever part of the tyre will touch the ground more times than a larger diameter wheel.

Esentially cars need to get a fine balance in between these 2 variables.

Then there is also stress on the driveshaft etc.

As a larger diameter wheel will need a larger rim it obviously means tat it would be heavier. But I can't see an problems from the teams in strenghtening these parts slightly.

Niall

also.
u get more traction from larger wheels.
more rubber is on the ground at any one time.
can run lower tire pressures to.
also it will change the speedo calibration
and cost more!!

The larger diameter wheel still has the same contact strip but with its lower tyre pressure a lot more of a contact patch is being made.

But lower tyre pressures give rise to lower top speed.

From what I can see its all a matter of balance.

Niall

no the larger wheel has a bigger contact patch with the same pressures.

if u imagine a 10metre wheel..
the contact patch will be larger than if the wheel is 10mm dia.

with the same pressures.

can you see wot i mean?

lower tire pressures will give rise to lower top speed yes. but.
the pressure is taken when the tire is cool.
the lower pressure allows the tire walls to move more as its more squashy.
this heats the tire up (good as they get more sticky)
which makes the pressures higher anyway.

for instance. we start with 16psi, they go upto 24.5psi. and get very warm.

by me saying u can run lower pressures i meant a larger tire is able to support the same weight as the larger tire will be stiffer.

do you lot agree?

I have to agree with Niall that it is a matter of balance. Besides what's already said, there's also a matter of rotational inertia. I agree that a large diam. wheel/tire setup could possibly give you a larger contact patch, but that also put a lot of mass further away from the center of the axle. As more weight is moved away from the center of the axle, it takes more power to rotate those parts. So a 30" rim/tire combo can have large patch, but it would roll like a steamroller.

When I spec tires and wheels for my racecar, I usually pick the smallest size that fits over my brakes because I like to stop, period.

Originally posted by Stealth
When I spec tires and wheels for my racecar, I usually pick the smallest size that fits over my brakes because I like to stop, period.

I'd go along with that. Whenever selecting wheels which aren't limited by homologation requirements, unless going up an inch or two will let me fit bigger brakes and allow me to get a better tyre size than say a 185-60/13 then it's not worth it.

Carlos Fandango super tall racing wheels will require major suspension work to get working properly. There's so many other variables to consider.

Far more effective to play with ratios to alter accel/top speed.

Stacy

I argree with stacy you have to look at the overall picture.
i used to aim for my top speed in top gear on silverstone club straight(quick change where not available to me !) .No good having a 145 mph car that only reaches 110 mph in 4th.(or in my case a D type that never got out of 3rd at Mallory)
Depends on the availabilty of final drive ratios ideally you should use the smallest wheels (less weight,lower,less unsprung weight)and match final drive ratio(dont forget to measure actual distance covered by each wheel revolution).

Originally posted by Brianv
i used to aim for my top speed in top gear on silverstone club straight(quick change where not available to me !) .No good having a 145 mph car that only reaches 110 mph in 4th.(or in my case a D type that never got out of 3rd at Mallory)

Indeed, although I think a better straight to guage top speed on would be the Snett Revett straight. Some people I know are on the limiter in top for a few yards there - just about perfect I'd say.

Haven't yet made that feasible with any of my cars yet though..

Stacy