is wider in back, or equal all around better?

[deezlins]

For handling purposes, would having say 17x8 (235's) front, and 17x9 (255's) rear, or 17x8 (235) all around be better, or would it really make that much of a difference either way?

[Q45tech]

Wider rear tires are used to increase the sideways stickson of a tire ----more probabilty that some rubber will grab hold to reduce fishtailing.

Also to provide more cooling surface area during the time the instant tread patch is not in contact with the road.........a better approach is a larger diameter tire if it fits.......usually not so wider is the only answer.

Remember the contact patch [area in square units] is just a function of inflation pressure and weight on tire......wider tires have wider but less length in the patch shape.

[chmercer]

q45, could you explain why gt500 cars run such huge wheel and tire sizes? i believe the pitwork z uses 18x13 wheels with 330 wide tires on all 4 corners? granted some of this is mandated by class restriction and such, but there has to be some reason for it aside from that.

[grip_racer]

my guess that it would have to do with the downforce generated by the cars. the extra weight on the tires from the air pressure probably widens out the contact patch to the proper size.

im guessing here.

[Nismo_Freak]

q45, could you explain why gt500 cars run such huge wheel and tire sizes? i believe the pitwork z uses 18x13 wheels with 330 wide tires on all 4 corners? granted some of this is mandated by class restriction and such, but there has to be some reason for it aside from that.

He explained it in the thread above.

1. Wider geometry in the contact patch resulting in more traction laterally

2. Big tire = big surface volume which leads to a more consistant and cooler surface

3. Tall tires like the ones used on the GT cars have some give to them so the tire itself will form a better contact patch under post apex acceleration.

4. They run 18's because they use absolutely huge steel brakes (carbon/ceramic brakes not allowed in JGTC)

5. High load index will benefit them a more linear grip progression

Dunno, he might add some more stuff but this is what I know.

[chmercer]

hmm so the clown sized front tires is just to cut down on understeer? only reason?

[Nismo_Freak]

hmm so the clown sized front tires is just to cut down on understeer? only reason?

No, it's mainly there to allow maximum consistency in the tire as it wears in relation to heat.

Read what I posted and think about each one and it's benefit to a full on race car.

[Exar-Kun]

Its also a balanced chassis, so split setups for load shift, etc aren't necessary, its usually been tuned for. So the need to "band-aide" a handling problem with odd inflation and tire sizes don't exist..*ahem*

also, the higher load index and special sidewall contruction allows low inflation pressures (cold), increasing the contact patch further.

bleh.I'm tired and sunburned.

[Q45tech]

Just remember the AREA of the contact patch is ALWAYS the same, only the shape changes as the tire heats up and internal pressure increases.

900 pounds at 25 psi = 36 square inches900 pounds on the tire with 30 psi= 33.3 square inches

900 pounds at 40 psi = 22.5 square inches.........more or less [within 2%]

[Exar-Kun]

Just remember the AREA of the contact patch is ALWAYS the same, only the shape changes as the tire heats up and internal pressure increases.

900 pounds at 25 psi = 36 square inches900 pounds on the tire with 30 psi= 33.3 square inches

900 pounds at 40 psi = 22.5 square inches.........more or less [within 2%]

*continues to beat dead horse with stick*Man, oh man...I love it when i get backup on my points.Thanks Dennis!