Tire Width?

[renfield90]

Originally Posted by robispec

Time attack or fastest lap has different requirements..from road racing. Wider doesnt have any more grip/surface/psi pressure. area what it does have is the ability to spread/manage heat. Thats why for one fast lap as long as you dont overheat the tire in one lap SMALLER IS FASTER.
That being said this chassis "uses" tires better than almost any chassis I have worked on.

Maybe I'm misunderstanding you, but geometry and physics say you're wrong - a wider tire has more surface area, and assuming the coefficient of friction remains the same, will generate more grip at optimal operating temperature.

What you say is absolutely true for a competition where you have maybe one warm up lap - the skinnier tire will be in its happy place and the wider tire...not so much. What I would then suggest is a wide tire with a softer tire compound (i.e. with a lower operating temperature range). Depending on tire rules for your series, this may be difficult or even impossible to accomplish.

[robispec]

more surface area = lower presure/area = lower friction at = coefficient of friction.
and the coefficient of friction term is also dimentionless when solved for...Ever wonder how a good bicycle racer going downhill in the tight twisty mountain roads on LESS THAN TWO SQUARE INCHES of contact patch can pull away from the motorcycles and other suport vehicles? Paul Handley "the racing and high performance tire" explains this fact in great detail...area controls heat it is the only method to do this. Heat builds up over time...

[track_warrior]

Im running 245 RS3's on a set of wheels and 225 BF goodrich R comps on another set. I would not go wider than 235 for a bolton on car.

[CSG Mike]

Originally Posted by renfield90

Maybe I'm misunderstanding you, but geometry and physics say you're wrong - a wider tire has more surface area, and assuming the coefficient of friction remains the same, will generate more grip at optimal operating temperature.

What you say is absolutely true for a competition where you have maybe one warm up lap - the skinnier tire will be in its happy place and the wider tire...not so much. What I would then suggest is a wide tire with a softer tire compound (i.e. with a lower operating temperature range). Depending on tire rules for your series, this may be difficult or even impossible to accomplish.

It's all about finding the right balance for the fastest lap time, and right now, that balance happens to be at a relatively skinny tire.

[ayau]

Originally Posted by CSG Mike

It's all about finding the right balance for the fastest lap time, and right now, that balance happens to be at a relatively skinny tire.

Have you guys tested 215 street tires on 17x8 rims? I'm curious if going down one more size will decrease your lap times even more.

[CSG Mike]

Originally Posted by ayau

Have you guys tested 215 street tires on 17x8 rims? I'm curious if going down one more size will decrease your lap times even more.

Yup.

We've been juggling 215, 225, and 235 tires lately.

[robispec]

Im Trying 205 Stickies this weekend...

[CSG Mike]

Originally Posted by robispec

Im Trying 205 Stickies this weekend...

Sat or Sun? I may be there for the other class we discussed

[robispec]

Both days instructing.

[robispec]

both days!

[CSG Mike]

gahhhhhh okay.

[rx3]

If the friction coefficient was constant, a 165 wide tire would have the same grip as a 345 wide tire. But the friction coefficient is obviously dependent on the surface pressure (weight of the car divided by the contact patch) and the temperature reached with that surface pressure. (And anything below or above the optimal temperature reduces the friction coefficient.)

At the Autocrosses I participate almost all people in my class run on narrower tires than I (235) (mostly Honda Integra DC2 and Renault Clio RS/Sport).
All races this year have been pretty cold and even wet and they were all won by people on DC2's on just 205 and 195 wide tires. People here run on Toyo R888 or Yokohama A048 (street tire class). I think that these type of tires need possibly more surface pressure in order to obtain enough heat (than the ones people typically use in the US or maybe people racing in the US are simply exposed to much warmer weather).

Also, I talked to a guy with a Celica GT-Four who won in his class and he ran on 225 wide tires with a tire pressure of only 27 psi (cold).

[Scooby South]

As a autocrosser...and As per the rules for my class, I am allowed a 9 in wheel as well as a tire width up to a 265. I have both 245 and 255 on two different sets of wheels. There are a number official reasons that we choose those sizes...weight, grip, performance and gearing...since most of our stuff is in 2nd gear. So we look for a tire size that will help with that. Additionally, we want fhe widest tire so it has the most lateral grip, so in the case of autocross, the heavy transitions on a wider tire help with heat management...as a thinner tire will heat up more, loosing valuable grip..this is the autocrosser perspective. I don't find that I lose feeling at all, matter of fact its enhanced. This is for a nationally campaigned car in STX.

Bill

[rx3]

That's a good point. Maybe because Autocrosses (in the US) are usually mostly driven in 2nd gear (more torque) and since there are more turns/time, tires are getting hotter and wider tires are an advantage.