This thread showed me that I'm a stupid face

 

It's not cool to do smart things anymore

 

Mr J , you say you dont need anything wider then 245 tires unless FI. What if you get ultra super duper light weight wheels and super duper light weight tires ?? Wont performance be better cause youre getting better/more grip but with less rotational weight.

 

In fantasyland

 

I feel like fantasizing right now...yes, right now. Will let you know the outcome...lol

 

It isn't just the weight you need to be concerned with. Frontal area of the tires will increase drag on the straights, lowering your top speed. Larger than 245s work great for autocross and shorter tracks though. J is right though, 265 are pretty much a waste on the street.

 

That being said, I got some sticky 265s to put on and I have no intent to autox. I break my own rules.

 

Yeah, I hear you. I also have 265s, and I only autocross a few times a year. 265s sure look good in the 8 though. Check out my album pics.

 

A 265 Hankook RS3 or the like on a 9.5 or 10 inch rim with a high offset light wheel (RPF1 etc.) probably would really make a difference over a 245 in terms of high speed cornering but, I am just guessing, the autox guys would know better. I know my 285's had more grip than my 245's.

 

Yea but the thing is you give up a lot more in straight line performance due to increased friction and rotational mass (or whatever the term is). If you had 500whp then it would be a different story because you could use the grip in all situations.

 

makes sense.

 

The drag from the tires is always there, regardless of your horsepower numbers.

Rotational mass or inertia is the correct term. Newton's first law of motion.

265/35R18 tires are usually about 1 pound heavier than 245/40R18's of the same model. This of course is just a generalization based on the weights listed on Tire Rack.

 

I'll try to add some pictures later today of common setups.

 

Good info, here are my 2 cents.

Point 1 - Tires are made of deformable rubber and will give the most grip when at the correct temperature. If the temperature is too low, you won’t have any grip, and if it gets too high then you’ll ruin the rubber. So, wider tires with low sidewall will dissipate heat better then narrow tires with high sidewall.

Point 2 - Thinking that wider tire gives you more grip is not always true. Contact patch stays about the same with narrower vs. wider tire as long as the load and tire pressure do not change. As you increase the width of the contact patch, the length of it decreases. Depending on the sidewall stiffness, wider tire may give less grip then narrow tire. So to compensate, as the tire gets wider, you would need to “deflate” the tire to make sure contact patch gets bigger.

Also as someone pointed out earlier, wider tires will decrease liner acceleration but will be better for lateral acceleration.

So, wider tires do not always give better traction, depends on a car, situation, and conditions.

 

The first half of point 2 I don't really understand. Same load/air pressure on different width tires results in the same contact patch? If the tire were 2 feet wide it would only have like a 1/4" x 2ft contact patch?

 

I sort of see what you are talking about but I can't see it being that big of a change.

 

You are correct that tires will provide the most grip when working in their optimum operating temperature. This is different for every tire model, and if you are serious about track performance you will know what your tire's optimum working range is and setup your car for conditions to meet that range. Wider tires are not always better than narrower tires if you can't get the wider tires up to proper temp (lightweight car, cold conditions, slippery track surfaces, etc...).

Not sure where you are getting the idea that tires with lower sidewalls will dissipate heat better than narrow sidewalls. The specific heat of the rubber does not change between different sizes. Now I will say that tire profile is related to heat generation in the tire, but it doesn't relate to heat dissipation.


Exactly. The thing that people have a hard time understanding is that proper setup is never black and white. There are very few universal generalities that you can apply accross the board. 99% of the time the correct answer is..."It depends"

 

Good thread J. +1 sticky nomination

Someone needs to start another thread "How to pick out dysfunctional wheels for a RX8."

 

Basically. Wider/shorter contact patch is better for cornering (F1 tires), and narrower/longer is better for straight line acceleration (drag racing).





Also, even if the contact patch is increased by significantly increasing tire width, the “grip” again will not improve significantly. The reason is, as you increase the surface area of the tire, the weight pushing down on a rubber particle decreases. As you increase the surface area touching the ground, the rubber/glue particles break contact with the road and hover over the road instead of touching because there is less force pushing on every rubber particle. So ultimately the amount of rubber molecules making contact with the road particles are not increased when you use a larger or wider tire on a vehicle with the same weight.


I agree that the specific heat does not change signifinactly, but heat dissipation will change depending on the shape of the tire. Wider tire will dissipate heat better then narrower tire due to larger surface area with the “outside”. That’s one of the main reasons why race cars have wide tires (not for “grip”). Another variable affecting heat dissipation is rubber compound. Tire speed ratings is the speed at which the tire is designed to maintain proper dissipation of friction generated heat. Some examples, H-Rated is up to 130 MPH the tire can resist temperature buildup, which in turn avoid overheating of the tires which causes failure. Z rated is 149+. Some people mistakenly believe that a Z rated tire has more traction than an H. This is not always true as the rating is based solely on heat dissipation.

Wide tires (the good)
- Look great
- Slightly better in extreme cornering

Wide Tires (the bad) - causing worse fuel economy, slower acceleration
- More rolling mass
- More unsprung weight
- More aero drag
- More expansive

 

I now take back my previous statements.

On the edit/rewrite.

 

Bump

 

i broke rule #12 sorry jonathon lol

 

bump

 

awesome thread !!!!


thanks for the precise explanation

 

just read whole thread and all i gotta say is BUMP
"THE MORE YOU KNOW"