How to pick out wheels for an rx8
04-21-2012, 06:02 PM
#28
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.
04-22-2012, 08:23 AM
#31
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.
04-22-2012, 05:14 PM
#34
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.
04-22-2012, 05:19 PM
#35
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.
04-22-2012, 07:42 PM
#37
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.
05-03-2012, 06:43 PM
#39
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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.
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.
05-03-2012, 08:17 PM
#42
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.
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"
Last edited by JCrane82; 05-03-2012 at 08:28 PM. Reason: typos
05-05-2012, 10:58 AM
#44
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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.
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.
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
Last edited by ukrman; 05-05-2012 at 11:04 AM.
