While R&C is in nerd mode here with Mike's handling, I figured I would bring up a topic that has been on my mind for quite sometime...tire theory. If this has already been discussed on THIS forum ad nauseum, then I'd like to continue that discussion, otherwise, I feel that tire theory is NOT independent of the car as it relates to the entire race car package. What I mean by this is simply that wide tires might work better for some cars and not so well for others. In my research, I have come across many articles written by reputable sources and no prevelant answers have emerged. So, as S2000's "gurus", what do we think of the question: With respect to the S2000, is a wider wheel/tire combo better than narrow one? In particular, I'd like to hear comments on the advantages and disadvantages of the most prevelant wheel/tire combonations - 18x10/285, 17x9/275, 16x8/245

My thoughts so far in easy to read pro/con format:

Wider
Pros
*Increased lateral stability due to better camber change resistance
*Marginally bigger contact patch due to a resistance to deform under excessive loading
*Less rolling resistance due to shape of contact patch running perpendicular to direction of movement, rather than parallel (not fully convinced on this yet)
Cons
*Higher unsprung weight resulting in decreased braking and accerlation

Narrower
Pros
*Opposite of wider
Cons
*Lower unsprung weight resulting in increased braking and accerlation

My argument is that given all the pros and cons of each setup, for the S2000, the narrower 16" setup would give better results than the wider 17" and 18" setups.
One of the better threads out there on the subject... http://www.eng-tips.com/viewthread.c...=102250&page=1

 

Tires = black magic. I'm not touching that one

I would be interested in hearing from people that have had experience on different width tires of similiar treads and compounds though. I'll be focusing on AS autocross this year. I'm planning to run 225/245 (with Saner bar and Koni yellows). So far, the f/b ratio seems pretty good, giving me traction on turn-in and corner exit. Anyone know if going wider will help any?

 

I just went with the 225/245 F/B on the stock rims, it seems to work a little better

 

Good to know (when I said I was planning on 225/245 I meant that's what I already have on there )

 

Wow, here's a thread from my local region forum. Pretty interesting stuff.

http://soloatlanta.com/forum/index.php?showtopic=2545

 

Interesting, but they all have different cars, with different suspensions, engine outputs, and gearing, all of which I believe play very big parts in the points of diminishing return along the tire/wheel spectrum.

The genesis of my thoughts on this come from the aformentioned popular wheel/tire combos. It seems as if way too many people are running the 17x9/275/245 setup without an honest consideration of the benefits of the lighter, albiet narrower, 16x8/245/225 setup. Would those with empirical evidence please step forward? If your answer is, "my lap times improved with the 17 inch setup", then can you please elaborate on the handling differences. Or even better, post up your data logs

Matt - Did you convince yourself of the same contact patch size riddle yet? If not, I can draw a picture

 

C'mon. That's "lawyer talk", not "engineer talk"

 

Yes, as I understand it, the contact patch is the same but the wider tire gives more grip due to the fact that the leading edge of the contact patch is where most of the grip is born. The trailing edge is in slip.

Wider is better.

 

In switching from 225/245 16" to 275 on 18" I picked up .25G in cornering. That being said, with the car completely stock, I didn't pick up a huge laptime decrease with it. Only when I started lightening the car and added HP did the laptimes really decrease. I suspect the heavy Toyo's and big rims were too much to carry down the straights. When I did lighten the car though, the big tires were 3-4 seconds faster than the 16".

Does that answer your question?

 

Wider is better for a long list of reasons. The contact patch is not the same -- you typically run lower pressures with wider tires. Also, it's not always the case that larger-diameter-wheel combos weigh more than smaller-diameter-wheel combos. With lightweight wheels, the pounds-per-inch of the wheel can be lower than the same space filled with a tire.

On top of that, you can sometimes get lower overall tire diameters when you switch to larger diameter wheels.

There are very few good arguments for taller sidewalls and narrower tires.