Very good information in this thread. Keep in mind that in most of this information be presenting it is in terms of "optimization" not "diminished results".
Example:
A: I have a 225/45/15 tire so running a 15x8 or even a 15x9 will improve the way that tire performs vs running a 15x7 wheel.
B: I have a 15x7 wheel. If I increase the size from 195 to 225 will I see a improvement in cornering forces.
Both A and B are correct
and A does not cancel B. Just because it's
optimal to run a 8 or 9" wheel with my 225's does not mean that the 225's on my 15x7 won't be an improvement over my 195's or 205's. I personally have racing data that backs up this point.
It makes sense to use a wheel width that is within spec of tire manufacturers recommended width. Example:
Hankook Ventus RS3 in 225/45/15 Recommends a 7"-8.5" wheel.
http://www.tirerack.com/tires/tires....num=245WR5Z222
If you look at that chart for that tire, Hankook doesn't recommend a 9" wheel until you reach a tire with a section width greater than 10". Interdasting! (255/40/17)
So running "over-tired" is not going to decrease performance
until you reach the point of diminishing return: Tire breaks the bead, Tire can't actually be mounted, not all the contact patch is being utilized, engine isn't strong enough to turn those big heavy tires etc etc etc. Conversely running tires wider than your wheels is WAY better then running tires skinnier than your wheels. Just say no to Hella Flush.
Here's a picture of the 225/45/15 Toyo RA1 on my 15x7 wheels. As you can see they aren't exactly "struggling" on those wheels. (only pic I had of tire mounted on my wheels) BTW: that dent is thanks to a Spec Miata.
I love testing tires. In 2011 I raced on Toyos, Goodyears, Hoosiers and Hankooks. This year just Hoosier and Hankook but next year I'm looking forward to the new Toyo RR.
Tires as of mid season last year: (and those were just the Toyos!)
