89mulletbird

iTrader: (4)

Alot of supercars use a larger diameter rim in the back. From what I've gathered, it's for a larger contact patch. Anyone got pics of a thirdgen with a larger diameter wheel on the back? I'm thinking of going from 17" to 18" in back just because there is more tires available in 18".

Base91

iTrader: (1)

I think maybe a part of that is so the sidewall height looks the same. Depends if you want/need to swap wheels/tires back to front and how the car handles. Also how low profile you want to go. Remember the diameter needs to be close without other issues. I've got 40 profile on 17 inch wheels and wouldn't want less on the roads where I live.

paul_huryk

The diameter of the wheel has nothing to do with the contact patch - diameter of the tire is what matters.

Keep in mind that most exotics are either mid or rear engined and their weight bias makes the staggered front to rear sizes very useful. GM used staggered sizes on the C5 Corvette back in the 97 model (17"/18"), but went to 18" all around for the Z06 - a car that is an extremely good handler.

There is no shortage of tire choices in either 245-45-17 or 275-40-17 at this point, although there are just as many choices in the 275-35-18 or 275-40-18 sizes too. Once you get wider than a 285, there are much more choices in 18" tires honestly. So don't base your decision on a perception of availability.

Keep in mind that if say you run C5 vette wheels & spacers on your car with a 245-45-17 in front and a 275-40-18 in back the car is going to over steer like crazy. This is due to over 55% of the weight bias being on the front tires and having a lot more tire (and grip in the rear). I always recommend a 275 tire in front and a 275 or wider tire in the rear, exception being a really precise 18" fitment with 295 tires all around. a 275-40-18 will also lower your effective gear ratio by 4% due to being 1" taller.

89mulletbird

iTrader: (4)

Hi Paul - I currently have 17x9.5 in front with 275s, and 17x11 in rear with 315s.

The problem is I don't have enough backspacing in the rear and my tires are sticking out of the fender wells. I'd like to buy some new rear rims (Torq thrust) with more backspacing, but I'm deciding what size I should get, what would you recommend to complement my front 275 tires? I plan on tracking this car, thanks.

scholtmj

iTrader: (3)

C5 Z06 has 17's up front. 265/40-17s to be specific.

paul_huryk

My bad...

265-40-17 while a nice size, is an oddball with few tires available compared to the 275-40-17 size.

scholtmj

iTrader: (3)

18s all around look much better on that car IMHO.

paul_huryk

275 fits all the way around with the right BS, no problem.

The two issues with the 315 in the rear is the fit and also availability. The 315 only has 5 or 6 tire choices these days, making a matching set really difficult. While I'm all for max tire under the car, I have had nothing but positive feedback on my wheel customers switching from a 245-50-16 sized tire to a 275-40-17 one. Some racers picked up multiple seconds on the same race courses with the wider rubber. I'm sure a 315 in back would help, but have no data to support that guess.