Not really what? Actually 17x8 is probably the optimum size for autocross, since that's big enough for a 245/40R17 which is about as much tire as you can easily fit under a GC. Plus it's lighter than an 8.5" wide wheel.

 

I'd go 17s. They'd probably be lighter and lighter=less unsprung weight.

 

If you go 18" should I run 35's or 40's. I am in a Impreza Wagon and need to stick with 215 size tires.

Most application suggestions say 215x40x18, but a true +2 would be 215x35x18. Is the ride just too crappy on this low of profile?

I too want to keep my unsprung weight on the low side (35's) and not thrilled with a higher rear ratio the 40's will give me. 'Cause I got a N/A OBS and need to stay as light as I can with the 18" applictaion so I can still move forward!!! :-)

 

Your wagon had shorter tires than most other Imprezas. 205/55R16 is the stock size for the RS and for all '02+ Imprezas except STi of course. That's a stock diameter of 24.9", which is slightly more than a 215/40R18 ends up as.

 

Hey thanks. The solution seems to be, because I am using these on a N/A wagon, sensitive to both weight (unsprung sucking up HP) and rear fender clearence, is too run 215x35x18 for a lighter tire (helps with the unsprung weight to keep my acceleration ~ as it were) and also because it is about 3/4 smaller diameter (helps me with a slightly lower gear ratio ~ acceleration) and gives me some 'wiggle room' on the rear fender clearences on the wagon.

It could be the 'princess and the pea'... we will see if my fillings stay in my teeth?