This is for my wrx, right now I'm running 225/45-17 but intend on geting 18's soon my question is how much wider of a tire can I go to beyond the 225/40-18. The reason I ask is because of C&D wrx which they put 17's w/ 235/40-17 which they said kept the same rolling stock diameter. Please help.

 

look on the oem tire on the tire rack under "specs" when you look under tire. I think one of the fields is diameter. You then can compare to any tire you want

 

225/40/18 (25.08 inches dia.) is the closest to 225/45/17 (24.97 inches dia.)...........

255/35/18 (25.02 inches dia.) is the next "widest", yet appropriate, size you should consider.

 

i still got the formula, here we go

for example; 205/55/16

try to do this

( 205 * 55 % * 0.78735 ) + 16

= ( 205 * .55 * 0.78735 ) + 16

= 24.877 is the dia size

 

you can go 285/30-18 if you have the clearance