225/45/17 on 8" rim vs 245/40/17 on 9" rim
 

Just bought an FR-S and have been researching a bit - thinking of going to 245/40/17's (square) on 9" wide rims, but worried about 'too much' tire messing with the balance and response of the car (vs a good set of 225's on an 8" rim). More grip is great but I don't want to sacrifice dynamics if 245 is too much tire. P.S. car is lowered on RCE springs, will be a driver + occasional DE events for fun. Can anyone comment on these two setups? Thanks in advance.

Suggest you look at Robispec Time Attack Build in Tracking / Autocross / HPDE. He goes faster on the lighter tire, sizes he as tested are in pane #1.

Good luck.
Drive fast and take chances.
Tom

If you don't mind the stock wheels, just get a new set of 225's for the stock rim.

Thanks guys - the Robispec build thread was particularly informative. Maybe I'll just stick with the stock rims and 225 45's for now.

Not a bad choice and get some plastic dip to give the stock rim an aftermarket look. This is my plan for a year or 2.