To cut a long story short..

Old set-up:

Volk CE28N 17" Michelin PS2

F : 7.5 +50 225/45
R : 9.0 +63 255/40

New Set-up:

Advan Racing RS 17" Yokohama Advan V103

F : 7.5 + 48 WANT TO 235/40 (Diameter difference 0.86%, 2mm more sticking out)
R : 8.5 +43 WANT TO 265/35 ( Diameter difference 1.26%, 14mm more sticking out)

1. How bad did I screw up by mis-ordering 8.5 instead of 9 for the rear?
2. Can I fit a 265 on a 8.5 wheel?
3. Is 235/265 overkill or will the grip really improove compared to 22/255 set-up?

Thanks for any help

 

1. You can put a 265 tire on an 8.5" rim. You would get slightly more performance out of a 9" rim but you didn't screw up by order an 8.5.

2. see 1

3. Without some major fender rolling and negative camber you will rub with this setup. Grip will improve, but if you are not breaking your tires loose now going larger is overkill. The added weight of tires will slow you down a bit and the wider front tires will follow more imperfections in the road. Going 235/265 has its advantages in grip but if you don't need more grip there are just as many disadvantages.