8 or 9.5 on 235/40 @ autocross
 

I currently am running 18x9.5 with 235/40. which gives me a slight stretch for a pretty stiff sidewall, and very responsive turning, I was wondering if I would notice a difference if I mounted these size tires on my stock 18x8. would it be something drastic? the tires would definitely not be stretched on the 18x8 so I am unsure if ill lose performance by going to a smaller wheel width. the tires are Hankook rs3 and this is for autocross.

Honestly, if you ran a blinded test, I doubt most people would be able to tell the difference.

I assume you're in SP, yes? If so, why so little rubber on the road?

I feel like the 235/40 will be plenty meat on the x8. I ran 245/40 last season and it the sidewalls were way to soft for me. The 9.5 wheels were not intended for autocross/track but for the street. Thou after I purchased I wanted to try. Then realized it bumped me out of stx which is why I want to go back to the x8.

Well, 18x9.5 +15 isn't good to start with in the first place...

I didn't start with it, it's my third set of wheels haha, I plan on going more aggressive on my next set.... So my conclusion is x8 is a better option for autocross , thanks

17 x 9's work for STX. Tires are cheaper too.

Most people run 245 or 255 on 8" wheels for autocross on RX8s, but it all comes down to personal preference and what's fastest. 255 (max permitted in STX) on a 9 is the popular setup for STX. Once you burn up your Hankooks you should probably look into the RE71R or Rival S as better replacements.