tyre sizes on WRX STI
 

Hi guys
Some advise please!
2002 Prodrive WRX STI, I've recently been given some new Inovit Redline 7.5" X 18" alloys, and am looking for advise on tyre sizes.
This car's going hill climbing in the production class, so need the 18" alloys, but I'm confused:wonder: on tyre sizes....
TIA
jono

bit more??
 

I'm also looking at some 8" wide alloys, ie 8" X 18". What tyres would I be able to fit without fouling or whatever?
Thanks again