Since I posted this question, I found this on the PCA website. One guy says no and one guys says it won't hurt anything, go ahead...
PCA Q and A on 18 inch rims on a 1997 Boxster
I still have some general questions about rim sizes, offset requirements, and bolt patterns as well as tire sizes for my car's aftermarket rims. Anyone willing to educate me on these things?
Tire question: My 17's are aftermarket ROH rims (Australian rims designed for domestic cars for the most part). They are 17 x 7 in the front and 17 x 9.5 in the back if I'm not mistaken (I'm quoting this from memory, not staring at my wheels right now).
I last put 225/45's on the front and 255/40's on the back. The front tires are cupping at 10k and worn in the middle of the tire (always kept at 29 psi). Could a wrong tire size be the cause of this problem?
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