I have a set of factory reproduction c5 y2k wheels, and I always thought they were 18x10.5 out back and 18x9.5 up front. When I bought the wheels they had 285/40/18 Pirelli P-Zeros out back and 265/35/18 of the same up front. I measured the wheels today and came up with 18x12.5 out back (subtracting 1/2" for the lips would measure an actual width of 12") and 18x9.5 up front. This really surprised me, those 285s must be really stretched which is why they dont look like a 40 series sidewall. I found a deal on some Michellin Pilot Sport 2 335/30/18 for the rear and 275/35/18 up front. I know id need to use a spacer to fit these tires but how big of a spacer? 1/2" or as big as 1"?

 

What's the offset of the wheels? I'm not running a spacer with my deep dish Y2k's (54mm offset), with 335's. I'll probably put a small one on, just to be on the safe side. But, so far, no problems at all.

 

I always thought they were the vette offset because I had to beat the crap out of the fenderwell to fit the rears, but at the time I thought they were only 10.5" so they could be a 54mm offset.

 

Are you measuring from outside to outside?

 

From outside to outside and subtracting .25" for each lip

 

Unless someone widened them, then they're a 10.5" wheel. Take a picture of how you measured them.

Also, there's no way you fit a 12.5" wheel on your car without a spacer, which would cause it to stick like 1.5" out of the wheel well, or a mini-tub.

 

12" wheel, like I said u need to subtract .5" from the overall width when measuring from outside to outside

 

wouldnt it say the size of the rim on the inside of the spokes? every wheel i have does.