Hey, this link seems to be the definitive site for tire sizes, etc. I have seen it recommended by many people. However, the specs it gives are quite a bit different than the specs given by the manufacturers on tirerack's website. Specifically, revs per mile. Example-the revs per mile given on the miata site are 757 for the stock 16" size, and 782 from michelin on tirerack. That is a pretty good difference. Should i go by the manufacturer when figuring out the size? I found some sweet 18's with 225-45 18's, and i think they are only off by 2% which is ok. I just want to figure out for sure.