[SLO-BOB]

What ypu really want to measure is the tire. In your case, you would drop down the sidewall size to make up for the increase in wheel diameter. There are variables but the basic idea is that if a 911 would start with something like a 185/70/15 tire which has a diameter of "x", ideally you would increase the wheel size but reduce the tire size so that it equals "x" also. Generally speaking if you went up in wheel size by "1" you would drop tire sidewall size and get a 60 series tire. This is sometimes referred to as plus 1. Next step would be 17 inch wheels and 50 series tires=plus 2. Unfortunately this theory doesn't always add up as going to a wider tire, such as 185 to 205 somehow increases the diameter. I haven't figured that one out yet.

Anyway, I'm going to 16 inch wheels and I figure I need to have 50 series tires, 205/50/16 in my case, to keep from rubbing. We'll see if that works. They're going to be mounted tomorrow.