Quote:
Originally Posted by zenmaster
I always thought the diameter remained constant, regardless of the aspect ratio / sidewall length.
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No, unfortunately it does not. Plug some in here and check:
http://www.1010tires.com/Tools/Tire-Size-Calculator
The overall diameter increases with every step up in width. For 245->255 the difference is not really going to disturb anything though. Once you get 20 or more away you should see if dropping the aspect ratio brings you closer to the stock diameter.