This thread got me thinking that maybe I might go to a 245 when the current rubber needs replacing (if I am still alive) to improve the protection of my rims. So I went in to the calculator and was surprised to find out that a 245 is 1.2% bigger in Diameter than a 235.

Excuse my naivety, but why is this so. I though an 18' 45 profile was an 18' 45 profile.