Quote Originally Posted by racerwannabe View Post
Stargazer, 225/40/18 is the right size. Thats what most people with 18" wheels are running on including myself. Check your calcs again, the diameter should not have increased by 16mm.
Sorry, I'm a bit of a noob with tyres. I used the calc on http://www.carbibles.com/tyre_bible_pg2.html

It calculates the circumference of my 205/55/16 to be 1985.17mm and the circumference of the 225/40/18 to be 2001.82mm, a diff of 16.65mm.

The 245/35/18 only gave a 10mm difference (decrease) in circumference. I did notice this tyre size seems to be less popular - some manufacturers don't seem to even make this size. But I do like the thought of having wider tyres too. My mind is boggling at all these numbers and choices! Will the 245/35/18 fit a 18x7.5 wheel?