Quote:
Originally Posted by nikitopo
I measured once a 205 tire on a 6.5" rim and another on a 7" rim. The rubber on the ground is more with the bigger rim. The 225 tire will give a bit more rubber, but less than 3/4+".
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Of course the same size tire has slightly more contact with a wider rim. I'm keeping the same size rim width as stock, so the contact patch is 20mm (.79") wider with the 225s. And that's not even accounting for variation in contact patch size going from one make/model tire to another, which has considerably more variation than just the theoretical numbers. Again, look through TireRack's specs for the various tires and sizes and it'll show you measured section width on a specified width rim, as well as the contact patch size for that particular model tire. Using my RT615K+ tires as an example, my 225/50 has 8" of contact when mounted on a 7" rim. 205/55-16 doesn't even exist with that model, so going to a 215/45-17 to compare, it only has 7.5" of contact on the same width rim. Theoretical numbers are just that - theory. Reality differs, sometimes significantly.