The correct answer is: It shouldn't when comparing TREADWIDTH of same manufacturer. The section width may be a hair different due to the sidewall height. The shorter sidewall height will have to make a shorter radius curve from tread to rim surface than the taller sidewall height. That means usually, the shorter tire will bulge slightly more on a narrow rim. It all depends at that point, on rim width to treadwith ratio. If you compare from different manufacturers, that is comparing apples to oranges. Not only that, catalogs can have wrong stats quoted.