Originally Posted by MrHarris
I've been wondering about this for a long time.
Let's say there's a tire that's 265mm with an aspect ratio of 35 and a sidewall size of 3.7 inches, and a 305mm tire with aspect ratio of 30 with the same sidewall size of 3.7 inches.
Would the 305/30 tire be less comfortable even though both have the exact same sidewall size?
Those two sizes can't have the exact same size sidewall. A 265/35 would have a sidewall about .5cm (5mm) taller than a 305/30, so if you're going by numbers on a website, they're either rounded off or inaccrute. But I suppose they're close enough to pose your question. Given the same brand and model tire in both sizes, there would be very little noticable difference. If anything, the 265/35 might feel more forgiving over bumps, but I think you would only notice it if you had a very firm aftermarket suspension. Assuming the sizes in question are what you're planning on running front/rear, Tte difference in sidewall and overall circumference wouldn't even make a huge difference in RPM (rotations per mile). If anything, you want the rear tire to be taller since they tend to wear out faster. That would give then fewer RPMs. That's what BMW did with the stock fitments. The front 245/40/18s are subject to more RPMs than the rear 265/40/18s, thus sort of equalizing the wear timeframes (unless you do a lot of burnouts