Originally Posted by 808MGuy
There's also another component here that is not being taken into consideration. While you are comparing overall height there's been no talk about the width and how it affects clearance from the fender and the rear suspension. At 305/30, you might be near stock in terms of overall diameter but you are much wider than stock and depending on the offset of the wheel you could be rubbing the rear suspension components. I don't think I've seen anyone running 305/30 yet and this could be the reason why.
True, but I was trying to address the OP's concern, which was about comfort. Comfort is more affected by sidewall measurement than the width, although more width can cause wandering (tendency follow ruts and shy away from crowns). Plus, I don't think the OP is talking about running a 305/30 tire on the OEM rear wheel, at least I hope not.