Originally Posted by
Road Fan
Back to the beginning:
Just a simpleminded view (I am not a tire expert) is that tires that are run a few dozen psi above rating have casings with excessive stress, which by my simple engineer's logic should lead to a premature failure of some sort. I'm assuming problems of wearout, mainly in the carcass and structure, not so much in big impacts like 4" curb jumping. I have a rear admiral who will physically explain to me the error of my ways, in such a case.
As an engineer I have some clue what other engineers will probably do, and I think there isn't a limit printed without some reason, which the lawyers have agreed to. I don't know enough to predict the nature of such a failure. Certainly tread wear is an obvious point. In cycling we normally mitigate this (if not by dieting and working out harder) by using tires with larger cross-section. The loading of my tandem, which is set up for 700c tires that are not very wide, is pretty high from my naive point of view. Using the Berto chart to estimate a tire pressure to achieve enough ride height to protect the rims under most road conditions, the pressures needed are well in excess of the sidewall pressures.
That looks like a problem.
IMHO you are absolutely correct. I've never run a tire over sidewall pressure. However, if you look into it a little more deeply, you'll find that tire sidewall rating and rim manufacturers' tire/width tables are about the same. Which makes sense. Of course a tire manufacturer won't put on a max pressure rating which might result in a rim failure, a very big deal.
Ignore the Berto chart. You don't need that much pressure. Buy some tires, pump them up, ride them. Get experience. OTOH, it doesn't hurt to use my formula to guess at tire pressures. You'll find tires which seem like they'd work fine, but have much too low a pressure rating. Don't use those. Look at the manufacturer's tables, do some calcs, buy 2 tires.