If car tires are merely underinflated, but not flat, how much damage would you get by driving for, say, 500 miles on them?
(this isn’t even worthy of General Questions.)
I guess in part it may depend on just how underinflated they are and how hard you’re driving. They’ll generate more heat which may cause them to soften and have less traction, increasing wear. Also, if you hit a bump and they’re low enough that the wheel rim hits the interior surface of the tire it may cut and that’s never good, depending on the severity.
Less air means more surface contact, which means more friction, which means more heat. Overheated tires can blowout.
But if we’re talking a few PSI underinflated I wouldn’t worry about it for 500 miles.
It’s not so much about friction as it is about sidewall flex. The sidewall flexes every time the tire goes around, and that generates heat in the tire carcass. If pressure is low, the sidewall has to flex more to create a bigger contact patch; more sidewall flex = more heat, and it also means more fatigue. Eventually the combination will be too much, and the result may be tread separation and/or a complete blowout.
The OP’s question is unanswerable because we know nothing of the tires, their amount of underinflation, how much load they were carrying, and how fast he was driving.
I feel like you’re saying exactly what I said except you added that more sidewall flex means more surface contact. As for generating heat, it is absolutely about friction. Sidewall flex alone isn’t going to cause blowout if you don’t drive on it.
The side wall is actively flexing as you’re driving to accommodate the larger contact patch. It’s like this ( at the top and like this c at the bottom. With every revolution the sidewall is bent and stretched back and forth more than it would be if it were properly inflated. That extra flexing is where the extra heat comes from.
If you installed larger tires with the same contact patch as the under inflated tires, would they blow out? They would have the same friction but much less flex than the stock tires.
I’m not here to argue with either of you; it just seems that tires are stress engineered to be operated at a certain inflation. Operating them at a different inflation has to put stress where its not designed to be.
This may be what Both of you are saying.
Personally I find it worth while to keep a gauge in the trunk and to spend the extra $.50 at a gas station to make sure the tires are giving the performance that they are supposed to.
True, parking a car on underinflated tires isn’t particularly problematic. Rather, it is the flexing/unflexing/flexing/unflexing that happens when driving that does it. Each time the sidewall flexes or unflexes, a small amount of heat is generated in the material due to its viscoelastic behavior. After some miles of driving, the tires have gone through many flex cycles and generated a substantial amount of heat. When you say “friction,” this isn’t the same thing; friction implies sliding between the surfaces of two separate materials, whereas viscoelastic losses involve heat generated inside one contiguous mass of material.
Rubber vibration-isolating machine mounts can get hot for the same reason - viscoelastic dissipation - despite the lack of any sliding action that could be regarded as friction.
Here’s a couple of references:
http://www.aa1car.com/library/tirefail.htm
“Tires that are underinflated experience excessive flexing in the sidewalls which causes them to run dangerously hot, especially at highway speeds during hot weather. The buildup of heat can lead to tread separation or a sudden blowout.”
“Without proper air pressure, the internal components of the tire—fabric, steel, rubber, and composites—flex beyond their designed limits. What happens is much like bending a length of wire: Manipulate the metal long and far enough and it will overheat and snap. Try it with an old-style wire clothes hanger. (Warning: The failure point will be skin-burning hot.) Without proper air pressure, the tire’s internal pieces will overflex, weaken, and, eventually, fail.”
this is also why bias-ply tires used to be far more prone to “blow-outs” than modern radial tires are. even properly inflated, the criss-crossed fabric layers would try to twist and scrub against each other and eventually separate and fail.
Modern car tires are (IMO) an engineering marvel, and people don’t tend to realize how much better they are than the stuff we had up through the '70s.