Originally Posted by
pdlamb
So, you've never heard of a chemical engineer being called a Chem E;
I’ve never heard of a chemical engineer being called a ChemE nor of a group of them being called ChemEs. I’ve heard of them being called a chem. e. (with or without the punctuation). You were unclear in your useage.
That said, I am familiar with what “live steam” is and its uses. I don’t know of anyone who would call steam rising off a hot surface as “live steam” nor just boiling water as live steam. That designation is more for a boiler under pressure.
you missed the part about going through a ford, which let water get into the rim;
Nope. Didn’t miss it. Just don’t believe it. Water that hits a surface that would be at (or above) the boiling point of water isn’t going to allow water to get into the rim. The water hitting a metal surface that hot would be subjected to the Leidenfrost effect which is the same as water dropped onto a hot pan. It creates a layer of vapor under the water and the water is held away from the surface. If the rim is cool enough for the water to get into the rim, the rim is too cold to make “live steam”.
you're conflating dynamic heat transfer (heat going through the rim from the brake surface) with equilibrium thermodynamics;
Nope. Not at all. I’m taking dynamic heat transfer into account. Yes, heat would go into the rim from the friction pads rubbing on the side of the rim. But the heated portion of the wheel would have to travel a long way through air that is actively transferring heat
away from the rim. The rim isn’t a small piece of metal and has significant surface area for radiating heat away. By the time the part of the rim that is heated at the friction point to reach the bottom of the wheel where it would be in contact with the water, the rim would have cooled significantly. Contact with the water would cool it even further as boiling…or even just heating…water is endothermic. It sucks heat away from the metal very quickly and cools the metal rapidly below the boiling point.
and you've never overheated a bike wheel on a downhill;
Correct. Because I know
how to use my brakes from years of using them on many, many, many steep downhills.
and you don't mention ever seeing or hearing about an overheated rim leading to a tire blowout.
Nope. Never heard of someone doing it nor have I experienced it. I’ve heard myths about how it “could” happen but I’ve never met someone to whom it has really happened. As I stated above, the increase in pressure due to temperature is actually quite a lot lower than most people think it is. Using the 1 PSI increase for each 10°F increase in temperature, going from 70°F to 212°F would only result in about a 14 psi increase in pressure. As long as you aren’t using something silly like a hookless tire, a 14 psi increase isn’t likely to cause a tire to blow off the rim at the rated pressure.
Remind me why I should consider your opinion on how hot a bike tube can get "informed?"
Because I know a lot of stuff.
Going back to
staehpj1‘s initial question, while the TPU material softens at around 80°C (185°F), it doesn’t melt until about 140°C. Soften doesn’t mean that it would be close to failure nor would it be close to tire blowoff. Melting would probably be bad but, for the metrically challenged, 140°C is about 285°F. That’s a whole different temperature and would be even harder to attain through braking.
And, to be clear, I probably wouldn’t use a TPU tube. They are too expensive and still a bit of a pain to patch.