I was wondering about my brakes on long, steep downhills. On a bicycle I would alternate brakes to let them cool. Yesterday I rode down a long steep grade and held the brake on most of the way down. I would say about 15 minutes. I let go on a couple of turns where it eased up a bit. On my ungeared unicycles, I can use my legs as brakes most of the time. When I’m in high gear I don’t feel comfortable without the brake (Magura brakes). The grade was an average 17% grade and I’m using 137 cranks. How much braking is too much?
On a side note, my disc brakes that came on the Oregon are pretty noisy. Not squeaky, just loud. Is this normal? They don’t seem to have the stopping power like the maguras.
When the tyre blows out or the braking power fades.
… you’re welcome …
About the fading, you just have to stop and let the brake cool as soon as this begins to happen.
If you want to measure when the tyre becomes blowout-critical, you must know the pressure inside it, because this and not the temperature per se is what will make the fabric fail at some point.
Maybe you could use a pump with a manometer,
or you could glue a temperature measuring strip to your rim and take the ideal gas law to calculate the temperature that corresponds to your critical pressure (p is a function of T if V=const).
As a critical pressure, you might want to take the max pressure on the tyre. Or less, if think the strength of your rim is the limiting factor - many combinations of tyre and rim widthes out there are critical.
Or more, if you have confidence in your rim and you choose to believe the rumour that Schwalbe tyres are calculated with a safety factor of 1.6 (“max. pressure” plus 60%).
Oh and the tyre must be absolutely properly mounted or the tube might find its way out before the fabric fails.
You know what? With all these things taking influence, you should better have tried that very pressure with your floor pump, while wearing ear protection. I would be very reluctant to trust theory, especially my own version of it.