toolonglegs wrote:human909 wrote:toolonglegs wrote:The biggest scare by far which I seem to see a bit too often is people pumping up their clincher tyres too hard when on holidays in places with proper big hills... It really can kill you on the descents and can't be stressed enough.
Can't be stressed enough? It sounds like you are already stressing it too much.
The rated tyre pressure already have a significant safety margin. Unless you are well already above and beyond the recommend pressure combined with crazy overheated tyres then I don't see any risk. Your tyre needs to be above boiling point for there to be much risk.
I would expect nothing less in a post from you.
I am interpreting from this that TLL has witnessed tyre blow-offs on big descents and is attributing this to pressure. These would almost always be seriously scary at best.
H909 is suggesting that the pressure changes aren't all that great so there is not that big a risk.
I think that there is an area for common ground here. Hot clinchers do blow off, it has been demonstrated often enough, but I don't think it is solely due to pressure. I routinely run over-pressured tyres on my tandem (220kg in race mode) to the tune of 30% or more. It was touched on earlier that the universal gas equation has pressure varying in direct proportion to the temperature in Kelvin. Kelvin has the same unit dimensions as Celcius but room temperature is near enough to 300K. How hot do tyres get? If they got to 600K (seems unlikely) it would only result in doubling the pressure, even 450K would only be an additional 50%.
Cold tyres with excessive pressure are not a problem since tyres are routinely tested to double their nominated pressure without a blow-off, there is something else at play rather than just the pressure. I suspect that the temperature is the key factor here, maybe it affects the slipperyness of the sidewalls or relaxes the bead or both. Perhaps this is enough to lower the blow-off pressure from 250psi to something more attainable like 180psi.
In this scenario if someone had tyres at 120psi and then raised the temperature to 450K, the tyres get to the magic 180psi and Boom. If instead they had lowered their pressures to 100psi got to the same 450K then their tyres would only reach 150psi and they have a wonderful time.
Cheers,
Cameron