Psamathe wrote: ↑9 Apr 2024, 1:10pm
I have read of concerns with some (poorer design?) hydraulic disk brakes with the brake fluid boiling so I assume some heat must be conducted through the pads.
Just asking the question as I have no idea how impotent different heat dissipation paths might be.
Yes but the brake fluid itself is designed as a heat sink. You'll lose some heat through the rotor itself, some from the pads and backing material, some will go into the fluid. How much that happens depends a lot on riding style, speed, air temperature and the rotor material and backing pad material.
If you're on the brakes constantly, the fluid can boil but you'd really have to be trying quite hard to do that - modern braking systems it's rarely an issue. You'd need a prolonged descent and a heavy rider/bike combination being ridden quite poorly to get close to that on current disc brake systems.
mattheus wrote: ↑9 Apr 2024, 1:51pm
I would *
hypothesize* that rim-brake designs naturally give better air-flow to the hot bits, which would help avoid problems from hot brakes.
If so, that's another reason why 70's tourists in the Alps didn't often complain about brake-fade and the like. And it was rare when the racers first used the same roads, many decades earlier.
I would *
hypothesize* that speeds in the 70's were a lot lower than road bikes of today will do!
That said, I've seen several instances of burst tyres on long Alpine descents when the heat from the rim brake has gone into the aluminium of the rim and blown the tyre. Also used to be a problem on tubulars back in the day cos the heat would melt the glue that held them on. Carbon rims, you can get delamination where the resin bonding within the rim basically melts.
