Chalo wrote: ↑
Jul 12 2018 12:47pm
Greg Herbold, John Tomac, and the other competitors in the then-new sport of MTB downhill racing at the turn of the '90s seemed to do fine with rim brakes. Disc brakes were available to them if they wanted. Shimano's came out in 1975.
And now every single competitor uses discs.
Every. Single. One.
If the the strongest rim brakes really were stronger than the strongest disc brakes, then lots of DH competitors would be using them - because they would win more races. They don't.
You seem to be taking this very personally for some reason. No one is saying that rim brakes suck, or that they don't work. They do. But there are some things that disc brakes are better at - and that's why they have taken over the market.
From a personal perspective, I once blew a tire from overheating during a long descent in Luxembourg. (rear tire fortunately.) By the time I got stopped the rim was almost, but not quite, too hot to touch. The combination of that and a high pressure touring tire managed to pop the bead off the rim and expose the tube.
About ten years ago I was on my MTB doing a long, steep descent in a canyon in San Diego. These were with 160mm discs, which weren't the best choice for such descents. When I got to the bottom I got off my bike for a second and my calf accidentally touched the rear rotor. I instantly got a burn, and for about two weeks had the vent-hole pattern tattooed on my calf.
So the disc was that hot but the tire was fine - because the disc is a long, long way from the tire, and there's very little thermal path between the two. Plus which, of course, the disc was dissipating heat a lot faster, since heat flow depends on the difference between the object and the air. You are better off with a disc that is 50C hotter than ambient vs a rim that is 25C hotter than ambient, at least in terms of heat transfer.
Does this anecdote mean that rim brakes suck and you should never use them? Of course not. I used them for twenty years because they were pretty much all that was available - first cantis, then V-brakes. They work. I've used them for heavy ebikes, and they worked ok. But when I can I replace at least the front with a disc because they just work better for me over a wider range of conditions (wet, dirt, not perfectly true rims.) And there are the minor advantages as well - not as much shimmy when stopping with a less than perfect rim, one less thing to mess with when changing wheels/tires, easy upgrade to larger/better versions.