[crashbunny]

i don't know if braking performance is the main reason for disk brakes.

I suspect the biggest benefit is bike makers get to sell new bikes to people who don't need new bikes.

For professional riders who don't buy their own bikes, it's probably more about areo, and maybe weight, as the rims don't need a braking surface. They have more creativity with the shape and material. They only brake for emergencies and going into a corner on a downhill. A tiny fraction of a stage. The areo benefit is for the full length of the stage.

I don't know much about physics but even if the weight of the disks is more than rims brakes, the weight being closer to the centre of the wheel might be a benefit. I suspect in terms of performance, aero is the biggest benefit, though.

even the 12 speed cassettes, from what I've read, accelerating smoothly isn't the main point. for a professional rider, they spend a lot more time at the same speed than they do accelerating. so being able to dial in the perfect gear for the speed, wind and gradient is more important than being able to accelerate smoothly.

[ubermonkey]

Aero matters a lot, even for enthusiastic amateurs. You're spot on about wheel shape being more flexible with disc brakes vs. rim. Materials matter here, too -- early carbon wheels were crap at stopping vs alloy because the rim brake tracks were iffy on the carbon, and if you let them get too hot on a descent you'd ruin the wheel. But carbon wheels are an ENORMOUS upgrade over alloy in terms of weight, and in terms of aerodynamics, so the desire for carbon helped fuel the shift to disc braking.

Discs are also absolutely better at stopping the bike, especially if it's hilly and SUPER especially if it's wet (or muddy, which is why off road bikes took to disc first).

Even in a flat place like Houston where we never would've gone to disc in the absence of market forces, we all realized quickly how much nicer they were. It's a definite upgrade.

You're also right about the cassette. More cogs mean we can have a wider range AND preserve the small steps between them, which is great for finding the right cadence in a paceline just as it is for accelerating.

[kjkjadksj]

Aero doesn’t really matter until you are riding at like 25+ mph. Internal cables are like a couple watt reduction at high speeds. Sure it matters for pros when a race is determined by seconds or less and that makes or breaks your career. For commuters and people riding for fitness though? Absolutely not. If you are riding for fitness wouldn’t you actually want a bike with more drag like all those people running with weighted vests and parachutes?

[kjkjadksj]

You gain different rim designs sure. But you also lose out on fork innovation as the disk side of the fork is now particularly strengthened. I wouldn’t be surprised if there are some pro rider who would still ride rims if their sponsors allowed for it.