Originally Posted by dabac .
Er, aren't you forgetting about the rider?
A 175 lbs road rider on a 15 lbs road bike will be just as hard to stop as a 160 lbs MTBer on a 30 lbs MTB. Looking at what would be needed to bring the bike only to a standstill doesn't make any sense.
Besides, relieving the rim sidewall of its double duty of being both a structural member and a friction surface might bring some rewards. No need to worry about CF rims and hard braking any more for instance.
And what added mass there might be will end up by the hub, where it's far less influential than out by the rim.(where it might be possible to save some.)
Rim brakes, compared with disks, are really awful. The only reason they persist is because of tradition and rules still in the dark ages. I come from racing motorcycles where disk brakes have been used for over forty years. The same things were said when someone got the idea to go from drums to disks for motorcycles: "too heavy, the drums work fine". If you've never experienced the ability of a modern sport motorcycle to accelerate, turn, and stop, you would be shocked. Not only do disks provide far more stopping power with virtually no fade at all, they allow extremely fine control over the amount of braking. Both these things are of great value in getting down a piece of pavement quicker. Those calipers with rubber pads flex, they are inconsistent, the pads heat up straightaway and get grabby, heat is transferred into the rim and then into the tire...they are a lousy way to bring 150-200 lbs of bike and rider to a stop.
The reason some riders think calipers are perfectly adequate is because racing cyclists have adapted to the extreme limitations of rim brakes. If a rider is on a long fast descent, care has to be taken not to overheat the brakes, rims, and tires so the braking is naturally far less aggressive than it could be. The benefits dabac noted above are well-known; when you remove the burden of being a braking surface as well as a rim from the wheel assembly, the wheel can be made much, much lighter. Putting the small rotating mass of the disk close to the hub minimizes the weight effect, thus, the material saved in making the rim is simply relocated to the hub area, where it has less impact on handling. Weight is no issue at all, that part is easy.
The biggest benefit is going to be the ability to brake much later, with much more fine control and most important, confidence and consistency. That results in faster times and winning.
When we look at all the controversy about drugs being used for competition, seems like it would be easier to cut back on the doping and bring the bicycle into the 20th (not the 21st) century.