Road Discs?

Last week I pointed you to Lennard Zinns' Next Big Thing article. Well, he's at it again with round two called More Big Things. This time, he predicts that road discs will become more mainstream, and might even be used in racing. If you've been reading this here blog for any length of time, you know that disc brakes are something I espouse. I've written about them before, including listing the pros and cons.

Lennard makes some interesting points, though. Let's take a look, shall we? One of the arguments that is often used is that the bike has a disc--the rim--that works well for stopping. There are two problems with this. One, you are wearing away at a structural component. Every time you hit the brakes, you remove metal from the rim. If you ride a lot, or know someone that does, chances are that you've seen or experienced a rim failure due to excessive wear of the braking track. Second, as Lennard points out, every time your rim gets wet, you lose braking power. Why is this acceptable? Also, aluminum is a lousy braking surface.

Lennard goes on to say that the biggest drawback is that they are heavy. The calipers are heavy, the rotors are heavy, the hubs weigh more and can't build pretty radially laced wheels and expect them to hold up. All true. However, I think that if they were more widely adopted, there would be a concerted effort to drive the weight down. As it is, road disc brakes are just mountain bike brakes adjusted to work with the leverage ratio of road brake levers. If they were road bike specific many of these arguments could be better addressed.

Lennard suggests that one weigh to reduce the weight is to use a smaller rotor--true--but that, he says, leads to more heat build up--again, true, to a point. One of the nice things about discs is that you can brake later. You don't need to drag your brakes as much, so it is possible that while the heat generated is significant, there is plenty of time to cool them down between uses. He also suggests that using different materials will help. This is true, and it's something that I think we'll see if companies like SRAM and Shimano start making road bike disc brakes, not mountain bike disc brakes adapted for road use. Where Lennard errs, though, is suggesting the use of Carbon-Carbon brakes like those used in Formula 1 racing. While they do work very, very well at elevated temperatures, they don't work well at all at more normal operating temperatures. They need to be heated up to greater than 400 degrees before they start working well. There is no way you'll be able to get a bicycle brake that hot. I've tried. It's really easy to get a car brake that hot, though. That being said, there are ways to dissipate heat--fins on the caliper, different pad materials, different rotor shapes, using MMC (metal matrix composite) rotors to help conduct the heat away from the pads--and if road bikes use smaller rotors this will have to be addressed.

I firmly believe that the advantages outweigh the disadvantages when it comes to disc brakes. Their overwhelming adoption among the off road crowd highlights this. When a disc brake designed from the ground up for road bike use becomes available, I'll be the first in line.