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CX Disc Impressions After a Year

Last October I started racing 'cross and bought a bike with the up-and-coming disc brakes (Avid BB7 on Van Dessel Gin & Trombones). I've ridden about a dozen races now and also did a bunch of trail riding between January and September.

There are several CONS that other reviews don't usually mention:

* Tight tolerance. There's only about 1 mm on either side of the rotor between the pads. In muddy or sandy races, I hear it grinding after one warmup lap.

* Screeching. The front brake almost always makes noise no matter how recently I've cleaned it. I'm using sintered pads but plan to try organic this week.

* Rotor rub. With the strict tolerance between rotor and pad, any bend in the rotor is instantly heard every time the wheel turns around.

* One way grab. On BB7 calipers, depressing the brake lever moves only the outer pad. My Shimano XT brakes on my MTB both move, which I feel gives flexibility for greater tolerance and keeps the rotor true.

* Too much power. The 160mm rotor in the back is too strong for the width of a CX tire. I frequently skid on pavement, dirt, and gravel. (Maybe this is a good thing?) In most races, the front brake is more useful anyway.

* Full cable. Installation directions recommend running cable housing the full length of the cable. But the frame isn't really made for that, so I have a floppy length of cable running across the top of the bike, held in with zip ties. Given the strength of the back brake, I think I can afford to ignore Avid's advice and run it open on the top tube (even if it makes rear braking less powerful).

I've never had problems stopping with disc brakes. But the noise, maintenance, and tight tolerances make me question whether I should abandon disc brakes until better calipers are designed.

The Gin & Trombones is easily converted back to cantilevers, so I might try them for comparison.

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Permalink Reply by Adam_Mac on October 15, 2012 at 4:10pm

Great insights here. I have also enjoyed reading this article:

http://www.cyclingnews.com/features/tech-cyclo-cross-disc-bike-roun...

I am all for tinkering, but not ready for what disc takes for the 15-20 races this year with a dedicated race bike

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Permalink Reply by Geoffrey Grosenbach on October 27, 2012 at 1:29pm

I've decided to give up on disc brakes and retrofit my bike, probably with mini-v rim brakes.

Today's MFG race in Seattle was wet and pretty muddy (first real mud of the year). On the first lap I heard grit grinding around the rotor. I had no problem stopping, but afterward my back rotor was making a horrible noise. The spring that holds the disc in place had come loose and dragged itself across the pad. There's a deep gouge in the pad, going all the way through to the back in some places.

This happened last year but I thought it was my poor mechanical skills that caused it. But these pads had been fine for several races until today.

Disc brakes are supposed to be great in mud, but I've found that they are too sensitive to malfunctions like this when it's dirty. I'd rather deal with more straightforward issues of mini-v brakes instead of the constant screeching and sensitive tolerances.

The only problem is that I had started building some disc tubulars. I'll see if I can return my White Industries CX disc hub (130mm rear) and buy a standard hub instead for this build.

I'm looking forward to the light weight, easier maintenance, and lower cost of mini-v brakes. I run alloy rims so I don't think I'll have a problem stopping.

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Permalink Reply by Hobbanero on November 5, 2012 at 3:56pm

Geoffrey--

I agree with your comments. I have only been on the BB7s for a few weeks on my new bike. I have a lot of experience with hydraulic discs, including some road riding testing a Volagi. The BB7s are a letdown compared to hydraulics, but I still prefer them in most instances to cantis.

I do some general trail riding on my cx bike. On steep descents, traditional cantis (I have not ridden linear pulls, but hear good things) seem to only retard the rate of acceleration. This can make for exciting moments. While the BB7s don't have the modulation of hydraulic discs, they are a lot better than cantis. I am running 140mm rear rotor, so I don't have the problems you are experiencing with skidding. In fact, I feel like I am short a bit of power back there. I am switching to organic pads, which should give me that little bit extra I would like. It looks like the pros ride 140mm rotors front and rear to give them less power but more modulation, and make the feel more like the cantis they are used to.

I am looking forward to hydraulics. The ride on the Volagi with a TRP Parabox showed that the modulation is amazing and quite useful on a skinny tire.

The setup is fiddly. For the first couple of weeks, every time I removed and reinstalled a wheel, the rotor rubbed. Maddening. I seem to have them dialed now.

I got the screeching noise as well. Should be better with the organic pads. I also eliminated it with the metallic pads by cleaning the rotors with acetone and lightly sanding the brake pads to clean them. I would perform the same maintenance on rim brakes, so not a big deal.

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Permalink Reply by Geoffrey Grosenbach on November 5, 2012 at 9:35pm

@Hobbanero I tried organic pads and still hear screeching. Sanding the rotors and breaking them in properly may help.

I switched to TRP mini-Vs on the front last week and really enjoy them. They were powerful and cleaned quickly even on a sandy, muddy course on Saturday and Sunday.