To handle the demands of an off-road course in winter, we’ve seen a trend towards disc brakes in cyclocross. Most bike manufacturers offer at least one model that comes standard with disc brakes. Yet many of the pros, most notably those in Europe, stick with cantilever brakes.
So, why the trend toward disc brakes? And are they always appropriate?
First, an introduction to disc brakes from Lennard Zinn at VeloNews:
A brief disc-brake primer
Cable-actuated brakes constitute the vast majority of disc brakes used in cyclocross, due primarily to the absence of hydraulic master cylinders built into road dual-control levers until recently.
The models most commonly used in cyclocross are the Avid BB7, followed by the Hayes CX-5.
Disc-brake pads are very thin, on the order of the thickness of a nickel when new, and their spacing from the rotor is very close. And cable-actuated disc brakes generally fade sooner with pad wear than do hydraulic ones.
There are two reasons for this. The most important is that they are not “self-adjusting” like hydraulic brakes. As the pads wear, there is no system to automatically either take up additional cable slack or reposition the pads closer to the rotor.
The other reason is that most cable-actuated disc brakes have only one moving pad.
The brake cable pulls a rotating arm that drives the outboard pad inward by means of ball bearings rolling in curved, tapering tracks. The moving pad pushes the rotor over until it contacts the stationary inboard pad.
When the lever is released, the outboard pad returns by means of a spring, and the rotor springs back to running straight up and down between the pads. This means that the outboard pad hits the rotor sooner and thus wears faster than the inboard one, and it also means that the loss of pad material results in a faster loss of braking than if the cable were pulling both pads equally toward the rotor.
As the pads wear, the user can simply turn the adjustment knobs on each side of the caliper clockwise to move the pads closer to the rotor. This can be done until the pad thickness has reached critical limits, but it can only be done while the bike is stopped; the rider can’t adjust braking on the fly.
A hydraulic disc brake, on the other hand, will continue to offer braking as the pads wear until the pad material is gone.
Hydraulic brakes generally have moving pads on both sides of the rotor and are self-adjusting. The pads wear evenly and have double the movement because the same amount of lever movement results in both pads moving as far as the single outboard pad moves in a cable-actuated setup.
As the pads wear, the brake automatically compensates by taking more fluid from the reservoir at the master cylinder to fill the extra internal volume created by the pistons moving further out in their cylinders to get the rapidly thinning pads to contact the rotor. This continues as the pads wear down, and fade generally does not happen in cold, wet conditions until the pad material is completely worn off of the pad backing plates.
Of course, the pad material is still thin, meaning that riders could still lose their brakes over the course of a race in these conditions. There have been plenty of muddy and slushy mountain-bike downhills in which racers have gone through their pads in the course of a two-minute run, even with top-of-the-line hydraulic brakes with four pistons, huge rotors, and bigger pads with far more surface area than road disc pads.
The three general types of disc-brake pads are:
• Organic (a.k.a., “resin”) pads made of tough, heat-resistant synthetic fibers like Kevlar or Twaron (both para-aramid fibers) bonded together with a petrochemical resin.
• Sintered metal (a.k.a., “sintered,” “metallic,” or “sintered metallic”) pads, which are metallic particles (generally copper alloy) fused together under heat and pressure; they may or may not have some other ingredients as well.
• Semi-metallic pads made of steel fibers mixed with other fibers in a ratio of up to 50-50. These are less common in bicycle applications than in motorcycling.
Disc Brakes at CX Nationals
The ever-changing racing conditions at Cyclocross Nationals this year gave us reason to doubt that disc brakes are always the best choice.
As we reported, the consistency and thickness of the mud varied from day to day, from race to race and sometimes, even, from lap to lap – depending on the temperature and the cloud cover.
The texture of the mud was likened at different times to peanut butter, fudge and thick frosting, always with a hard layer of ice just below.
The varying weather conditions dictated the varied success of braking systems. During the week, the rain and melting snow took a toll on disc brakes. The thin, wet mud on the course meant constant wear on brake pads. Riders with disc brakes frequently lost the ability to brake due to worn pads. Bikes would have to be swapped out each lap so mechanics could adjust the brakes.
David Weber of Team Kappius found he needed to “take a pit bike on every lap, since the pads on his Avid BB7s had worn enough that he could pull his levers all of the way back to the handlebar with no effect. His crew screwed in his adjuster knobs during each bike’s sojourn in the pit, so he had good braking initially on the subsequent lap, but braking effectiveness would be gone again by the end of the lap.”
Snyder Cycling Service mechanic, Chandler Snyder, who worked “on many a distraught rider’s disc-equipped bike on Thursday and Friday,” believed that hydraulic brakes would have been a better choice during the week. However, he added that “the pads are wearing so fast here that they would not last through the race either.”
On the other hand, by Saturday, the mud became so thick, there were many comments that riders were carrying their weight in mud on their bikes. As Lennard Zinn points out, the mud “was mostly thrown away from the center of the wheels. So riders with rim brakes carried a lot more mud dangling from their stoppers, those with mini V-brakes had wheels that barely turned due to the tight mud clearance, and those with disc brakes had mostly clean brakes that worked well.”
On Saturday and early on Sunday, we saw many a rider stop before a remount to try to rid their bike of mud, especially the mud that collected behind their seat posts. The mud would completely surround their cantilever brakes, rendered their wheels almost deadlocked. Not only did they lose their ability to brake, but they were working against greater friction to pedal. For those who raced in these fudge-like muddy conditions, perhaps they would have fared better with disc brakes.
What to Expect at CX Worlds
While we’ve seen an influx of disc brakes here in the U.S., the trend hasn’t caught on in Europe. Yet.
Dan Seaton reported from Belgium last November for VeloNews, “top cyclocross pros still stick-in-the-muds as regards disc brakes.” He found that “an informal survey of the elite men’s and women’s races turned up not a single disc brake. While riders in Europe have embraced new wheel, tire, frame, and drivetrain technologies in recent years, they remain steadfastly faithful to the cantilever brake designs that have hardly changed in decades.”
“If you look at it from a really practical point of view, cyclocross is not a discipline that’s about braking,” said Stefan Wyman, husband and mechanic to British champion Helen Wyman (Kona). “It’s a discipline that’s about not braking… So disc brakes give you a bit of an issue there, because at the moment, with the older technology that is still used in disc brakes —cable technology — they’re very much on or off. And that’s not really what you need in ’cross, you want to be able to feather the brakes.”
Seaton discovered another interesting concern among elite racers Sven Nys (Landbouwkrediet) and Niels Albert (BKCP-Powerplus). “They found the noise that muddy discs sometimes make as they rotate to be highly distracting, an unacceptable tradeoff in a discipline that requires complete concentration.”
One pro who told Seaton he would be excited to try racing on discs was American Jonathan Page. Page went on to reclaim the throne of Cyclocross National Champion in Madison earlier this month. And Helen Wyman has been asked by her sponsors to test a disc brake version of her bike.
Both Nys and Page prefer disc brakes on their mountain bikes. Nys told Seaton, “There are some dangerous downhills…where disc brakes give you a little more control over your bike.” Page said, “I love [disc brake technology] on a mountain bike, it makes a big difference when you’re just braking with one finger, so I can see how it would be an advantage.” We just might be waiting for the technology to be adapted to better suit cyclocross.
Nys told Seaton, “In the future… when the bikes are ready and when Shimano and SRAM are ready, I think we’re all going to race with disc brakes.”
Despite his reluctance, Niels Albert conceded, “I think in two or three years everybody will be riding discs.”
While we probably won’t see many disc brakes among the pros this year in Louisville, we’ll see a few. And, like Nys and Albert, we suspect we’ll see even more disc brakes in the years to come.