Technical FAQ: Ideas for disc brakes in wet conditions

Lennard Zinn fields questions and recommendations for improving mechanical disc brake performance in conditions like those at ’cross nationals

Editor’s Note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

Lessons from motocross

Dear Lennard,
I just read your article on the failures of disc brake systems in the abrasive mud in Wisconsin. Even with hydraulic brakes I am sure they wouldn’t last a complete race with the terribly thin layer of material on the pads. The only way we make them last the whole race (in motocross and off-road) is by using a solid rotor. The groves or holes in vented rotors allow the abrasive mix to fill in these voids, and every time the brake is applied it is like coarse sandpaper on the pads. With solid rotors, each time the brake is applied the mud is pushed completely off of the rotor surface. While brake performance is reduced with solid rotors, you at least have brakes for the entire race, and I don’t think they would require adjustment each lap.

Nothing against the wavy rotors although I personally think it’s nothing but aftermarket companies that created a desire for them. A complete round rotor is stronger (in my opinion).

The holes or slots in a rotor give the mud a place to be pushed into, the heat from braking cooks the moisture out of the mud, and it becomes baked into the holes or slots and the rotor is now an abrasive disc. I’m not guaranteeing a solid disc would be the cure all for a complete race, but I think it’s possible. I also would try slotting each pad in an X pattern just to give the mud from the first few applications of the brake a place to reside. With a solid rotor, once the slots in the pads are full it’s not hurting anything. If those slots in the pad give you any added pad life in a race then it’s a benefit. Cut wide slots in the pad too. Yes, some will say you will lose braking power but how much brake do you need in the mud?

I have been a mechanic for many years in pro motocross and GNCC off-road racing. When we encounter a race where the conditions are soupy mud we have to use solid rotors. Even in the shorter races of MX, the brake pads wear so fast with vented rotors that you are running a risk of losing all the pad material. When using solid rotors, I have had plenty of material left on the pads even after a three-hour off-road race in abrasive mud.
—Wyatt Seals, Husqvarna Motorcycles North America

Dear Wyatt,
That’s great information! I just don’t know if solid rotors exist in the bike industry. I perused the photos of all 80 rotor types for sale in the Quality Bicycle Parts catalog, and every one of them had holes in it.

Your experience with a dramatic increase in pad life in those conditions by using solid rotors would explain why the wear rate on cantilever pads was not extreme during the same races Wednesday through Friday at cyclocross nationals. Once the pads hit the rim, they squeegee mud ahead of them rather than letting additional mud underneath. But if the rim were peppered with holes like a disc rotor, I’m sure it would fill with grit and grind the pads down in no time.

Pad choice in Belgium

Dear Lennard,
I read that article about the disc brakes! A big change to the “all is so amazing” stories that we have been hearing about them so far in cyclocross. I remember a few of my own mountain bike races in Belgium where my pads were gone in no time and I ended up running downhill because my bike would not stop anymore.

If you are looking for some pads that last: I have been very lucky with EBC gold. They are a U.K.-based company. I could normally last with two sets per winter after making sure to break them in carefully by riding a mile or so with dragging brakes under dry conditions.
—Ard Kessels, C-Bear Ceramic Bearing Solutions for Bicycles

Dear Ard,
I just ordered a couple of pairs of those EBC Gold pads from QBP for myself!

Rotor testing with Ryan Trebon

Dear Lennard,
Not all sintered pads are the same. Different manufacturers use different materials and blends for their pads, even though they all say “sintered” or “metallic.” We found a huge difference in both ultimate wear and also wear patterns between SwissStop and SRAM pads.

We have also found that the rotors make a huge difference in pad life and wear patterns. Some of the rotors that have smaller holes don’t clean out as well and wear the pads faster. Ryan and I went through four different rotor styles before finding one that worked well in the mud. We have the SRAM G2 rotors on all of the bikes. Better wear and the riders say they feel more positive.

Also, it was pretty dry this season. It’s hard to figure out a good setup for mud when you don’t race in it that often.
—Dusty Labarr, mechanic

Clearly, experimentation with pads and rotors is critical. If solid rotors are not available, perhaps the next best thing for those conditions is a rotor with large holes…

Pad choice and heat sensitivity

Dear Lennard,
I think this is a problem with pad material; pad materials are heat sensitive. There can be as many as 60 different components that make up a brake pad compound. Many of these ingredients are activated when heated. The blends of these ingredients make up each compound’s characteristics. Initial bite or torque, and temperature range are some of the more common characteristics that drivers consider when picking a pad compound. Companies like Hawk Performance and Wilwood Engineering make a wide array of pads with different compounds for different racing situations.

We really need someone like Hawk Performance to look into this; they are experts on pad materials and probably can make some suggestions as to a compound to get results. This is something that bike engineers have little experience with, in comparison to racecars.

It’s not a brand-related problem

Dear Lennard,
Cool stuff on the disc brakes. Keep that tech stuff on what the pros ride coming!

Dear Garrett,
Disc brakes are certainly here to stay in cyclocross, but there are still some bugs to be worked out. Unlike their first “sweep” in which one of the podium finishers rode 80 percent of the race on cantilevers, the first complete, race-long, elite-level disc-brake sweep of the men’s podium in cyclocross that I know of happened on the following day, day 2 of the Derby City USGP. The top four were all on disc brakes, in fact, on a second straight dry day of racing.

I am confident that disc brakes will continue to gain ground in cyclocross and perhaps completely replace cantilevers, but not with the kind of wear rate that happened during the weekday races in Madison before the mud thickened up for the weekend. I remember watching the Big Bear downhill on a rainy day with lots of snow still on the mountain – thin, soupy mud conditions similar to Wednesday through Friday’s races in Madison. Many riders that day at Big Bear were getting to the bottom of the hill dragging their feet because their pads were gone after a two-minute run, despite having hydraulic self-adjusting brakes. The friction material was ground completely off of the metal backing plates. I didn’t notice what sort of hole patterns their rotors had.

I also want to make sure that anyone reading this is clear that I in no way think that the problems encountered in Madison prior to the weekend races were brand-specific. Since the vast majority of disc brakes used in ‘cross are Avid, followed by Hayes, it is natural that the feedback from riders will be on those, but I’m certain that the Shimano or any other brand of mechanical disc brake would have had similar issues in those conditions.
― Lennard