Technical FAQ: More on disc brakes in cold weather

There’s plenty more cold-weather riding to be done this winter. Even though 2014 was somewhere between the first and sixth warmest year on record in terms of global average, the Midwest and eastern U.S. had a colder than average winter, and 2015 started out cold there, too. We here in Colorado have traditionally been spared the freezing rain those areas get, but not this winter! Geez. I have a lot of empathy now for those farther north and east of us who have, for their entire lives, put up with this stuff freezing all over everything.

I already posted some answers to the question of what kind of disc brakes to choose for extreme cold, but there is a lot more to be said about it. Don’t be surprised if I find more to add to this in coming weeks, too!

When making purchases for this purpose, I also recommend seeking out bike shops that have employees who ride year-round in your area.

— Lennard

From Avid/SRAM:
In our testing, mineral-oil brakes are more challenged in cold (-15F and below) because of the constraints of the seal material, rather than the fluid itself. As you know, DOT brakes and mineral-oil brakes require different seal materials. We find that the brakes lose rollback at the caliper as the seals get cold, and this is what primarily tips things in favor of DOT brakes.

I would basically rank things as such: Down to around -15F, hydraulic brakes will work the best; some may develop a sluggish feel based on the quality of the product. Below that, DOT brakes will hold up better, but below -30F, if you really need to ride your bike, mechanicals [cable-actuated disc brakes] will be the most reliable — if you can move your fingers enough to pull the lever.

DOT absorbs water; this is true. The fluid is designed to do that as a way of managing air and moisture that enters any system over time.

Mineral-oil brakes still ingest water over time; however, the fluid repels this water, and it collects at low points in the system, i.e., the caliper. The caliper obviously sees higher temperatures, and since water’s boiling temp is basically 100C, this phenomenon handicaps the heat management of mineral-oil brakes.

— Paul Kantor
Avid/SRAM brake product manager

From Borealis (fat bikes):
We have had a ton of experience on a ton of different brakes, and for wet/cold areas we would recommend a DOT fluid brake, as opposed to a mineral-oil brake, like a Shimano. I love Shimano brakes, but when I rode the 988 trail brakes in the cold last year, the performance was very poor and lever feel was slow and unresponsive. I actually thought the crappy SRAM X0 brake system had better performance in cold, snowy conditions despite the loud, strange noises they make. The new SRAM guide brakes are the best multi-use brake on the market currently, in our opinion. The lever action in the cold a couple weeks ago, when it reached about 10-14 degrees F, was actually pretty good, and the braking performance of that four-piston brake is amazing with a sintered, metallic pad. Many of our Canadian and Alaskan dealers use mechanical brakes because of extreme temperatures, so it really depends on what the customer is looking for. So for cold weather, use a SRAM Guide brake, and for extreme cold we would recommend going with a cable-actuated brake like Avid’s.

— Greg Herrman
Founder, Borealis Bikes, Fatbike.com

From Hayes Disc Brakes:
– Any of the mentioned systems can be made to operate at low temps. The most important thing is that the manufacturer performs low-temperature testing and makes any necessary adjustments, which we have done for our mineral-oil brake, glycol (“DOT”) brake fluid systems, and mechanical systems.
– The biggest difference we have observed is that mineral oil has less viscosity stability in cold temperature than brake fluid. It becomes thicker, and it can exhibit a noticeably slower lever feel. Glycol fluids do this too, but to a much lesser extent, in our experience.
– Our benchmark testing has shown many manufacturers’ mineral-oil products do not seal as well as glycol fluid systems at cold temperatures. Mineral oil requires the use of a different seal material, which changes elasticity (or “durometer”) with temperature. Special design considerations must be taken to ensure proper sealing.
– All hydraulic systems will have a different feel in cold temperatures. Mostly due to the fluid viscosity and seal durometer changes, the lever will feel heavier, and the caliper piston retraction (and hence pad clearance and lever dead stroke) can change. In our testing, the glycol systems were generally more robust to temperature.
– Cable systems are generally less sensitive to temperature, but they also will have a heavier lever feel as assembly grease and any cable lubrication thickens with temperature. They also do require some exposed cable that can ice up in rare conditions, so they’re not totally impervious to weather. And even at their best, cable systems do not match the smooth, linear, and low-effort feel of a hydraulic brake system
– Cable/hydraulic systems are a way to bring a mostly hydraulic system to a drop-bar bike at a reasonable price point. But they have all the drawbacks of both hydraulic and mechanical systems and due to their complexity, I would opt for either a mechanical or hydraulic system for use in adverse weather.
– Using brakes in snow is very similar to using them in rain. The snow melts to water when in contact with the rotor, so I would recommend wet-weather pads. Most of the time, fully sintered metallic pads offer the best wet-weather performance and also perform well in snow.
– Our fleet of test riders consistently prefer carbon-fiber lever blades in cold temperature. It doesn’t conduct heat away from your fingers nearly as quickly as aluminum. It seems unlikely, but it makes a noticeable difference.

— Tim Abhold
Director of Engineering and R&D
Hayes Components

From a guru of Alaska winter endurance riding:
The first hydraulic brakes I ever saw were in the early days of the Iditabike. Those Maguras were working happily at -30F.
The hydraulics-in-the-cold story is pretty straightforward. The DOT systems behave well down to at least -50F. Mineral-oil systems show slower retraction starting in the -20s or so but still perform well as far as braking.

Riders have a variety of problems with their bikes in winter; some problems get misdiagnosed, and hydraulics are an easy target. Many dedicated winter bikes here get set up with [Avid] BB-7s [cable-actuated disc brakes] as a sort of insurance. I don’t discourage this practice.

Brakes themselves are rarely a problem in our winter conditions. The available traction on snow or ice limits braking more than the rest of the system does.

Freeze/thaw conditions, whether from the weather or from bikes going in and out of warm spaces, cause a lot of mechanical problems. Bike leaves house warm, snow thrown up by tires melts on brakes or derailleurs, then freezes as bike cools. Hydraulics are less subject to this.

Lubriplate and Castrol offer low-temperature hydraulic fluids. I’ve never explored these options, because we haven’t needed to. Looking for some quantitative information for you, I learned that Citroen and Rolls Royce use(d) mineral oil, and that Castrol makes low-temperature fluids for those systems too.

I also learned that smart brake and suspension automotive systems need fluids whose viscosities remain in a narrower range than is needed for older systems. The antilock on my cars hasn’t acted differently at -50F, underlining the fact that even basic DOT fluid is pretty temperature-invariant.

Rereading the question:
Cables will act like cables at all temps
DOT systems will be a bit less trouble-prone than mineral oil at very cold temps.

— Simon
All Weather Sports
Fairbanks, AK

From Surly:
DOT fluid is the way to go if you must use hydraulic brakes in cold temps. Mechanical brakes also work well. We spec Avid hydraulic brakes on our Ice Cream Truck specifically because they use DOT fluid. I personally prefer Shimano disc brakes for their performance attributes but I would never use them in the cold, because they have mineral oil in them.

— Peter Redin
Brand Manager – Surly Bikes

From Larry Kaatz of QBP (Minneapolis):
Even stainless steel rotors can get a little messed up with road salt (used liberally around here), and if you don’t wipe them down well after rides on roads with salty slush and/or puddle they’ll be noisy and rough at the start of your next ride. Using the brakes will clean off the rotors so that they’re quiet again, but I’m not sure what that means for the lifespan of the brake pads.

— Larry

From Lance Larrabee of TRP brakes:
With the cold spell here in Utah and most of the U.S. coinciding with our need to prove some of our new designs, TRP has recently been conducting cold weather testing on our own hydraulic disc brakes brakes as well as those of our competitors. We found at temperatures below 20F degrees, all hydraulic disc brakes in our test, both mineral-oil and DOT fluid, showed some degree of sluggish performance. We didn’t experience any catastrophic failures and all the brakes returned to normal function either as the brake heated up from friction or when the weather got above freezing.

Many fat bike riders, especially those from cold-weather states like Alaska and Minnesota, who often ride in extreme cold weather, have experienced the same symptoms and from our perspective at least, seem to have come to the consensus that mechanical disc brakes (cable) are the best option in the cold.

Following the introduction of our two-piston mechanical road/cross brake, the Spyre, we had many request to create a mountain version of Spyre specifically for fat bikes. As a result, we created a second two-piston brake to work with flat bar linear pull-type brake levers and to cope with the addition rotating mass of fat bike wheels. We named this new brake Spyke and introduced it in early 2014. In addition to the change in lever pull and strength, the Spyke has a snow/mud cover over the pads and an accordion boot to help seal the cable at the actuation arm.

If you’re creating a drop-bar winter training/commuter bike, the snow/mud cover and accordion boot can easily and inexpensively be added to our Spyre mechanical disc.

— Lance