Brakes tend to be a polarizing component–everyone has their brake brand of choice for various reasons, be it ease of service, fluid type, modulation or lack thereof, tune-ability, bite point etc. But they all have one thing in common–they have to slow us down, and they have to do so safely and reliably.
Brakes have a damn hard job when you think about it. Slowing down a rider at speeds up to and in excess of 40MPH, with a combined weight of around 180lbs on average, on dirt, at all times of year and in all conditions. It’s a tough job, and modern bikes have us riding harder and faster than ever, pushing our brakes to the limit, mostly with very little in the way of maintenance. Mountain bike brakes take an absolute beating like few other components.
Here in B.C., brakes have a particularly tough time. Descents often have more than a thousand meters of steep, rowdy, vert in one go, and days in the bike park multiply that. It’s no surprise then that as a frequent rider and a bike mechanic in a North Vancouver shop, I’ve seen my share of funky brake problems. Getting to the bottom of the reason why and what we can do about it isn’t quite rocket science, but there is certainly a good deal of science involved.
Mountain bike brakes versus auto brakes
Jude Monica, Tech Rep at Magura USA tells me that high end cycling brake systems can be considered “race level.” Riders typically outweigh their vehicle by four or five times, compared to automotive or motorcycle brakes and don’t have a comparable transmission to allow engine braking. He raises a fair point that the operator to machine weight ratio is pretty damn high, with mountain bikes having to put up with a lot while weighing comparatively little.
Also while we’re comparing mountain bike brakes to motor vehicle brakes, which tend to require less maintenance while seeing much higher speeds, weights and mileage, we need to consider the fact that they’re designed for a much different application, and that size and weight are much less of a constraint.
Monica also said “automotive systems are overbuilt in every comparable piece of the systems including fluid volume, rotor thickness, caliper size, etc and they are much less stressed on a daily/hourly basis” adding that automotive hydraulics operate with much larger inside diameters of the lines.” With diameters half the size as auto brake lines, mountain bike brakes have “higher pressures internally due to this and therefore can encounter more potential complications.”
Mounting brakes on mountain bikes
Sam Gibbs, Design Engineer at Hope Tech agreed, but added that cycling brake systems are limited not only by weight, but the packaging within the post-mount standard,
In the automotive world, “they have a lot more space and aren’t so concerned about weight so seals can be larger and more robust, pads can be larger with more surface contact, discs and calipers can have more mass all helping consistency and reliability,” said Gibbs.
Automakers also have the advantage of scale and don’t need to stick to certain standards for things like brake mounts, instead producing their own for hundreds of thousands or even millions of vehicles and thus they can produce them exactly the way they want without the constraint of industry standards that face mountain bikes.
Gibbs also notes that the leverage ratios are much different. To slow down a bicycle, riders use their hands which have a relatively low face which requires multiplication to produce the proper force.
This means that the entire system has to be set up incredibly precisely to perform well. Compare this to a motor vehicle where “in a car the input is by foot so there is a higher force activating the system, then they are vacuum or electrically boosted which helps to keep the multiplying ratios down along with a large disc diameter compared to the wheel diameter.”
Considering the above factors, we can say that high end mountain bike brakes are some of the highest performance components of almost any industry, despite seeming relatively simple on the surface.
Favored fluids and performance vs. reliability
The nature of high-tech, high-performance parts of course comes at the cost of higher maintenance which should not be surprising. While we are right to expect that for a given performance level, contemporary components should require less maintenance than previous generations, we now have higher performance too, necessitating more maintenance. We are, however, starting to see trends toward lower maintenance though.
Component giant SRAM for example who have long been a stalwart of the use of DOT fluid in brakes for its performance benefits recently released the DB8 brakes, that use mineral oil for its lower maintenance requirements, despite inferior heat management properties. SRAM states that is the biggest difference in the two fluids: DOT fluid has higher performance and mineral oil is more reliable.
Without getting into the debate of mineral oil vs DOT fluid, we can safely say this is a step forward in terms of consideration for the end user. Chris Mandell, public relations manager at SRAM, says that they also use DOT 4 for the factory bleed in their lower end brakes and DOT 5 in their RSC and Ultimate level brakes for the same performance/reliability trade-off for the end user.
Brakes are of course constantly improving, and engineers are always trying to solve problems. Nathan Silberman, marketing coordinator at Tektro USA says designing a brake that is “both robust and lightweight without compromising on affordability” is a challenge, and that size, weight and form factor are the main problems.
Gibbs says Hope have found similar limitations in that they are limited mostly by packaging post mount and hub offset standards, and as a result of this most brake designs tend to lead down a similar path.
“Performance vs. reliability is probably the hardest to solve as they tend to be the inverse of each other.” Innovation leads to improvements that do make a difference, but the design of a new brake tends to be “evolutionary rather than revolutionary. When it comes to brakes it’s the small details that really matter,” said Gibbs.
Making good brakes better
TRP’s hydraulic mountain bike brakes have capitalized on 2.3mm thick rotors instead of the typical 1.8mm for more power and better heat dissipation, which SRAM followed with their latest HS2 rotors, a great example of a small evolution in brake technology leading to a vastly improved product over time.
Mandell also mentioned that SRAM engineers are always testing their products to the limit, using test equipment that’s been specifically designed to recreate some of the worst cycling conditions known to man. They even go as far as sampling dirt from the Cape Epic race and having an industrial partner recreate it specifically to cover brakes and other components during testing. There’s a lot that goes into a modern brake behind the scenes such as improved sealing and specially developed rubber seal compounds that aren’t particularly inspiring from a marketing perspective but are instrumental in the improved reliability of our brakes.
For the most part, funky manufacturing issues aside, and as a seasoned bike mechanic I can confidently say that serious issues are few and far between. Most problems with modern mountain bike brakes tend to be either setup or maintenance related. As Monica says, high end brakes are F1-level systems, and setup is an important part of this.
Gibbs stressed the importance of setup and that if a brake has a good initial bleed, problems down the line that are often attributed to air in the system are usually not related, and could in fact be symptomatic of one of many other problems, such as uneven pad or rotor wear as a result of uneven piston movement/spacing, or even a warped rotor. Any of these seemingly minor things can have a significant impact on lever feel and power.
Mandell echoed this, saying that piston rollback, or how far the piston retracts when the lever is released is an important factor in the feel of the brake, and that SRAM is always trying to improve this. He also says that a proper bed-in procedure is incredibly important to achieving optimal brake performance.
Despite SRAM and Hope disagreeing on whether or not to lube pistons–SRAM says don’t, Hope say do, everyone agrees that one of the most significant factors in brake performance is keeping the brake clean. (Check your brake manufacturer for their recommendations.)
Regularly cleaning the caliper involves removing the pads and cleaning the inside using brake cleaner or alcohol, and will keep the brake operating smoothly for much longer. A dirty brake caliper and therefore dirty pistons and seals can result in pistons that are reluctant to move, improper pad/rotor spacing, sticky pistons, uneven pad wear, leaky pistons and more.
Outside of this, some basic maintenance is really all that’s needed to keep your brakes operating smoothly. These include:
– Bleed once a year if DOT, every two years if mineral oil
– Check pad wear and replace pads when they’re worn
– Check rotor thickness and replace when worn
– Check for uneven pad/rotor wear and replace accordingly
– Clean caliper/rotor and ensure proper piston movement
– Properly space pads/rotor when installing
– Properly bed them
– Use OEM fluids/pads/rotors
– Do not overspray chemicals/lubricants near brakes
– Ensure rotors are straight
Of course how much you spend on a brake system will have an influence on brake performance. It can’t reasonably be expected that a brake costing half as much performs as well as a top level brake. However even entry level 4-piston offerings can be pretty damn powerful, but you might find they require a little more maintenance to keep them performing like they did when new. Following the above pointers however will go a long way to keeping your stoppers in tip-top shape.
But, we’re pretty damn lucky with where modern bike performance is at. Brakes are certainly much better than they used to be, and while there are always going to be certain areas and people that are harder on components we’re in a much better place overall.
It may be worth reminding ourselves of times gone by when the best we had were Avid Juicys or Hayes Nines on our trail bikes and how far we’ve come since then. For those of you that haven’t been in the sport that long, just trust us.
One of the biggest things that folks should take away from this is to maybe pay more attention to their brakes. Take the extra time to clean your caliper every now and then, particularly when replacing pads. Check your rotor is straight and check your pistons for good movement and take the time to set your pad spacing properly. Take a look at our brake setup guide here or our caliper service guide here and give your brakes the love they deserve.
Good read, Sam.
Add to the list…
Always degas DOT fluid! Never omit this step if you want a long term bleed without drama!
Always use fresh fluid from a well sealed container.
That takes a minute or two but eliminates the “Be back”, a custy returning since air is still in the system because it is absorbed by the fluid. Even a freshly opened container will have some air in the fluid. Water is another issue with DOT since it is absorbed by the fluid.
The convenience of DOT is that it cleans up with something really cheap and readily available, water!!
DOT 5 vs. 5.1…
DOT 5 is silicone based and can cause trouble with seals. Not recommended for bicycle use!!
5.1. Very similar to DOT 3 or DOT 4 and is recommended for bicycle brakes.
The largest improvement to bicycle hydraulics is heat control and dissipation! By changing a few things, this has been brought to be more reliable and brake fade and failure caused by excessive heat is a thing of the past. For the most part…