While mountain bike brakes are designed to withstand intense riding conditions, they generate significant heat during braking. If you've ever bumped your leg onto your rotor after a long descent and ended up with a painful new tattoo, or even splashed some water onto your rotors to hear the sizzle after a long downhill, you'll understand just how hot they can get.
If your brakes get too hot, you can get glazed pads or burnt rotors. In ther short term, you caould heat up the fluid and lose pressure, or lose braking altogetehr. And some brake "pump up" or feel more solid as they get too hot.
But what makes MTB brakes get hot? Is there anything you can do to reduce brake fade or lever pump? Well, as it turns out we can change some components or even alter our riding style to make sure out brakes don't overheat all the time.
Here are 5 reasons your MTB brakes get hot, and some quick pro tips to get more out of your brakes:
When you squeeze your brake levers, you convert the kinetic energy of your moving bike and your body into thermal energy. The higher the speed at which you are traveling and the more energy you need to dissipate and the more heat will be generated. All this heat needs to go somewhere, and in the case on MTB brakes it's the rotors, pads and calipers that take the brunt of it. Big hills generally mean more speed and more braking, so if you ride big mountains regularly or travel to them for riding holidays, you'll want to make sure your brakes are up to the job.
PRO TIP: Some have said that bigger riders are more prone to excessive heat build up in their brakes, but the physics of braking highlights that faster riders can still get excessive heat build up, regardless of how big they are or how much their bike weighs.
After any braking, the heat generated needs time to dissipate. Continuous braking without allowing sufficient intervals for cooling can lead to excessive heat buildup and potential brake fade. Skilled riders generally separate short, hard braking with longer periods of time off the brakes compared to beginners. When you ride while the brakes are off, air travels past the rotors and caliper, taking heat away along with it. In that case, speed can help your brakes cool faster, so long as you're not constantly using them.
PRO TIP: We've found that riders can begin to separate braking events in their Key Opportunities by practcing to concentrate their braking or taking smoother lines, rather than riding their brakes through the entire section.
The size and mass of the rotor play a crucial role in heat management. Larger rotors provide increased surface area for heat dissipation, allowing the heat to spread out and dissipate more efficiently. Additionally, larger rotors tend to have more mass, which can act as a heat sink, absorbing and storing more heat. While being able to store more heat might not necessarily sound good, it's better to direct heat to the large rotor area than haing it build up in the pads, braking surface or caliper.
PRO TIP: You have to check out this video on rotor size!
The choice of pad material significantly influences heat generation and dissipation. MTB brake pads are commonly made of either organic (resin) or metallic compounds. Organic pads generally have better initial bite and modulation but tend not to be able to store too much heat themselves. This means that the heat must be passed on to the rotors (a good thing!). Metallic pads on the other hand, handle heat better but may lack initial bite and modulation. Metallic pads can absorb a lot of heat, but that means the braking surfaces may operate hotter and therefore risk overheating.
PRO TIP: While MTB brake pad material is generally a personal choice, many pros opt for resin/organic pads. They do this because of the high speeds they ride at and extreme braking they do - and they say resin pads help to save their rotors.
Mass of the Caliper
The mass of the caliper itself affects how your brakes can tolerate heat. Heavier calipers tend to absorb and retain more heat, reducing the overall heat transferred to other brake system components. If you're riding big hills or riding very fast, a heavier caliper can store heat for longer so that your brake fluid or braking surfaces don't exceed operating temperatures. However, excessively heavy calipers can negatively impact the bike's weight distribution and handling characteristics, though MTB brake calipers are generally light in the grand scheme of things.
PRO TIP: While the 4 piston trend doesn't lend to better or more powerful brakes in and of themselves (more on this another time...), they do force manufacturers to develop larger calipers. These larger 4-piston calipers have more mass and therefore greater capacity to store heat.
Brakes can't be stopped from generating heat, so we need to figure out good combinations of components and techniques to deal with high speeds of modern MTBs. By considering the speed and energy involved, allowing time for cooling, choosing an appropriate rotor size and pad material, and optimizing caliper mass, riders can ensure their brakes operate within safe temperature limits and maintain optimal performance.