There’s nothing quite like biking through the mountains on your trusty MTB. Sure, it’s hot out, but cycling at such great speeds lets the wind run through your hair and cool you down.
All seems well until you brake and take your foot off the pedal and rest your leg against the rotor, only to find it’s hotter than it’s ever been before!
How hot can MTB brakes get? Why are your MTB disc brakes overheating, and what happens when they do?
Most importantly, what can you do to stop them from overheating?
Keep reading to find out!
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How Hot Can MTB Brakes Get?
Mountain bike disc brakes can become 800 degrees Celsius.
Believe it or not, your mountain bike’s disc brake’s temperature can reach up to an incredible 800 degrees Celsius (or 1472 degrees Fahrenheit).
That is more than hot enough to severely burn you if you accidentally touch the brakes with your calf or hands.
What Happens When MTB Brakes Overheat?
Three things could happen to your MTB when its brakes overheat.
Luckily, none of these scenarios pose an immediate danger if quickly noticed and fixed by the cycler.
However, since MTB riders are often preoccupied with more imminent threats, like trying to avoid falling off a mountain, these issues tend to go unnoticed.
Let’s look at how overheating affects your mountain bike’s brake fluid, disc brakes, and general riding experience and safety.
Your Brake Fluid Could Boil
One of the risks of your disc brakes overheating is that your brake fluid could boil.
Brake fluid, like mineral oil, doesn’t boil like water on the stove. Instead, brake fluid drastically heats up and expands inside its rubber tubing. This causes the fluid to become less dense.
This, in turn, prevents your disc brakes from compressing the disc and stopping your bike, causing your brakes to completely give out.
Given that disc brakes can heat to 800 degrees Celsius and mineral oil’s boiling point is a mere 310 degrees Celsius (or 590 degrees Fahrenheit), the probability of this occurring is more likely than you may think.
Not only is this dangerous, especially for mountain biking, but it often happens too quickly for riders to notice until it’s too late.
Your Brake Pads Could Melt
Another thing that could happen when your disc brakes overheat is that your brake pads could melt.
This phenomenon is also known as glazing since the pad melts and liquefies, often coating or glazing the rotor.
Disc brakes need friction in order to function properly. However, the pad’s oily material will decrease the friction between the disc brake and rotor, allowing the rotor to continue turning despite the brake’s compression.
You risk being unable to slow down or stop your mountain bike, which could be catastrophic.
Your Disc Brakes Could Wear Down
Disc brakes must remain in good condition, so you must replace them when you notice they’re beginning to wear down and lose their effectiveness.
Overheating can quicken this process, costing you more money in frequent replacements.
If left unattended, you could suddenly realize your brakes aren’t working at the worst moment possible, like when riding down a steep hill.
Luckily, disc brakes are relatively inexpensive and easy to replace. So, regularly check your brake’s condition, especially before going on long, treacherous rides in nature.
Why Are My MTB Disc Brakes Overheating?
Your disc brakes could be overheating for a few different reasons.
So, we know what happens when your disc brakes overheat, but why are they getting so hot in the first place?
Disc brakes overheating is very common and there’s usually a simple explanation behind it.
Worn or Melted Brake Pads
Your brake pads are meant to soften the collision between your brakes and rotor. However, when they’re worn, the brake’s metal could be scraping against your rotor, creating friction.
Hearing a scratching sound every time you brake is a pretty good indication that this has happened.
This friction creates heat, causing both your disc brakes and rotor to rapidly overheat.
This can also happen if your brake pads have melted, perhaps from previous overheating. As discussed, not only does this decrease your brake’s efficacy, but it also causes more overheating.
Dragging Down Hills
One of the best things about mountain biking is feeling the thrill of riding down hills after an exhausting ride to the top.
As any seasoned biker knows, you must use your brakes to control your descent and avoid losing control of your bike’s speed. A popular way of doing this is by dragging your bike’s brakes by continuously pressing them during your descent.
However, this can create a lot of friction since your bike’s rotor continues to spin while being compressed by the disc brakes.
This continuous and prolonged friction can cause overheating, leading to your brake pads wearing down and possibly melting.
Excess Weight
Excess weight on your bike could be a contributing factor to the disc brakes overheating. This could be a result of whatever heavy gear you’re carrying or your own body weight.
To understand why this happens, we can look at this equation Mass x Velocity = Momentum.
The higher an object’s momentum, the more difficult it will have to stop completely.
So, if you’re putting a lot of weight on your bike and going very fast, it’s going to be harder for you to stop than for someone of a lighter weight going slower.
This momentum makes it more difficult for the brake pads to completely stop the rotor’s movement, creating friction.
How Do I Stop My MTB Brakes From Overheating?
Let’s go over a few things you can do to prevent your MTB brakes from overheating.
All of these suggestions can be done individually or together, depending on how hot and frequently your brakes overheat.
Frequently Replace Your Brake Pads
The first, and easiest way to decrease overheating is by frequently replacing your brake pads.
No matter what kind of brake pads your bike has, it’s important to regularly check how worn they are and replace them when needed.
If you go on long rides through hilly mountains, you may need to replace your brake pads more frequently, or even bring some replacements along with you.
Control Your Brake Usage
Dragging your brakes while riding downhill is a huge contributing factor to overheating.
However, you can lower the brake’s heat by using proper braking techniques.
Instead of holding down your brake the entire time you descend, try lightly pressing and then releasing the brake levers. This will slow your bike without the brake pads continuously clasping the rotor.
Just ensure you do not grasp the brake levers too tightly, or you could fly off your bike and injure yourself. This method takes some practice, so try it on a smaller hill before using it on steep slopes.
Decrease Your Bike’s Weight
Decreasing your bike’s weight, which includes your bike’s frame, you, and any gear you’re carrying, is essential if you want to prevent overheating and have a smooth riding experience.
For instance, If you’re a heavy-set individual, your body weight could be contributing to your brake’s overheating.
To decrease your bike’s weight, consider replacing certain bike parts with lighter versions, like its rotor, wheels, handlebars, etc.
You should also be mindful of what you’re carrying with you and try to lighten your load as much as possible.
Invest in Finned Brake Pads
If you’re in the market for new brake pads and want to further prevent overheating, consider investing in finned brake pads, like the SHIMANO J03A Resin Disc Brake Pads .
These aerodynamic brake pads have a finned, aluminum surface, which allows for the heat to flow through the pad’s gaps. This ventilates your pads and rotors, decreasing the risk of overheating.
Also, since the brake pad is made of aluminum, which can dissipate heat at a much faster rate than other metals, it drastically decreases the likelihood of your brakes and rotor overheating.
Invest in an Aluminum Spider Rotor
The type of rotor your bike has greatly impacts whether it will overheat or not.
There are many rotors on the market, from hefty, thick stainless steel ones to lighter and thinner models.
Each one of these models serves its own purpose, and aluminum spider rotors are specifically designed to combat overheating.
They also have a stronger braking power, reducing the friction that occurs when the brake pad compresses the moving rotor.
Since the outer disc is made of a sheet of aluminum between two layers of stainless steel, it’s durable enough to not bend or snap if you excessively brake.
If you’re interested in buying an aluminum spider rotor, check out the SHIMANO XT SM-RT86 Rotor - 6-Bolt for a high-quality, durable rotor proven to dissipate heat.
To learn more about the benefits of aluminum brake pads and rotors, watch the video below.
Wrapping Things Up
Your bike’s disc brakes overheating can be alarming, but there are ways to prevent it.
They’re usually overheating due to the friction between the brake pad and rotor, so decreasing this friction by regularly changing your brake pads, controlling your brake usage, and decreasing your bike’s weight is a good place to start.
You can also invest in aluminum finned brake pads and a spider rotor to further mitigate the heat.
What’s your experience with disc brakes overheating? Let us know in the comments below!