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  1. #1
    Trail Cubist
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    How much heat can disc brakes take?

    So last night, while riding down a VERY long, steep and technical (really rocky) stretch of singletrack, I reached a milestone in my short MTB career: I smoked my brakes! (As in, they literally started smoking!)

    I weigh about 220lbs, and the descent was so rocky and steep that I had no choice but ride both brakes pretty hard continuously. Alternating between front/rear just didn't cut it because I'd start picking up speed using only one brake (and I was worried I'd fry a single brake even more quickly).

    I got concerned and stopped. I touched the caliper housing and almost burned my fingers. Then I squirted some water from my Camelbak onto the pads, and it literally sizzled and evaporated (like a hot skillet). I was kinda blown away.

    So my noob questions are...

    How much heat can disc brakes take? (e.g. how often should you stop to let 'em cool down on brutal descents?)

    And once you've heated up the brakes that much, should you replace the pads?

    Thanks,
    Scott
    29er wheels are dangerous. They may cause you to go faster which can result in serious bodily injury. óJim311

  2. #2
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    Cooking your brakes happens....

    Beginners tend to cook them alot more than people with more experience...

    Try to brake with short stabs rather than feathering the brake all the way down the hill.

    The first symptom will be brake fade, and sometimes squealling.

    That is the time to stop and let them cool off a little bit.

    Once cool everything should work as it did before if not you have:

    a) glazed the rotor.

    b) worn out the pad.

    c) badly cooked the fluid.

    First fix, lightly sand the rotor and the pad.

    if the brakes are "soft" bleed them.

    Worst for me was going down Mauna Kea, cooked them at 75 kph on a 17% grade, took about 2 km to finally get stopped. Brakes were fine and I continued on down the mountain to the ocean.

    Now I have a 203 rotor on the front.

  3. #3
    Trail Cubist
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    Quote Originally Posted by jeffscott
    Try to brake with short stabs rather than feathering the brake all the way down the hill.
    Good advice, I'll work on this. After I squirted water on the brakes last night they seemed fine...but I should probably inspect the rotors and pads.

    Scott
    29er wheels are dangerous. They may cause you to go faster which can result in serious bodily injury. óJim311

  4. #4
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    Take your pads out and inspect them. If they look shiny, give them a light sanding. Also look to see if the friction material is cracked. Squirting water on them when they're smoking hot may not be a good idea as rapid cooling could cause the friction material to crack and your rotors to warp.

  5. #5
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    Quote Originally Posted by oldskoolbiker
    Take your pads out and inspect them. If they look shiny, give them a light sanding. Also look to see if the friction material is cracked. Squirting water on them when they're smoking hot may not be a good idea as rapid cooling could cause the friction material to crack.

    Yeah I don't squirt water on them either, I am afraid I might warp a rotor or something, they only take a few minutes to cool on there own anyway.

  6. #6
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    What kind of brakes and rotor size?

    New riders tend to hold onto the brakes to avoid overrunning them before the skills develop. Speed tends to be more skill demanding, and that only comes with experience, even going down a simple fireroad descent.

    Don't spray water on your brakes, and don't touch them when hot. Just like a car.

  7. #7
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    Doh. Didn't even think of possible damage from squirting water on 'em. (It was really cool to watch it sizzle though, LOL) I'm sure the rotors are fine since they'd probably pulsate if they warped...but I'll definitely inspect the pads.

    Scott
    29er wheels are dangerous. They may cause you to go faster which can result in serious bodily injury. óJim311

  8. #8
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    Quote Originally Posted by SWriverstone
    Doh. Didn't even think of possible damage from squirting water on 'em. (It was really cool to watch it sizzle though, LOL) I'm sure the rotors are fine since they'd probably pulsate if they warped...but I'll definitely inspect the pads.

    Scott
    Not necessarily.

  9. #9
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    Quote Originally Posted by junktrunk
    What kind of brakes and rotor size?

    New riders tend to hold onto the brakes to avoid overrunning them before the skills develop. Speed tends to be more skill demanding, and that only comes with experience, even going down a simple fireroad descent.

    Don't spray water on your brakes, and don't touch them when hot. Just like a car.
    Avid Elixir R's, 185 front, 160 rear.

    As for brake usage...I'm not a total noob, but would consider myself a solid intermediate rider. To have used any less braking on this particular steep, rocky descent would mean I'd build up way too much speed very quickly and likely crashed hard. (So if I want to avoid smoking my brakes, maybe I should just stay off trails like this? But then how do you learn?)

    I was also on a 29er with tires at 40psi. (So we're talking FAST for a mountain bike!)

    Scott
    29er wheels are dangerous. They may cause you to go faster which can result in serious bodily injury. óJim311

  10. #10
    I Tried Them ALL... Moderator
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    DoT 4/5 = A lot

    Mineral Oil = Better feather them brakes, or risk no brakes
    "The mind will quit....well before the body does"

  11. #11
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    I've seen a guys leg who branded himself with the rotor when he leaned against it after a long downhill. Looked painful

  12. #12
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    I've had my brake pads on fire coming down a volcano in Tenerife....

    DG

  13. #13
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    Next time downshift down the hill, that will save your brakes.


    j/k

    I've smoke Shimanos before and I would not do it again.

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