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  1. #1
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    New to Disc Brakes - Overheating Question

    Hey guys,

    So, I just came out of the early '90s and bought a new bike with mechanical disc brakes. I must say, I love them! I'm 250lbs right now (which is why I'm riding again... Hah! Gotta get that number doooown!), and I feel like the stopping power is much greater than I had with my old V's.

    However, on my commute home there is a trail that drops me down about 200meters to the bottom of a little canyon and then back up again. It's a steep, rocky and loose little trail with some really tight switchbacks and a decent drop off of the edge. Needless to say, being that I'm just getting back into biking, it's a bit nerve racking right now as I build up my control and technique.

    Yesterday, however, my brakes got really hot... Like I could smell them!!! (No, I didn't touch them to see... hah! I did that once already by accident trying to get the front wheel off, so I now have a VERY healthy respect for those darn rotors). I'm thinking this can't be good, right? Or is it normal? The bike was just entry level (Cannondale C02 F8) with 160mm rotors (Tektro I think?). And, like I mentioned, I'm 250lbs so I'm asking alot of these things!

    So, my question is this. If they are overheating on this hill too much, will I be losing braking power? In other words, am I going to come up to one of those tight switchbacks and just keep on going...??? Also, with this heat I would think I also would have to worry about warping too, right? Is there something I can do differently to avoid this? Yesterday I was trying a new on/off technique (instead of just holding the brakes the whole way), which simply resulted in heavier braking when needed, so maybe this attributed to the overheating as well...

  2. #2
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    Quote Originally Posted by csmac2004
    Hey guys,


    So, my question is this. If they are overheating on this hill too much, will I be losing braking power?Yup if the get too hot you will get brake fade In other words, am I going to come up to one of those tight switchbacks and just keep on going...??? Well it has been okay so far right Also, with this heat I would think I also would have to worry about warping too, right? Is there something I can do differently to avoid this? Yesterday I was trying a new on/off technique (instead of just holding the brakes the whole way), which simply resulted in heavier braking when needed, so maybe this attributed to the overheating as well...
    Generally if you apply off and on braking you will get less brake fade than if you feather them all the time. Practice.

    Rotors don't seem to warp much from overheating...I have had mine blue hot and smoking with no warpage.

    However you can get a "glaze" building up on the rotors that makes the brakes much less effective...

    Take a little fine grained sand paper and pinch the rotor with it while you rotate the wheel, for a couple of minutes. that is usually enough to break the glaze.

  3. #3
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    Thanks for the tip about the sand paper. I did that on my rims with the V-Brakes, so I guess I should've thought of that...

    I will continue to practice the feathering technique though, thanks!

  4. #4
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    Not sure what trail you riding but

    When i weighed 165lbs I would absolutely smoke my brakes with a 160mm rotors. I use 180mm on my lite trail bike and 200mm on my AM bike. At 250lbs you are probably the upper end of 160mm rotors.

  5. #5
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    I'm heavy like you and moved up to a 185mm front rotor after getting a 160mm too hot for my liking. The larger rotor dissipates the heat better.

  6. #6
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    Thanks, guys! I was checking out some 180mm rotors for prices yesterday as that is the largest my front shock will allow (so it says), so I will go that route as well then. Thanks for the info!

    I rode downtown yesterday and got on a long, steep downhill (paved street) where I hit 75kph (46.6mph)... And then trying to stop at the bottom became an issue because of the heat... They were smoking then!!! And the braking power was seriously reduced, probably due to the glaze as was mentioned. I did sand the rotors lightly last night and they're good and grabby again today.

    So, yeah, better techinique is obviously needed, lose some weight (me, not the bike yet although that is in my plans as well) and bigger rotor. Thanks, guys!

  7. #7
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    Make sure you get the adapter to reposition your caliper for the larger rotor when you order it.

    Definitely work on pulsing the brakes instead of using one constant pressure, it will keep things much cooler.

  8. #8
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    Yeah, I was just reading about that (as I was trying to figure out how RST figured I could accommodate a bigger rotor), so that's really good to know now rather than when I'm trying to install it, hah!

  9. #9
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    Quote Originally Posted by csmac2004
    I rode downtown yesterday and got on a long, steep downhill (paved street) where I hit 75kph (46.6mph)... And then trying to stop at the bottom became an issue because of the heat... They were smoking then!!! And the braking power was seriously reduced, probably due to the glaze as was mentioned. I did sand the rotors lightly last night and they're good and grabby again today.
    A disc brake that's been heated up to smoking temperatures will almost certainly loose braking power, brake fade. This does however not mean that the pads are glazed over after this, brake power will normally return to normal when the brakes cool down. Reading that you sanded the rotor it seems to me that you experienced brake fade (which is temporary during overheating) and not glazed pads, because it is not the rotors that glaze over but the pads (and thus sanding of the pads and not the rotors is required when dealing with glazed pads).

  10. #10
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    not glazed pads, because it is not the rotors that glaze over but the pads
    Ok, that's interesting! Well, then all my sanding did was get rid of the black and blue color and turned them back to metallic again... Thanks!

  11. #11
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    Quote Originally Posted by csmac2004
    Thanks, guys! I was checking out some 180mm rotors...
    Skip this unnecessary step and and go directly to 203mm rotors. The fork should be fine, and as a 220lb fella myself I can tell you, that difference is noticable...

    Actually I am eyeing 220mm rotors for my DH rig.

  12. #12
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    Quote Originally Posted by uzurpator
    Skip this unnecessary step and and go directly to 203mm rotors. The fork should be fine, and as a 220lb fella myself I can tell you, that difference is noticable....
    Is this just a matter of a bigger adapter then? I would love to go even bigger than 180mm if I could. I was talking with my bike shop about this, so I will ask them more then when I go down there.

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    Ok, I did a bit more digging and I see that this is a well debated topic, so I do not mean to start up another one here. Thanks for the input, and I will keep researching this to see how large I can go on the rotor size.

  14. #14
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    +2 for skipping the 185 and just go with the 203mm. I'm running 203 front and rear and I'm extremely happy with them. No worries about premature lockup or modulation. In fact they seem to have better modulation.

    At 250lbs, even the 185 rotors will get too hot. I'm about 250 with full gear.
    '08 Hardrock HRXC
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    '14 Trance SX - 1x11 XX1/X01, Monarch Plus, Zee 4 pots, 203 Icetech, Laser V

  15. #15
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    Sintered pads might help too, they work better when hot.

    However they transfer more heat to the callipers, this can boil brake fluid, but you are mechanical.

    As long as the calipers are well made sintered pads could help you out a lot.

    +3 on 203mm rotors, I have even run 225mm rotors.

  16. #16
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    I use alternate braking mostly on those steep hills.

    But not in a "few seconds - on, few seconds - off" format.
    That heats up the brake a lot and it doesn't cool much in the "off" period.
    You also build up a lot of speed in the "off" moments.

    It's more like "tap dancing on the levers" i.e. quick "on and off" and alternating front to rear if possible.

    It takes a little practice, a gentle touch and one needs care cornering using this (maybe leave this bit until later).

    But it works well. I don't ride at that weight but ride steep long hills.

    I find it better than other methods I've used.

  17. #17
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    Too bad there is no chart that correlates weight with rotor diameter. I am 200lbs dry (TMI!) and I just smoked my rotors for the first time yesterday. I was coming down, slowly, from about 1,500 feet up and on the last stretch I whipped up to 40 km/h and when I braked to come to a stop on the downhill I could smell my brakes. The caliper was quite warm.

    That was the first time I smelled smoke. Also, there was a little darker discoloration and everything was pretty hot.

    It is an AM bike and I have Elixir 9 Trail brakes, sintered pads and 180m front and 160mm back. I try to make sure the braking is balance front/back.

    Should I get bigger rotors (200/180 combo)? Or maybe this was a one-off instance due to long descent and heating? Or maybe a lesson to stop partway and let everything cool.

    I guess what worries me a bit, the road continued down quite a bit 1 km more descending and if I braked most of he way down things might have been even hotter. We have quite a few long descents here on the roads, some over 3000 feet, and I cannot imagine having to wonder if I am ruining my brakes.

    Should'nt I be able to descend the entire way with the brakes on lightly to control my speed without worrying about burning them? I thought that was a car problem in the 1960's when American 5 ton cars would need to stop and cool their brakes on mountain highways...

  18. #18
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    Quote Originally Posted by TracksFromHell View Post
    I try to make sure the braking is balance front/back.

    Should I get bigger rotors (200/180 combo)? Or maybe this was a one-off instance due to long descent and heating? Or maybe a lesson to stop partway and let everything cool.

    I guess what worries me a bit, the road continued down quite a bit 1 km more descending and if I braked most of he way down things might have been even hotter. We have quite a few long descents here on the roads, some over 3000 feet, and I cannot imagine having to wonder if I am ruining my brakes.

    Should'nt I be able to descend the entire way with the brakes on lightly to control my speed without worrying about burning them? I thought that was a car problem in the 1960's when American 5 ton cars would need to stop and cool their brakes on mountain highways...
    Basically no! bike brakes are built far lighter for their duty than car brakes.

    Bike brakes will overheat if you "drag " them lightly (or heavily) down long hills.

    You need to perfect the stabbing techique. That is brake hard then let the brake off. then stabb again to control your speed. You can do sexy things like stab the front then the back to immitate dragging brakes.

    This allows alot more air flow to the pad surface and keeps the brake much cooler.

    If you are stabbing the brakes and you still over heat then it is time for a bigger rotor.

    I went down Mouna Kea...hit about 75 kph. Grabbed for the brakes and both over heated quickly. (think it is 15% grade). Then the brake power fadded right off, and I was still accelerating. So I started stabbing the brakes...voila got it all stopped in about 300 yards.

  19. #19
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    I'll try that. I cannot see myself braking down long hills anymore if I can avoid it. I rather like my own lack of aerodynamics to slow me down and it is a lot more fun going fast!

    Was looking at the finned XTR style pads available for Elixirs. Has anyone tried the pinned koolstop pads? That might be an idea that works better than a rotor size upgrade for heat management??

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