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  1. #1
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    2020 Update: Can hydraulic brakes overheat?

    Okay I know this question has been beat to death a lot. I did several searches on brakes overheating and everything I came up with is many years old. So I'm starting this thread as an UPDATE with a focus on CURRENT (as of 2020) hydraulic braking systems.

    What got me thinking about this was a ride yesterday, which presented what I believe is the "ultimate braking nightmare" scenario:

    Seeking a good workout, I did a gravel ride up a road in a national forest. I climbed about 3500 feet in 4-5 miles, and the gradient was continuous (zero flat spots or change in gradient whatsoever). It was uphill ALL the way.

    So flip that to riding down: remember, 4-5 miles, ALL downhill for 3500 feet, and (here's the kicker) the entire road—all the way down—was covered in fine pea gravel with lots of "coarse gravel sand" thrown in.

    Translated, this meant no "stabbing" the brakes—because the second you stab, you start sliding uncontrollably. (Even if you thrust your weight downward for more traction.)

    So I basically dragged the brakes pretty much all the way down the mountain. I tried letting off on them as often as I could, but I weigh 220lbs—and the second I'd let off the brakes I'd accelerate almost instantly to terminal velocity, LOL.

    I basically had two choices: drag the brakes for 5 miles down the mountain, or just stop every so often and let the brakes sit and cool off for a few minutes (which I didn't really want to do). I was worried all the way down that my brakes would overheat and/or I'd damage them somehow. (By the way, I have SRAM hydraulic brakes with 180mm rotors on my XC bike.)

    What I'm wondering now is, should I have been worried at all? Or are modern hydraulic brakes and 180mm rotors perfectly happy to provide undiminished stopping power when dragged for 5 miles down a mountain more-or-less nonstop?

    No, my brakes didn't explode or stop working...so that might be my answer. I guess I'm really wondering more about engineered intent and limitations—are they designed for that kind of abuse?
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    Yes they are designed for extended braking sessions. But just because you didn't run into any performance issues doesn't mean someone else will as well.

    You've got 180mm rotors that's good, larger rotors dissipate heat better than smaller.

    You've probably got light weight wheels & tires, also good.

    Overall performance depends on a lot of things, if you experience fad or a mushy lever, might be time for bigger rotors, metallic pads or a fresh bleed. Lots of factors come into play.

    Should you have been worried? Not really, catastrophic brake failure is pretty uncommon. On independent braking systems almost unheard of. Brakes usually start fading (requires more lever pressure) or get spongy (brake levers pull farther back). Neither will kill your ride, but they will let you know something needs attention.
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  3. #3
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    It depends. The simple answer is no, they will build up heat to the point where the braking power will diminish. Will you encounter this kind of slope?

    There are some awesome alpine hike-a-bikes that I do around here that have extended 45% grades and long sections just a bit flatter than that. They heat brakes up like crazy and you don't really ever get much of a chance to let them "cool down", unless you stop. It then depends on your brakes and technique. It is definitely possible to glaze the rotors over and boil (contaminated) fluid in those conditions, leaving you with diminished braking.

    And to add to the above, not just bigger rotors, but rotors with more metal, whether it be fins or whatever, that helps dissipate heat too.

    It depends a lot on the trail, if there are a lot of grade reversals, where braking is more acute, rather than extended. You can even smell burnt brakes if you are pushing it too hard. It's based on what you experience. Generally, doing something that starts to overheat 180 brakes on an XC bike is not a great idea, rather than upgrade the brakes, it's better to get the correct bike for that kind of riding, as anything that requires 203mm rotors on an XC bike means you are pushing that XC bike way beyond "XC".
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    Back in the day I used to get my 140mm rotors glowing a dull red at night on a 2400' descent I regularly did. Used those same brakes (Juicy 7) for years except for pad changes.
    What, me worry?

  5. #5
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    Fluid fade is very unlikely. Usually when someone experiences brake fade it's due to the pads overheating, which is a legit issue when riding DH. Better pads and bigger rotors help.

  6. #6
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    Thanks all—it's good to know I'm not likely to experience catastrophic brake failure on a long descent. :-)

    Quote Originally Posted by Jayem
    Generally, doing something that starts to overheat 180 brakes on an XC bike is not a great idea, rather than upgrade the brakes, it's better to get the correct bike for that kind of riding, as anything that requires 203mm rotors on an XC bike means you are pushing that XC bike way beyond "XC".
    This makes sense, except in my case: I'm using an XC bike to do long rides on unpaved forest roads in extremely mountainous terrain, with very little singletrack. This seems to me to be exactly the kind of ride you'd be better off on an XC bike (sorry, but gravel bikes suck for riding on gravel, LOL). Except for the loooooong descents (on gravel).

    So maybe for this kind of riding bigger rotors (203mm) might be useful?

    Scott
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  7. #7
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    Get a dropper post; if you brakes fail, you can drop the saddle, put down your feet, and Flintstone it.

  8. #8
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    Quote Originally Posted by Jayem View Post
    It depends. The simple answer is no, they will build up heat to the point where the braking power will diminish. Will you encounter this kind of slope?
    Dammit, I meant to say "yes". I was looking at something in the post and not the title.
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    I'd go 200 or 203 up front, Down hills you'll be putting more stress on that front rotor. Due to your weight being pushed farther forward your front brake is going to have a lot more potential to slow you down since the rear tire is relatively unweighted.
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    The brakes will reach a point where you can keep squeezing the lever, but not getting much (if any) braking power out of them, due to overheating. I've never had it happen with 180mm rotors, but I, and other buddies have had it happen with 160mm rotors.

    And there was a thread here recently about someones brakes failing in a similar scenario to what you're describing.

    At your weight, I'd be going big rotors, and metallic pads, unless you're really worried about bike weight. Because, objectively, you did survive the descent without brakes failing, which is really the only thing that matters.

  11. #11
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    The prevailing wisdom has always been: focus on the front brakes. This article suggests that's all wrong, and makes an argument for going with a larger rotor in the rear.
    https://enduro-mtb.com/en/rotor-size-myth/

    They say "But, if you weigh upwards of 80 kg and often tackle descents of several hundred metres or more, you should take a closer look at the colour of your rotors. In almost all cases, it’s the rear rotor that takes the brunt of the braking, overheating and discolouring after cooling down. In contrast, the front disc usually retains its normal silver colour."

    They further point out that many times you'll be braking less in front (to keep the front wheel rolling and maneuverable) while you'll tend to drag the rear brake more.

    So apparently many enduro riders recommend using a larger rotor (with metallic pads) in the rear, smaller rotor with organic pads in front.

    Thoughts?
    Scott
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    I guess it depends on how you brake. I don't tend to drag rear brakes and rarely overheat them but I'm running 203mm icetech's front and rear. Last time I noticed a brake overheating was a rear 160mm.

    I only run metallic pads, organics just don't last in the wet pnw winters.

    But if I were a racer still not sure I'd go with a larger rear rotor compared to the front. It could be awesome but I've never done it, and it seams backwards to me. I can't argue with a 203 out back but not combined with a smaller rotor up front. For me that's where I get most of my stopping power.

    It sounds like the author of that article was running 220mm rotors front and back but found the 220 up front was a bit overpowered and was causing modulation issues. That's why he downsized the front to a 200mm. So that's 1 guy. I don't want to start hunting down rotor sizes for EWS athletes but I'd guess those running larger rear rotors would be the exception rather than the rule. That's if there are any at all.
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    The vast majority of gravity riders use the same size rotors front and rear. If you're dragging brakes down the mountain then yeah you're almost certainly putting more heat into the rear rotor. In that case I'd go same size rotors front and rear. If you were using more front brake then I'd go same size rotors front and rear. In other words, I'd go same size rotors until it's not longer a theoretical issue.

    If you're worried, go bigger front and rear and get the best metallic/sintered pads you can find.


    Btw, Myriam Nicole is running a larger rear rotor but that maybe because the new Commencal frame uses 220mm direct mount.

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    I think thats a really interesting article, and one that I think I at least partially agree with. I'm at the very least on team "larger is better if you're heavy, and probably at least equal size front and rear".

    Most of the time, the prevailing wisdom/comments have been that the front does more braking force, because of weight transfer. And that larger rotors on the rear "waste" their potential, because they will lock up before they can ever utilize the additional stopping power the larger rotors provide. This is absolutely true.

    What the article points out though, is that larger rotors provide BOTH, more power, AND more cooling/heat capacity. And since braking with the front can be dangerous at times (loss of control), you're much more likely to do softer, more continuous braking with the rear. And that constant application of brakes is what leads to the overheating.

    Annecdotal evidence:

    The only rotors I've ever seen overheated have been rear brakes. And the only brakes I've ever had (or had friends who have had), have also been rear brakes.

    My theory is that brakes with high amounts of modulation, pair better with larger disks, particularly in the rear. IE, if you have lots of modulation, and a bit powerful rotor, you can still manage to not lock up the rear brake. It will be harder to do the same thing with a "light switch" modulation rear brake.

    I'm 6'1", and around 190-200lbs geared up.

    I recently upgraded from a 180mm rear rotor, to a 203mm rear rotor. My front rotor is a 200mm. My front pads are semi-metallic, and my rears are now full metallic. So I guess I'm testing out their theory, even though my rear rotor is only 3mm larger than the front (I was mostly looking for even sizes front and back, and found a good deal on a 203...).

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    Here's a discussion from the pits

    https://youtu.be/ieeV3pLSoVo
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  16. #16
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    I still don't see the point of using a small rotor up front and a big one in back.

    If you're doing the kind of riding that warrants a 203 (or a 220) rotor in the back for heat dissipation, you're also doing the kind of riding where you could well make use of the same-sized rotor up front. Not that you'd need that power all the time, but for the typical rider riding on open, public trails (we're not talking about closed pro race courses here), you need to be able to emergency stop. Rear-only isn't going to pull that off, and putting a little rotor up front isn't really going to cut it.

    Just run same size rotors. There is no legitimate reason not to.

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    Quote Originally Posted by SWriverstone View Post
    Translated, this meant no "stabbing" the brakes—because the second you stab, you start sliding uncontrollably. (Even if you thrust your weight downward for more traction.)
    FWIW, stabbing is a really bad word to use for this. It's really more of a gentler pulsing. Brakes with a broader modulation band are a little easier to do this with than those with a tighter modulation (ahem - shimano - ahem), but it's doable on any brake. It just requires finer muscle control the narrower the modulation band is.

    I pulse my brakes down quite a few sketchy descents without any problems. It's real interesting when doing it on my skinny tire Salsa Vaya on a long, soft gravel descent where the front tire is sinking and wallowing all over the damn place regardless of what you do with the front brake.

  18. #18
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    Quote Originally Posted by Harold View Post
    I still don't see the point of using a small rotor up front and a big one in back.

    If you're doing the kind of riding that warrants a 203 (or a 220) rotor in the back for heat dissipation, you're also doing the kind of riding where you could well make use of the same-sized rotor up front. Not that you'd need that power all the time, but for the typical rider riding on open, public trails (we're not talking about closed pro race courses here), you need to be able to emergency stop. Rear-only isn't going to pull that off, and putting a little rotor up front isn't really going to cut it.

    Just run same size rotors. There is no legitimate reason not to.
    Maybe its just how we're describing it, but I don't think anyone is recommending a "small" rotor up front (like a 140/160, or even 180).

    I think its just that if you're already running large rotors, and are still cooking the rear brake.

    Again, maybe its just me/my buddies, but I've never seen a front brake that was overheated, its always been the rears.

    And by the same token, with proper DH brakes, and 200/203mm rotors, I've not heard many people complain about lack of power for the front, and the article was suggesting that maybe a 220/223mm front rotor was too powerful for most mere mortals.

    Its really just heat management, at least from what I can understand. But I can see there is some logicto it, even though I've not tried it yet.

    Like I said, I just went from a 180mm rotor to 203mm rotor in the rear on my bike. So now I've got the "same" size rotors front and rear. Maybe in the future I'll test out something different.

  19. #19
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    Id look at same size rotor but with the aluminum centers, they will be lighter and run cooler. There is one sram model and a similar shimano model that work great and also drop weight.

    https://bike.shimano.com/en-EU/produ.../RT-MT900.html


    you can run into problems upsizing, some forks arent recommended for the larger sizes.

  20. #20
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    Quote Originally Posted by Harold View Post
    I still don't see the point of using a small rotor up front and a big one in back.

    If you're doing the kind of riding that warrants a 203 (or a 220) rotor in the back for heat dissipation, you're also doing the kind of riding where you could well make use of the same-sized rotor up front. Not that you'd need that power all the time, but for the typical rider riding on open, public trails (we're not talking about closed pro race courses here), you need to be able to emergency stop. Rear-only isn't going to pull that off, and putting a little rotor up front isn't really going to cut it.

    Just run same size rotors. There is no legitimate reason not to.
    I agree, that's the main flaw in this line of thinking. I totally get that you may be heating up the rear more with the brake feathering on such descents, but on those exact descents, you need some mega front power so you can slow down enough and be able to let off the front brake or both brakes for enough time to let them cool. A lot of riders never really experience this much, I was surprised how little it applied on our local built flow and tech trails. I'm braking, but damn not much, fairly infrequent. Then put me one one of the big hike-a-bikes I do to come down the side of a mountain where there can be extended 45% grade slopes. The brakes heat up like crazy, I need a lot of heat capacity and power out of the front, in addition to heat capacity in the rear. Or park riding on any of the steeper tech trails. Typically, you are using some heavy extended braking there, vs. the more acute on/off braking on lesser stuff. I still don't see why you'd want a bigger rear rotor, only that you might want equal heat capacity. In 2020, there are a few other ways to do this too, like Hope vented rotors on the V-series brakes, or thicker rotors like TRP uses (more metal=more cooling). The classic way is equal size front and rear rotors, but bigger rear rotor than the front? I'm with you, in any of those situations I'd likely need even more front power and heat capacity. Recently switched to Hope V4 front and E4 rear, same size 203 rotors.
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  21. #21
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    [QUOTE=SWriverstone;14964821They say "But, if you weigh upwards of 80 kg and often tackle descents of several hundred metres or more, you should take a closer look at the colour of your rotors. In almost all cases, it’s the rear rotor that takes the brunt of the braking, overheating and discolouring after cooling down. In contrast, the front disc usually retains its normal silver colour."[/QUOTE]

    I've seen this myself (rear discoloring/fading on long braking descents with the front not experiencing this). My opinion, as a rider that tries to use front/rear brakes as evenly as appropriate, is the rear isn't taking more brunt, as much as it is working harder due to being a smaller diameter than the larger front to do the same amount of work.
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    I think the rear fade/discoloring problem comes from how the brakes are generally used. Front brake is used when you want to really slow down the speed, while rear brake is used more to control the bike and speed. So on this kind of long moderately steep tech descents you generally don't need to be constantly trying to slow down, but you want to just control the speed and that is easier by constantly dragging the rear brake, while front brake is mainly used on situations when speed starts increasing(no grip on rear, slope gets suddenly steeper) or if you want to slow down for some reason(small sketchy drop or other techy section).

    Technically one can also drag with front brake too, but that tends to have negative effect on steering and controlling the bike. So if one is riding long, steady pitch downhill section where you need to brake and actively "steer" and control the bike, it is likely that rider "drops the anchor" and drags the rear brake whole time, while front brake is used only on certain parts to slow down the speed. So this analogy would strongly support idea of having rear rotor same size or even bigger than front. That isn't common, but there should not be reason why you could not put rear rotor bigger than front, if this kind of scenario is something you do often...

    Bigger rotor diameter helps braking by having longer "lever", hence more braking force with same "finger pressure", and via added surface area it heats up slower and cools faster than smaller disc. Thicker rotor helps mainly because of the added mass, so it takes more energy to heat up the disc. Surface area isn't increased that much, so heat dissipation does not improve that much.


    When it comes to "boiling" brakes, I believe this kind of dragging the brakes long time with high speed is the worst situation; friction is adding heat to the system all the time, while the disc, pads and caliper has no time cool down, so the heat just builds up. If the system builds up enough heat to exceed boiling point of the fluid(on atmospheric pressure), this doesn't mean problem yet, as long as you drag the brake. While brake is applied it creates pressure to the brake fluid and increased pressure increases also boiling point. So problem might appear if you release the lever => pressure drops > fluid boils and increased volume pushes fluid towards the reservoir => when you press lever again, the fluid is in the reservoir and there will be only gas bubbles in the hose/caliper ==> no braking power.

    Another problem point might come if you keep dragging the brakes even further much beyond the boiling point, as long as brake is applied, the pressure keeps fluid from boiling and head adds up. I would guess the caliper seals are the first place to give when just adding heat to the system. Or it might be the hose that melts or something else, but this is highly unlikely to happen...

    I have only once managed to boil my old Avid Juicys, and only rarely heard same happening. And I've never heard anyone melting caliper seals or brake hose or otherwise destroyed brakes by overheating...

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    I'm pretty sure you're going to exceed the pad's operating temperature before you boil the fluid assuming you're fluid is in decent condition.

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    Quote Originally Posted by Jayem View Post
    It depends. The simple answer is no, they will build up heat to the point where the braking power will diminish. Will you encounter this kind of slope?

    There are some awesome alpine hike-a-bikes that I do around here that have extended 45% grades and long sections just a bit flatter than that. They heat brakes up like crazy and you don't really ever get much of a chance to let them "cool down", unless you stop. It then depends on your brakes and technique. It is definitely possible to glaze the rotors over and boil (contaminated) fluid in those conditions, leaving you with diminished braking.

    And to add to the above, not just bigger rotors, but rotors with more metal, whether it be fins or whatever, that helps dissipate heat too.

    It depends a lot on the trail, if there are a lot of grade reversals, where braking is more acute, rather than extended. You can even smell burnt brakes if you are pushing it too hard. It's based on what you experience. Generally, doing something that starts to overheat 180 brakes on an XC bike is not a great idea, rather than upgrade the brakes, it's better to get the correct bike for that kind of riding, as anything that requires 203mm rotors on an XC bike means you are pushing that XC bike way beyond "XC".
    Of the local descents near me, the ones hardest on brakes involve dozens of spots where you're naturally pulsing the brakes. Ideally you're skilled enough to be able to let off the brakes entirely and only brake when you approach the technical spots. The drops or the rocky switchbacks or the chundery rock gardens or whatever the case may be. If you're not that skilled (or that fearless) which often enough, I'm not, then you're not letting off the brakes very much at all to let them cool. I don't think you're going to be cooking fluid under much of any scenarios, but you'll definitely get them warm enough for pad fade.

    Shimano 2 pots with 180mm rotors and metal pads had very insufficient cooling for me and I experienced hand cramping (due to squeezing the levers so hard) so much that I've had to stop and give myself multiple breaks. Bumping the front to a 203 helped, but I was still flirting with the limits. Braking was barely sufficient, but I felt like I had almost no safety margin if I needed to make an emergency stop due to a downed tree around a sharp corner, a rider down ahead of me, hikers coming up, or whatever. Not sure going to a 203 rear would have helped enough. Would have only been a little bit, I think. Went with Hayes Dominion A4's as the next brake option (still metallic pads, and are an example of a brake with thicker rotors to aid in heat management), and found improvements all around in overall power, modulation, as well as heat management. Namely, my hands don't cramp up because the finger inputs needed are so light on these brakes.

    I still don't really drag the rear brake. My concerns are more about evening out power delivery of the brakes to the wheels such that I maintain traction, keep my speed within my comfort zone, and have the ability to stop when I need. So a 180 in the rear works for me. I don't heat up and discolor the rear rotor. I apply the brakes at pretty much the same time, though I vary the pressure on each depending on the situation. Even on the fast, flowy descents in the area, I'm more of an "apply the brakes when needed and let off of them completely when not needed" sort of rider.

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    Quote Originally Posted by jeremy3220 View Post
    I'm pretty sure you're going to exceed the pad's operating temperature before you boil the fluid assuming you're fluid is in decent condition.
    Yep, this might be the case too, although I'm not sure what kind of temperatures the pad material or its ability to slow down starts to deteriorate. Likely metallic sintered pads can withstand more heat than organic resin pads. Pads likely won't melt or anything, as quite commonly used procedure to "clean" contaminated pads is to heat those with torch or similar to high enough temp to evaporate/burn all oil residues and the pads work just fine after that...

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    Quote Originally Posted by Verttii View Post
    Yep, this might be the case too, although I'm not sure what kind of temperatures the pad material or its ability to slow down starts to deteriorate. Likely metallic sintered pads can withstand more heat than organic resin pads. Pads likely won't melt or anything, as quite commonly used procedure to "clean" contaminated pads is to heat those with torch or similar to high enough temp to evaporate/burn all oil residues and the pads work just fine after that...
    Yeah they don't melt, the friction coefficient just starts dropping off at a certain temperature. It's hard to make materials that have a hugely broad range where they operate at the desired friction coefficient.

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    In my "use case" (riding down a pea-gravel-covered forest road that's downhill 100% of the way for 4 miles and 3500'), I kept alternating between gently applying both front/rear brakes in a 2-3secs on/2-3secs off cycle...and dragging the front brake only for a few seconds, then dragging the rear brake only for a few seconds.

    I couldn't tell which technique was better—they both seemed about identical. <shrug>

    Scott
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    2020 Update: Can hydraulic brakes overheat?-be864a3b-c88d-4ca2-9c58-345fc7c75ca0.jpg

    Mine are getting so hot they go discoloured.

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    Quote Originally Posted by SWriverstone View Post
    In my "use case" (riding down a pea-gravel-covered forest road that's downhill 100% of the way for 4 miles and 3500'), I kept alternating between gently applying both front/rear brakes in a 2-3secs on/2-3secs off cycle...and dragging the front brake only for a few seconds, then dragging the rear brake only for a few seconds.

    I couldn't tell which technique was better—they both seemed about identical. <shrug>

    Scott
    We have a lot of logging roads like that. Those roads can really be hell on brakes. I can certainly see where big rotors and strong, 4-piston brakes would help.
    Riding Washington State singletrack since 1986

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    The non dominant hand (the left hand for most people) exerts less finer control on feathering and braking - I am wondering if this is the reason why riders are reluctant to put bigger rotors at the front and use it but instead opt for big rotors at the back because it is on their dominant hand.

  31. #31
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    Would thicker 2.1 rotors at the same size vs 1.8/1.9 rotors help? Something like a Magura Storm(comes in various sizes) or Magura MDR-P Rotor(only comes in 200mm & 220mm sizes).

  32. #32
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    Quote Originally Posted by Funoutside View Post
    Would thicker 2.1 rotors at the same size vs 1.8/1.9 rotors help? Something like a Magura Storm(comes in various sizes) or Magura MDR-P Rotor(only comes in 200mm & 220mm sizes).
    Probably helps a little, but not too much. Increasing thickness of the rotor mainly increases its volume(=mass), but increase of surface area isn't that big. End result should be that it will take more energy to heat up the disc, but the capability to radiate heat off does not improve much as that is relative to surface area.

    To increase surface area to better radiate/conduct heat out from the disc, the easiest way is to increase rotor size. If this is not option, for whatever reason, one way is to take rotor which has wider "arms" between the center and outer braking surface, so that heat conducts better to the inner part of the disc. Another way used by Shimano is to use sandwich structure, where braking surfaces are stainless steel as on normal disc, but with aluminium layer in the middle which conducts heat much better than stainless steel. In addition to that for even more efficient is to have some kind of "cooling fin" on the inside of the disc, like on the Shimano Freeza rotors have...

  33. #33
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    Had my first time of really cooking my brakes during yesterday's ride.

    To put things in perspective...


    We had done around 4000m of climbing (unsure of elevation) and two 1km DH runs (not overly steep) up and down flow w/ a bit of jank for good measure.

    Then a 500m dh, a little steeper w/ more flow and loads of flat corners.

    The next DH run was around 1km long and got pretty steep for the bottom third.

    Anyway, about halfway down this run my brakes started howling and w/ about 250m to go, they weren't doing much slowing down.

    At the end, I could smell my rotors and the levers were almost coming back to the handle bar.

    This is the first ride I've experienced such an issue.

    I've had Shimano single pot brakes fade towards the end of a sustained 750m DH.

    I've since cleaned the rotors with alcohol and swapped out brake pads.

    I've also up'ed the rear rotor size from 180 to 200.

    The bike is a 160mm travel 29er and I'm a 240lb Clyde.

    The brakes are Tektro Orion 4 pot brakes. I always run Sintered pads. On the day in question, I had Shimano Saint pads in...

    They are a decent substitute, for the real thing.

    NB, I've found going from 200mm rotor to 203mm rotor on my AM HT 29er has made a positive increase in braking performance.

    Maybe I need 220's up front and 200's outback on all my mules?

    Sent from my HD1900 using Tapatalk
    "Mountain biking: the under-rated and drug-free antidepressant"

  34. #34
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    Quote Originally Posted by Verttii View Post
    Probably helps a little, but not too much. Increasing thickness of the rotor mainly increases its volume(=mass), but increase of surface area isn't that big. End result should be that it will take more energy to heat up the disc, but the capability to radiate heat off does not improve much as that is relative to surface area.

    To increase surface area to better radiate/conduct heat out from the disc, the easiest way is to increase rotor size. If this is not option, for whatever reason, one way is to take rotor which has wider "arms" between the center and outer braking surface, so that heat conducts better to the inner part of the disc. Another way used by Shimano is to use sandwich structure, where braking surfaces are stainless steel as on normal disc, but with aluminium layer in the middle which conducts heat much better than stainless steel. In addition to that for even more efficient is to have some kind of "cooling fin" on the inside of the disc, like on the Shimano Freeza rotors have...
    My gravel bike has 160mm centerlock rotors f+r(Ultegra/GRX) with cooling fins. I honestly can't tell if the fins are helping or not, but it does give me an extra sense of it will likely fail less in the 5-6 months of summer we have.

    Is there any downside to going to 2.0/2.1 thick rotor, beside possibly not fitting? Cause I've been thinking about putting the Maguras on my touring mtb. I take thicker rotors would be a hair harder to warp due to heat & just general riding, ie something hitting it on the trail?

  35. #35
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    Quote Originally Posted by Funoutside View Post
    My gravel bike has 160mm centerlock rotors f+r(Ultegra/GRX) with cooling fins. I honestly can't tell if the fins are helping or not, but it does give me an extra sense of it will likely fail less in the 5-6 months of summer we have.

    Is there any downside to going to 2.0/2.1 thick rotor, beside possibly not fitting? Cause I've been thinking about putting the Maguras on my touring mtb. I take thicker rotors would be a hair harder to warp due to heat & just general riding, ie something hitting it on the trail?
    Thats why some Ebike specific brakes have thicker rotors. They take longer to reach their heat capacity, and resist warping much more.

    Which is also why TRP's new DH brakes use thicker (DHR EVO uses 2.3mm) rotors.

    But you're right, the downside with brakes designed for 1.8mm thick rotors, is increased pad noise/drag, especially with fresh pads. With somewhat worn pads it shouldn't be an issue, but with fresh pads, it could be a real problem.

  36. #36
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    Quote Originally Posted by Funoutside View Post
    Would thicker 2.1 rotors at the same size vs 1.8/1.9 rotors help? Something like a Magura Storm(comes in various sizes) or Magura MDR-P Rotor(only comes in 200mm & 220mm sizes).
    I just got the Magura MDR-P. I measured it several times last night, it seems to be 1.95mm thick. I was hoping for a little thicker, but oh well.

    Performance wise, it did amazing. A couple days ago I took the bike down a trail that has an extended section of 30-40+% with a peak of 47 and it didn't blink an eye. This wasn't like a couple hundred feet section, it's more like a good quarter mile or more and while not nearly as bad as the bigger descent I did the weekend before with multiple sections even steeper, it's a good test and it was always beyond the control level of my shimano XT 2 pots with 8" rotors and sintered pads. The amount of control I had was great, never felt like the brakes were beginning to glaze or fade and I was able to use normal pressure, not death-clamp. Hope to do some more stuff like that soon, but the season is running out quick.

    Indications so far are that these will mange the heat well and make up for the Hope V4s lack of power (compared to other brakes with better MC/SC area ratio and leverage). I knew this getting into the Hopes and it was my intention to "over-rotor them to make up for it, seems to work just fine.

    Going back to the first post, IME it's the grade and the time you spend on that grade. In most cases, unless you have some giant runout and then a grade reversal or at least big flat area, you just can't sustain more than about 30% grade without heating the crap out of most brakes. You can do it down a short chute or for a short period of time, but whenever you have to spend a long time. Remembering back to my WA trip last year, Skyline put my brakes over the edge a little, whereas the harder trail Out of the Blue did not, but if I recall correctly, it had more grade reversals and I kept taking the "diamond" lines on Skyline. You can't just look a trail profile though, grade reversals are often too short to see on the overall profile and gradient, but on these rides where I know they exist, I'm seeing at least 30% for this threshold, at least with the 8" rotors and what I was using before. At our bike park, pretty much everything is steeper than 25% and it's a bloody steep mountain, so you get the same issues. But it's all a factor of grade and the time you spend on that grade IME. That's what overheats brakes. I'm not sure what the upper limit is, but at 50% my XTs massively overheated and glazed and the Hopes (with smaller rotors) just didn't bite enough. Both felt similar after 100 feet on the grade due to their diminished performance.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

    You're turning black metallic.

  37. #37
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    Quote Originally Posted by yeti rider View Post
    Click image for larger version. 

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    Mine are getting so hot they go discoloured.
    shit mine look like that also! do you clean it off? or how do you get rid of it
    2020 yeti sb165 t2

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