Hydraulics... how cold is too cold?- Mtbr.com
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  1. #1
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    Hydraulics... how cold is too cold?

    So I bundled up and hit my local mtb trail today. Probably low 20s (F) when I headed out, only in the mid-teens when I finished just after sundown. However, I slapped the knobby wheelset on my hardtail (linear-pull brakes) instead of riding the full-susp. While I was out, I started to wonder how well the Avid Juicy 5s on my full-susp would work in those temps. How low do temps have to be before hydraulic brakes can't handle it? Anybody out there have some thoughts/experiences?
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  2. #2
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    Low teens is not a problem for DOT fluid.
    When under pressure, your level of performance will sink to your level of preparation.

  3. #3
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    How about mineral oil?
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  4. #4
    local trails rider
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    Last winter I used Shimano LX hydros (mineral) for 2 hour rides at around -10 Celsius (around 15F): nothing unusual from the brakes.

  5. #5
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    iv been riding lx's in about 2 degree weather for the last couple days and am having problems with the pistons not retracting back into the caliper after i squeeze the brake lever.

  6. #6
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    While the fluids used in brakes work even in the coldest temperatures the brake system can suffer at least from following issues:
    - while riding in near freezing conditions the slush and water can freeze at caliper and prevent pistons from moving or retracting (can happen to any disc brake).
    - in very cold weather some calipers have had leaking problems as piston seals have shrinked due cold (happened to me with older Maguras, calipers leaked while storing the bike in -30C - fixed by Magura).
    - extremely contamined brake fluid can cause some trouble (trials jocks were using water in their brakes a couple of years ago).

    I don't think any of the above is a regular problems, at least when you compare that to frozen rims and canti/v-brakes.

  7. #7
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    Shimano brakes will start to leak below 10-15F, XTR seem to be the worst. In general, the DOT fluid brakes seem to handle the cold better than the mineral oil ones. My Formula K24s leaked at about 0F.
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  8. #8
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    I find that when it gets cold (below freezing) my XT 765 pistons don't retract properly leading to almost on-off, zero modulation braking with very tight levers. Usually have to reset the pistons post-ride to get them working properly again even after they warm up. Just part of winter riding I guess.

  9. #9
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    Quote Originally Posted by nanook93
    So I bundled up and hit my local mtb trail today. Probably low 20s (F) when I headed out, only in the mid-teens when I finished just after sundown. However, I slapped the knobby wheelset on my hardtail (linear-pull brakes) instead of riding the full-susp. While I was out, I started to wonder how well the Avid Juicy 5s on my full-susp would work in those temps. How low do temps have to be before hydraulic brakes can't handle it? Anybody out there have some thoughts/experiences?

    -35 C work fine, only problem is icing the disk, that happens at high humidity and low temps, can get exciting.

    XTR's

    Salt will build-up in the caliper and on the pads and screw things up.

  10. #10
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    good info!

    Thanks for sharing everybody. This is good stuff to know. I'm a bit of a noob when it comes to hydraulic brakes!
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  11. #11
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    im not sure how much heat is actually generated... but when I ride on extremely cold days I start out with some light brake pressure to "pre-heat" the caliper and fluid some. How much does it help? Not sure..... but it makes sense in my head and couldn't hurt to try
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  12. #12
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    Anyone had problems with Avid?
    My Juicy 3 starts leaking a bit below -5C, things get realy nasty below -15C.
    Then the lever goes straight to the handlebar. No oil pressure at all.
    I cleaned an refilled the system, no problems, until it starts freezing again...
    This is my front brake, my rear brake and my Juicy 5 seem untouched by he cold.
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  13. #13
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    I encountered non functional Hayes HFX 9 brakes during a race that started at about 19 F a couple of weeks ago. The first descent was an eye opener as the brakes simply didn't work without some serious coaxing. Every subsequent descent was the same. When the brakes did work, the lever had absolutely no throw. Kind of freaked me out.

    There were a couple of good sized water crossings on the ride. You get wet.

    These brakes run DOT3 fluid. First hydros I've ever owned. Lots of folks had similar experiences. Do you think this was a problem with the fluid, as in they need a bleed? The piston seals? Glazed up rotors? A combination of all?

    Makes me want to go back to BB7s, I'll tell you that.
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  14. #14
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    Quote Originally Posted by cbratt
    I find that when it gets cold (below freezing) my XT 765 pistons don't retract properly leading to almost on-off, zero modulation braking with very tight levers. Usually have to reset the pistons post-ride to get them working properly again even after they warm up. Just part of winter riding I guess.
    I finally had this happen with my SLX in -4F (-20°C). First 40 minutes were ok and nothing special but once I went through some hub deep snow the pistons just froze up almost immediately, lever got all stiff with pads dragging the rotor for the rest of the ride. Annoying. My v-brakes have behaved better in these temperatures.

    No leaking though.

  15. #15
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    Quote Originally Posted by GrantB
    I encountered non functional Hayes HFX 9 brakes during a race that started at about 19 F a couple of weeks ago. The first descent was an eye opener as the brakes simply didn't work without some serious coaxing. Every subsequent descent was the same. When the brakes did work, the lever had absolutely no throw. Kind of freaked me out.

    There were a couple of good sized water crossings on the ride. You get wet.

    These brakes run DOT3 fluid. First hydros I've ever owned. Lots of folks had similar experiences. Do you think this was a problem with the fluid, as in they need a bleed? The piston seals? Glazed up rotors? A combination of all?

    Makes me want to go back to BB7s, I'll tell you that.
    Sounds like you might have had ice on the rotor.

  16. #16
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    Quote Originally Posted by sk1er18
    im not sure how much heat is actually generated... but when I ride on extremely cold days I start out with some light brake pressure to "pre-heat" the caliper and fluid some. How much does it help? Not sure..... but it makes sense in my head and couldn't hurt to try
    of course it helps, have you not seen the BMW commercials where they're making a big deal that their brakes are so advanced they put a little pressure when wet to dry the brakes?

  17. #17
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    My wife's winter bike has Juicy 3s [DOT brake fluid], and they perform fine down to -30C. I have Shimano SLX [mineral oil], and they start to get really stiff at -20C or colder but are still functional, just with pretty much zero modulation. No leaking from either set to date.
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  18. #18
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    My Maguras never had a problem in cold weather. Maybe a touch stiff if I hadn't really used them much, like the ride TO the ride, but once on the trail and getting regular use, they were fine. Probably -10F or so.

    My Avids..........mechanical. Noooo problems with cold. *grin*

  19. #19
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    Whatever temps you car brakes work in your hydraulic bike ones will as well.....

  20. #20
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    Quote Originally Posted by 006_007
    Whatever temps you car brakes work in your hydraulic bike ones will as well.....
    Somewhat. The reservoir in your car brake system is inside a heated engine compartment, so it keeps the fluid warm even in super-cold outside temps. Bike brake systems are completely exposed. Be more accurate to apply to motorcycles, same type of setup as bike disks.

  21. #21
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  22. #22
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    This winter, I've been commuting on a bike with LX hydraulics.

    I am OK down to around -10 or -15 Celsius (5 to 15 Fahrenheit).
    When it gets colder than that, the levers get "hard" and I get some drag.

    I get this even if I am not using the brakes. During my 30 minute commute, I brake a couple of times during the first minute, after taking the bike out of semi-warm storage, and I am OK after that. Then I go without braking for about 20 minutes and the symptoms start after 10 or 15 minutes.

    I just saw a comment from a mech, saying that Shimano's plastic hoses shrink a lot in the cold. This would explain the behavior of my brakes.

  23. #23
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    Quote Originally Posted by perttime
    I just saw a comment from a mech, saying that Shimano's plastic hoses shrink a lot in the cold. This would explain the behavior of my brakes.
    Oh yeah? That might be the excuse I need to switch to steel lines...
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  24. #24
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    My Magura Marta's are a mess in cold weather. I could bleed them perfectly, go out for a ride, and at least one of them turns to mush if it is below zero outside. No idea what causes it, but I had the problem with 07, 08, and 09 sets!

  25. #25
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    actually most of the lines and all calipers in a car are exposed. it does not circulate. only the master is under the hood. so yes they can be considered the same. except for maybe the type of fluid. everything on a car is in larger proportions, the cross-sectional area of the o-rings, pistons, etc. the bigger the oring, the more allowance for expansion and contraction.

    Quote Originally Posted by heff®
    Somewhat. The reservoir in your car brake system is inside a heated engine compartment, so it keeps the fluid warm even in super-cold outside temps. Bike brake systems are completely exposed. Be more accurate to apply to motorcycles, same type of setup as bike disks.

  26. #26
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    Elixer cr's as cold as -6 f. No issues so far .

  27. #27
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    Quote Originally Posted by nanook93
    So I bundled up and hit my local mtb trail today. Probably low 20s (F) when I headed out, only in the mid-teens when I finished just after sundown. However, I slapped the knobby wheelset on my hardtail (linear-pull brakes) instead of riding the full-susp. While I was out, I started to wonder how well the Avid Juicy 5s on my full-susp would work in those temps. How low do temps have to be before hydraulic brakes can't handle it? Anybody out there have some thoughts/experiences?
    well every car , truck and snowplow uses hydro brakes

  28. #28
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    Quote Originally Posted by heff®
    Somewhat. The reservoir in your car brake system is inside a heated engine compartment, so it keeps the fluid warm even in super-cold outside temps. Bike brake systems are completely exposed. Be more accurate to apply to motorcycles, same type of setup as bike disks.
    yeah but its not a circulating system, the fluid will be warm in the master cylinder after the car warms up for awhile but the calipers will be cold and will stay cold and wet. the car brakes (pads and rotors ) will however get hotter faster than a bike rotor would
    I dont think its the fluid thats a problem on bikes .
    I think its more to do with the seals and rotors. On shimano brakes the seal on the piston is square edged and helps to retract the piston when the pressure is released. if this was to stiffen up at below a certain temp. I could see how the performance would suffer. Im sure the basic design is the same on all, just maybe different tolerances and rubber compounds to account for temp. variants. anyone have similar problems with mech. disk brakes?

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