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Can hydraulic brake levers get hot when brakes overheat?


Can I put bullhorn bars on a bike with hydraulic disc brakesHydraulic brakes feel looseShimano Hydraulic disc brakes- Lever compatibilityWill running hydraulic brake levers upside down affect performanceSRAM Drop bar to MTB hydraulic brake interoperabilityInteroperability of hydraulic disc brakes and levers between model lines/manufacturersCan hydraulic disk brakes be incrementally upgraded?Shimano Hydraulic Disc Brakes vs Tektro Hydraulic Disc BrakesMaintenance on hydraulic disc brakesShimano MTB levers with Shimano flat mount road disk brakes (hydraulic)













1















If your hydraulic brakes get hot, can this heat ever travel to your brake levers. Can your levers feel hot or is this my imagination?










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  • 1





    Your hands can get hot, from the muscles working, the friction between hand and lever, and the lack of airflow.

    – Daniel R Hicks
    10 hours ago











  • The fluid will expand a bit and your hands will feel the levers becoming stiffer which feels like they're pushing back out on their own a bit. Could that be causing a perception of heat ?

    – Criggie
    1 hour ago















1















If your hydraulic brakes get hot, can this heat ever travel to your brake levers. Can your levers feel hot or is this my imagination?










share|improve this question









New contributor




john is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.















  • 1





    Your hands can get hot, from the muscles working, the friction between hand and lever, and the lack of airflow.

    – Daniel R Hicks
    10 hours ago











  • The fluid will expand a bit and your hands will feel the levers becoming stiffer which feels like they're pushing back out on their own a bit. Could that be causing a perception of heat ?

    – Criggie
    1 hour ago













1












1








1








If your hydraulic brakes get hot, can this heat ever travel to your brake levers. Can your levers feel hot or is this my imagination?










share|improve this question









New contributor




john is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












If your hydraulic brakes get hot, can this heat ever travel to your brake levers. Can your levers feel hot or is this my imagination?







hydraulic-disc-brake






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edited 1 hour ago









Criggie

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asked 10 hours ago









johnjohn

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  • 1





    Your hands can get hot, from the muscles working, the friction between hand and lever, and the lack of airflow.

    – Daniel R Hicks
    10 hours ago











  • The fluid will expand a bit and your hands will feel the levers becoming stiffer which feels like they're pushing back out on their own a bit. Could that be causing a perception of heat ?

    – Criggie
    1 hour ago












  • 1





    Your hands can get hot, from the muscles working, the friction between hand and lever, and the lack of airflow.

    – Daniel R Hicks
    10 hours ago











  • The fluid will expand a bit and your hands will feel the levers becoming stiffer which feels like they're pushing back out on their own a bit. Could that be causing a perception of heat ?

    – Criggie
    1 hour ago







1




1





Your hands can get hot, from the muscles working, the friction between hand and lever, and the lack of airflow.

– Daniel R Hicks
10 hours ago





Your hands can get hot, from the muscles working, the friction between hand and lever, and the lack of airflow.

– Daniel R Hicks
10 hours ago













The fluid will expand a bit and your hands will feel the levers becoming stiffer which feels like they're pushing back out on their own a bit. Could that be causing a perception of heat ?

– Criggie
1 hour ago





The fluid will expand a bit and your hands will feel the levers becoming stiffer which feels like they're pushing back out on their own a bit. Could that be causing a perception of heat ?

– Criggie
1 hour ago










2 Answers
2






active

oldest

votes


















6














I've never heard of anyone having that issue before. The heat would have to travel all the way up the hose, even then still having to warm up all of the body of the brake lever before heating the part that you would pull. If you're pulling your brakes very hard for a long time, then it's more likely to be related to the strain of pulling them or cutting circulation.






share|improve this answer


















  • 4





    Since the brake fluid is constrained in a narrow tube, the transfer up it would have to be entirely by conduction: there'd be no appreciable convection. That conduction would be slowed by the cooling effect of air passing over the brake line. So I agree that it's very unlikely that brake heat will reach the levers.

    – David Richerby
    10 hours ago


















5














No, the thermal conductivity of brake hose/fluid is way too low.



I've run the numbers on this -- very roughly to make the calculations simpler. I've assumed the hose isn't cooled by airflow for some reason and a solid hose or equivalently that the fluid has the same thermal conductivity. Even the lever is assumed not to lose any heat to the air. All these assumptions maximise the amount of heat delivered to the lever.



Lets assume the hose is PTFE, which decomposes at 200°C and has a thermal conductivity of 0.5 W/m.K (the highest value I saw). I'll take a hose outside diameter of 6 mm, length 1 m. To feel warm the lever would have to get to something like 40°C, giving a temperature drop of 160°C at the point where the caliper end of the hose got so it it would be giving off toxic fumes, i.e. the absolute maximum.



Working this through, you'd be conducting 2 mW of heat to the lever. If the lever is 100 g of aluminium with a specific heat capacity of 900 J/kgK, this 2 mW it would take 12.5 hours to warm by 1°C.



Some steels have 100× the thermal conductivity of PTFE. Brake cables could conduct 200 mW for the same caliper temperature, and only take 7.5 minutes to warm by 1°C - but still an hour or two of non-stop braking to get from ambient to warm.






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    2 Answers
    2






    active

    oldest

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    2 Answers
    2






    active

    oldest

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    active

    oldest

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    active

    oldest

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    6














    I've never heard of anyone having that issue before. The heat would have to travel all the way up the hose, even then still having to warm up all of the body of the brake lever before heating the part that you would pull. If you're pulling your brakes very hard for a long time, then it's more likely to be related to the strain of pulling them or cutting circulation.






    share|improve this answer


















    • 4





      Since the brake fluid is constrained in a narrow tube, the transfer up it would have to be entirely by conduction: there'd be no appreciable convection. That conduction would be slowed by the cooling effect of air passing over the brake line. So I agree that it's very unlikely that brake heat will reach the levers.

      – David Richerby
      10 hours ago















    6














    I've never heard of anyone having that issue before. The heat would have to travel all the way up the hose, even then still having to warm up all of the body of the brake lever before heating the part that you would pull. If you're pulling your brakes very hard for a long time, then it's more likely to be related to the strain of pulling them or cutting circulation.






    share|improve this answer


















    • 4





      Since the brake fluid is constrained in a narrow tube, the transfer up it would have to be entirely by conduction: there'd be no appreciable convection. That conduction would be slowed by the cooling effect of air passing over the brake line. So I agree that it's very unlikely that brake heat will reach the levers.

      – David Richerby
      10 hours ago













    6












    6








    6







    I've never heard of anyone having that issue before. The heat would have to travel all the way up the hose, even then still having to warm up all of the body of the brake lever before heating the part that you would pull. If you're pulling your brakes very hard for a long time, then it's more likely to be related to the strain of pulling them or cutting circulation.






    share|improve this answer













    I've never heard of anyone having that issue before. The heat would have to travel all the way up the hose, even then still having to warm up all of the body of the brake lever before heating the part that you would pull. If you're pulling your brakes very hard for a long time, then it's more likely to be related to the strain of pulling them or cutting circulation.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 10 hours ago









    Carbon side upCarbon side up

    1,862316




    1,862316







    • 4





      Since the brake fluid is constrained in a narrow tube, the transfer up it would have to be entirely by conduction: there'd be no appreciable convection. That conduction would be slowed by the cooling effect of air passing over the brake line. So I agree that it's very unlikely that brake heat will reach the levers.

      – David Richerby
      10 hours ago












    • 4





      Since the brake fluid is constrained in a narrow tube, the transfer up it would have to be entirely by conduction: there'd be no appreciable convection. That conduction would be slowed by the cooling effect of air passing over the brake line. So I agree that it's very unlikely that brake heat will reach the levers.

      – David Richerby
      10 hours ago







    4




    4





    Since the brake fluid is constrained in a narrow tube, the transfer up it would have to be entirely by conduction: there'd be no appreciable convection. That conduction would be slowed by the cooling effect of air passing over the brake line. So I agree that it's very unlikely that brake heat will reach the levers.

    – David Richerby
    10 hours ago





    Since the brake fluid is constrained in a narrow tube, the transfer up it would have to be entirely by conduction: there'd be no appreciable convection. That conduction would be slowed by the cooling effect of air passing over the brake line. So I agree that it's very unlikely that brake heat will reach the levers.

    – David Richerby
    10 hours ago











    5














    No, the thermal conductivity of brake hose/fluid is way too low.



    I've run the numbers on this -- very roughly to make the calculations simpler. I've assumed the hose isn't cooled by airflow for some reason and a solid hose or equivalently that the fluid has the same thermal conductivity. Even the lever is assumed not to lose any heat to the air. All these assumptions maximise the amount of heat delivered to the lever.



    Lets assume the hose is PTFE, which decomposes at 200°C and has a thermal conductivity of 0.5 W/m.K (the highest value I saw). I'll take a hose outside diameter of 6 mm, length 1 m. To feel warm the lever would have to get to something like 40°C, giving a temperature drop of 160°C at the point where the caliper end of the hose got so it it would be giving off toxic fumes, i.e. the absolute maximum.



    Working this through, you'd be conducting 2 mW of heat to the lever. If the lever is 100 g of aluminium with a specific heat capacity of 900 J/kgK, this 2 mW it would take 12.5 hours to warm by 1°C.



    Some steels have 100× the thermal conductivity of PTFE. Brake cables could conduct 200 mW for the same caliper temperature, and only take 7.5 minutes to warm by 1°C - but still an hour or two of non-stop braking to get from ambient to warm.






    share|improve this answer



























      5














      No, the thermal conductivity of brake hose/fluid is way too low.



      I've run the numbers on this -- very roughly to make the calculations simpler. I've assumed the hose isn't cooled by airflow for some reason and a solid hose or equivalently that the fluid has the same thermal conductivity. Even the lever is assumed not to lose any heat to the air. All these assumptions maximise the amount of heat delivered to the lever.



      Lets assume the hose is PTFE, which decomposes at 200°C and has a thermal conductivity of 0.5 W/m.K (the highest value I saw). I'll take a hose outside diameter of 6 mm, length 1 m. To feel warm the lever would have to get to something like 40°C, giving a temperature drop of 160°C at the point where the caliper end of the hose got so it it would be giving off toxic fumes, i.e. the absolute maximum.



      Working this through, you'd be conducting 2 mW of heat to the lever. If the lever is 100 g of aluminium with a specific heat capacity of 900 J/kgK, this 2 mW it would take 12.5 hours to warm by 1°C.



      Some steels have 100× the thermal conductivity of PTFE. Brake cables could conduct 200 mW for the same caliper temperature, and only take 7.5 minutes to warm by 1°C - but still an hour or two of non-stop braking to get from ambient to warm.






      share|improve this answer

























        5












        5








        5







        No, the thermal conductivity of brake hose/fluid is way too low.



        I've run the numbers on this -- very roughly to make the calculations simpler. I've assumed the hose isn't cooled by airflow for some reason and a solid hose or equivalently that the fluid has the same thermal conductivity. Even the lever is assumed not to lose any heat to the air. All these assumptions maximise the amount of heat delivered to the lever.



        Lets assume the hose is PTFE, which decomposes at 200°C and has a thermal conductivity of 0.5 W/m.K (the highest value I saw). I'll take a hose outside diameter of 6 mm, length 1 m. To feel warm the lever would have to get to something like 40°C, giving a temperature drop of 160°C at the point where the caliper end of the hose got so it it would be giving off toxic fumes, i.e. the absolute maximum.



        Working this through, you'd be conducting 2 mW of heat to the lever. If the lever is 100 g of aluminium with a specific heat capacity of 900 J/kgK, this 2 mW it would take 12.5 hours to warm by 1°C.



        Some steels have 100× the thermal conductivity of PTFE. Brake cables could conduct 200 mW for the same caliper temperature, and only take 7.5 minutes to warm by 1°C - but still an hour or two of non-stop braking to get from ambient to warm.






        share|improve this answer













        No, the thermal conductivity of brake hose/fluid is way too low.



        I've run the numbers on this -- very roughly to make the calculations simpler. I've assumed the hose isn't cooled by airflow for some reason and a solid hose or equivalently that the fluid has the same thermal conductivity. Even the lever is assumed not to lose any heat to the air. All these assumptions maximise the amount of heat delivered to the lever.



        Lets assume the hose is PTFE, which decomposes at 200°C and has a thermal conductivity of 0.5 W/m.K (the highest value I saw). I'll take a hose outside diameter of 6 mm, length 1 m. To feel warm the lever would have to get to something like 40°C, giving a temperature drop of 160°C at the point where the caliper end of the hose got so it it would be giving off toxic fumes, i.e. the absolute maximum.



        Working this through, you'd be conducting 2 mW of heat to the lever. If the lever is 100 g of aluminium with a specific heat capacity of 900 J/kgK, this 2 mW it would take 12.5 hours to warm by 1°C.



        Some steels have 100× the thermal conductivity of PTFE. Brake cables could conduct 200 mW for the same caliper temperature, and only take 7.5 minutes to warm by 1°C - but still an hour or two of non-stop braking to get from ambient to warm.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 6 hours ago









        Chris HChris H

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