Can hydraulic brake levers get hot when brakes overheat?












3















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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  • 4





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

    – Daniel R Hicks
    yesterday






  • 2





    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
    yesterday
















3















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.
















  • 4





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

    – Daniel R Hicks
    yesterday






  • 2





    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
    yesterday














3












3








3








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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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.











share|improve this question









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









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edited yesterday









Criggie

44.7k573151




44.7k573151






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asked yesterday









johnjohn

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161




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






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Check out our Code of Conduct.








  • 4





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

    – Daniel R Hicks
    yesterday






  • 2





    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
    yesterday














  • 4





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

    – Daniel R Hicks
    yesterday






  • 2





    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
    yesterday








4




4





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

– Daniel R Hicks
yesterday





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

– Daniel R Hicks
yesterday




2




2





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
yesterday





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
yesterday










2 Answers
2






active

oldest

votes


















10














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 above about 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


























  • Wait, PTFE decomposes at 200°C? I've been using my 3D printer with PTFE in-nozzle lining heated up to 235°C or so, and many people do this with no ill effects. I haven't noticed any physical problems with the tubing when I pull it out. Should I be worried?

    – Dmitry Kudriavtsev
    yesterday











  • @Dmitry if you bought the nozzle like that, and you're using it as specified, don't worry. I've seen various figures and this is the lowest, but was on the page I got the thermal conductivity from. Non stick cookware is also used to similar temperatures. I've toned down the wording of that bit

    – Chris H
    22 hours ago













  • @Chris H I always loved "word problems" in the math and physics classes i took during my school days. Felt it gave a little substance to the lean purity of an equation or a set of given numbers to crunch, That they often seemed to slow-up those fellow students truly gifted in math only fed my favor of them. Anyway, i liked how you approached this question. Giving you an SE version of an A: upvote.

    – Jeff
    22 hours ago











  • @Jeff, thank you. Doubly so as I gave a lecture on the topic this week and used an example problem (heating a room, rather than bike-related) and I'm glad to hear it suits some people

    – Chris H
    21 hours ago



















8














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



















  • 6





    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
    yesterday











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2 Answers
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2 Answers
2






active

oldest

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active

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active

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10














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 above about 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


























  • Wait, PTFE decomposes at 200°C? I've been using my 3D printer with PTFE in-nozzle lining heated up to 235°C or so, and many people do this with no ill effects. I haven't noticed any physical problems with the tubing when I pull it out. Should I be worried?

    – Dmitry Kudriavtsev
    yesterday











  • @Dmitry if you bought the nozzle like that, and you're using it as specified, don't worry. I've seen various figures and this is the lowest, but was on the page I got the thermal conductivity from. Non stick cookware is also used to similar temperatures. I've toned down the wording of that bit

    – Chris H
    22 hours ago













  • @Chris H I always loved "word problems" in the math and physics classes i took during my school days. Felt it gave a little substance to the lean purity of an equation or a set of given numbers to crunch, That they often seemed to slow-up those fellow students truly gifted in math only fed my favor of them. Anyway, i liked how you approached this question. Giving you an SE version of an A: upvote.

    – Jeff
    22 hours ago











  • @Jeff, thank you. Doubly so as I gave a lecture on the topic this week and used an example problem (heating a room, rather than bike-related) and I'm glad to hear it suits some people

    – Chris H
    21 hours ago
















10














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 above about 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


























  • Wait, PTFE decomposes at 200°C? I've been using my 3D printer with PTFE in-nozzle lining heated up to 235°C or so, and many people do this with no ill effects. I haven't noticed any physical problems with the tubing when I pull it out. Should I be worried?

    – Dmitry Kudriavtsev
    yesterday











  • @Dmitry if you bought the nozzle like that, and you're using it as specified, don't worry. I've seen various figures and this is the lowest, but was on the page I got the thermal conductivity from. Non stick cookware is also used to similar temperatures. I've toned down the wording of that bit

    – Chris H
    22 hours ago













  • @Chris H I always loved "word problems" in the math and physics classes i took during my school days. Felt it gave a little substance to the lean purity of an equation or a set of given numbers to crunch, That they often seemed to slow-up those fellow students truly gifted in math only fed my favor of them. Anyway, i liked how you approached this question. Giving you an SE version of an A: upvote.

    – Jeff
    22 hours ago











  • @Jeff, thank you. Doubly so as I gave a lecture on the topic this week and used an example problem (heating a room, rather than bike-related) and I'm glad to hear it suits some people

    – Chris H
    21 hours ago














10












10








10







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 above about 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 above about 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








edited 22 hours ago

























answered yesterday









Chris HChris H

23.9k138106




23.9k138106













  • Wait, PTFE decomposes at 200°C? I've been using my 3D printer with PTFE in-nozzle lining heated up to 235°C or so, and many people do this with no ill effects. I haven't noticed any physical problems with the tubing when I pull it out. Should I be worried?

    – Dmitry Kudriavtsev
    yesterday











  • @Dmitry if you bought the nozzle like that, and you're using it as specified, don't worry. I've seen various figures and this is the lowest, but was on the page I got the thermal conductivity from. Non stick cookware is also used to similar temperatures. I've toned down the wording of that bit

    – Chris H
    22 hours ago













  • @Chris H I always loved "word problems" in the math and physics classes i took during my school days. Felt it gave a little substance to the lean purity of an equation or a set of given numbers to crunch, That they often seemed to slow-up those fellow students truly gifted in math only fed my favor of them. Anyway, i liked how you approached this question. Giving you an SE version of an A: upvote.

    – Jeff
    22 hours ago











  • @Jeff, thank you. Doubly so as I gave a lecture on the topic this week and used an example problem (heating a room, rather than bike-related) and I'm glad to hear it suits some people

    – Chris H
    21 hours ago



















  • Wait, PTFE decomposes at 200°C? I've been using my 3D printer with PTFE in-nozzle lining heated up to 235°C or so, and many people do this with no ill effects. I haven't noticed any physical problems with the tubing when I pull it out. Should I be worried?

    – Dmitry Kudriavtsev
    yesterday











  • @Dmitry if you bought the nozzle like that, and you're using it as specified, don't worry. I've seen various figures and this is the lowest, but was on the page I got the thermal conductivity from. Non stick cookware is also used to similar temperatures. I've toned down the wording of that bit

    – Chris H
    22 hours ago













  • @Chris H I always loved "word problems" in the math and physics classes i took during my school days. Felt it gave a little substance to the lean purity of an equation or a set of given numbers to crunch, That they often seemed to slow-up those fellow students truly gifted in math only fed my favor of them. Anyway, i liked how you approached this question. Giving you an SE version of an A: upvote.

    – Jeff
    22 hours ago











  • @Jeff, thank you. Doubly so as I gave a lecture on the topic this week and used an example problem (heating a room, rather than bike-related) and I'm glad to hear it suits some people

    – Chris H
    21 hours ago

















Wait, PTFE decomposes at 200°C? I've been using my 3D printer with PTFE in-nozzle lining heated up to 235°C or so, and many people do this with no ill effects. I haven't noticed any physical problems with the tubing when I pull it out. Should I be worried?

– Dmitry Kudriavtsev
yesterday





Wait, PTFE decomposes at 200°C? I've been using my 3D printer with PTFE in-nozzle lining heated up to 235°C or so, and many people do this with no ill effects. I haven't noticed any physical problems with the tubing when I pull it out. Should I be worried?

– Dmitry Kudriavtsev
yesterday













@Dmitry if you bought the nozzle like that, and you're using it as specified, don't worry. I've seen various figures and this is the lowest, but was on the page I got the thermal conductivity from. Non stick cookware is also used to similar temperatures. I've toned down the wording of that bit

– Chris H
22 hours ago







@Dmitry if you bought the nozzle like that, and you're using it as specified, don't worry. I've seen various figures and this is the lowest, but was on the page I got the thermal conductivity from. Non stick cookware is also used to similar temperatures. I've toned down the wording of that bit

– Chris H
22 hours ago















@Chris H I always loved "word problems" in the math and physics classes i took during my school days. Felt it gave a little substance to the lean purity of an equation or a set of given numbers to crunch, That they often seemed to slow-up those fellow students truly gifted in math only fed my favor of them. Anyway, i liked how you approached this question. Giving you an SE version of an A: upvote.

– Jeff
22 hours ago





@Chris H I always loved "word problems" in the math and physics classes i took during my school days. Felt it gave a little substance to the lean purity of an equation or a set of given numbers to crunch, That they often seemed to slow-up those fellow students truly gifted in math only fed my favor of them. Anyway, i liked how you approached this question. Giving you an SE version of an A: upvote.

– Jeff
22 hours ago













@Jeff, thank you. Doubly so as I gave a lecture on the topic this week and used an example problem (heating a room, rather than bike-related) and I'm glad to hear it suits some people

– Chris H
21 hours ago





@Jeff, thank you. Doubly so as I gave a lecture on the topic this week and used an example problem (heating a room, rather than bike-related) and I'm glad to hear it suits some people

– Chris H
21 hours ago











8














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



















  • 6





    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
    yesterday
















8














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



















  • 6





    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
    yesterday














8












8








8







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 yesterday









Carbon side upCarbon side up

1,882316




1,882316








  • 6





    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
    yesterday














  • 6





    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
    yesterday








6




6





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
yesterday





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
yesterday










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