V-brakes. Forces exerted on brake pads. Front vs rear pads (downhill) 70% / 30% ???
08-20-15, 08:47 AM
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V-brakes. Forces exerted on brake pads. Front vs rear pads (downhill) 70% / 30% ???
My front pads seem to be under much more stress than my rear brakes when going downhill. I try to add my own "mixing"
instead of continuous applying force to the brakes and even swerve a bit simply to loose some speed. This seems to work good.
Still, the front ones make a sound that really does not sound very nice (probably normal) No they are not worn out. So anyone who cares to enlighten me about the physics involved here or at least attempt an explanation?!
Bjoern in Norway
instead of continuous applying force to the brakes and even swerve a bit simply to loose some speed. This seems to work good.
Still, the front ones make a sound that really does not sound very nice (probably normal) No they are not worn out. So anyone who cares to enlighten me about the physics involved here or at least attempt an explanation?!
Bjoern in Norway
08-20-15, 08:55 AM
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100% once the rear wheel is off the ground.
08-20-15, 09:04 AM
#3
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Under normal or gradual braking conditions you can modulate them however you want. 100% front, 100% rear, or anywhere in between. In an emergency stop on dry pavement the front brake provides 100% of the stopping power. This is because the rear wheel is unweighted and a wheel that has no weight can't provide any stopping power. You can lock the rear wheel if you want and it won't slow you down one bit. If the rear wheel is not unweighted during an emergency stop you're simply not grabbing the front brake hard enough.
Good braking technique on long downhills involves switching between the front and rear brake so that neither one heats up too much. It's also better to grab and release the brakes in short pulses rather than drag them for a long time which creates excessive heat.
Good braking technique on long downhills involves switching between the front and rear brake so that neither one heats up too much. It's also better to grab and release the brakes in short pulses rather than drag them for a long time which creates excessive heat.
08-20-15, 09:41 AM
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^^ this should do^^ Chat up a professor of Physics at your nearest University to get a better more precise answer.
they may have a reading list of books to educate yourself on the analysis ~ thoughts from ages past.
they may have a reading list of books to educate yourself on the analysis ~ thoughts from ages past.
Last edited by fietsbob; 08-20-15 at 09:44 AM.
08-20-15, 09:51 AM
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From a technique standpoint, braking in short, threshold bursts is absolutely better (maximizes average speed), but that doesn't have anything to do with heat buildup.
08-20-15, 09:56 AM
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I've seen this claim before, but the laws of physics (conservation of energy) seem to disagree. A big force over a short time vs. a smaller force over a longer time makes no difference. Both are going to convert the same amount of kinetic energy to heat as long as they generate the same change in velocity (0.5 * mass * (v1^2 - v2^2)).
From a technique standpoint, braking in short, threshold bursts is absolutely better (maximizes average speed), but that doesn't have anything to do with heat buildup.
From a technique standpoint, braking in short, threshold bursts is absolutely better (maximizes average speed), but that doesn't have anything to do with heat buildup.
Hard braking builds up a lot of heat quickly. Doing so in short "bursts" give more cooling time for the rim/rotor.
Since heat transfer depends on the temperature differential, the hotter surface will transfer heat more quickly to the ambient air.
08-20-15, 10:02 AM
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Transfer body weight rearward when braking hard. Meaning, straighten arms and slide butt rearward on saddle. Helps with weight distribution. Doesn't matter during routine braking, in hard stops, especially downhill and mountain biking can make the difference between going over the handlebars and not.
08-20-15, 11:07 AM
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But it can have a lot to do with heat dissipation.
Hard braking builds up a lot of heat quickly. Doing so in short "bursts" give more cooling time for the rim/rotor.
Since heat transfer depends on the temperature differential, the hotter surface will transfer heat more quickly to the ambient air.
Hard braking builds up a lot of heat quickly. Doing so in short "bursts" give more cooling time for the rim/rotor.
Since heat transfer depends on the temperature differential, the hotter surface will transfer heat more quickly to the ambient air.
08-20-15, 03:44 PM
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GCN (Global Cycling Network, dozens of youtube videos) has a vid showing the results of both versus front only versus rear brakes only in stopping from
25mph (found it: https://www.youtube.com/watch?v=frIK...ion_2466383795 )
Interestingly, both brakes or fr brake only give nearly the same stopping distance.
25mph (found it: https://www.youtube.com/watch?v=frIK...ion_2466383795 )
Interestingly, both brakes or fr brake only give nearly the same stopping distance.
08-20-15, 03:56 PM
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My front pads seem to be under much more stress than my rear brakes when going downhill. I try to add my own "mixing"
instead of continuous applying force to the brakes and even swerve a bit simply to loose some speed. This seems to work good.
Still, the front ones make a sound that really does not sound very nice (probably normal) No they are not worn out. So anyone who cares to enlighten me about the physics involved here or at least attempt an explanation?!
Bjoern in Norway
instead of continuous applying force to the brakes and even swerve a bit simply to loose some speed. This seems to work good.
Still, the front ones make a sound that really does not sound very nice (probably normal) No they are not worn out. So anyone who cares to enlighten me about the physics involved here or at least attempt an explanation?!
Bjoern in Norway
There is a good chance you have a bunch of aluminium from your front rim embedded in your brake pads, there because your pads are too hard for the rims! This will make a horrible scraping sound. The temporary fix is to pick out the bits with a pocket knife and sand the face of the pads with sandpaper to get the nasty glaze off them. That'll give you time to buy some good pads made by a company like Kool Stop, SwissStop or whoever. You could keep doing the temporary fix, but those bits of rim are bits of your rim wearing out faster than they need too. As a bonus, your braking will feel much better, metal on metal never feels good! Good pads should wear out reasonably fast, so it's them wearing and not your rim.
08-21-15, 02:41 PM
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NB: some road brake pads are made with "embedded bits of aluminum" in the pad as a wear indicator, once you see the bits you change
the pad. When I first saw such I too thought from rim but close exam of the rim showed no wear spots where bits could have come from.
Subsequent experience shows this to be the manufacturers way of telling you to change the pads.
the pad. When I first saw such I too thought from rim but close exam of the rim showed no wear spots where bits could have come from.
Subsequent experience shows this to be the manufacturers way of telling you to change the pads.
