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Didn't know whether to post this in Bike Tech or Noob Q&A, but here it is:
http://www.carbibles.com/brake_bible.html
http://www.carbibles.com/brake_bible.html
Brakes explained
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11,210 Posts
Actually there's some errors in that page. And in a couple of cases far more emphasis on a point than it deserves while ignoring other factors.
First off the heat is a BYPRODUCT of the slowing down and not the desired end in itself. Granted it is an unavoidable byproduct and the final balance of the physics is correct as they suggest (kinetic to thermal energy conversion) but nonetheless it's not the primary goal of the braking system to generate heat. The primary goal is to provide CONSISTENT friction in a reliable manner.
It also doesn't get into the coefficient of friction for the various materials and how these values change with varying temperatures. They only discuss the vapourizing of the bonding resins as being responsible for brake fade. But there's far more to it. The friction particles are what provides the friction and it's how they behave as the temperatures change that has far more bearing on how the pads behave than the bonding resins.
Besides, if the resins vapourized like they suggest then what the hell would hold the pads together after a while? Nope, the bonding resins are far more tolerant than they suggest. Although you CAN blame this outgassing on how some pads behave until they are "broken in". This effect is largely why some pads need to be fully heated to or beyond their normal operating temperature before they provide their best performance, ie; racing pads.
The description of the leading shoe drum design has some errors as well. In a single leading shoe design there is still two shoes but one is a leading shoe, where the pressure in put on the leading end of the shoe. The other show is a trailing shoe because the drum is rolling onto the fixed end and off the expanding end. They are right in that a leading shoe tends to be somewhat self energizing in that the rotation of the drum tends to want to push the shoe into harder contact. THis is why the twin or multi leading shoe designs were developed. However it also says that the single leading shoe design doesn't grab when you roll it backwards because of the leading shoe suddenly becoming a trailing shoe. But what about the trailing shoe that's now a leading shoe? Nope, their explanation doesn't fly. However they are right in that single action drums don't work well in reverse but it's for a different reason. Because the forces in a drum brake are largely and commonly in one direction the shoes take on a shape through wearing that works in that one direction as the shoes mate to the shapes and forces at work. This fit is CRITICAL to effective production of friction. When you roll the bike or car with these single leading shoe drums backwards and put on the brakes the shoes shift around just enough that they no longer mate up to the drum in quite the same way and you have far poorer friction for the amount of braking pressure. And THAT is why the single element drums are not as good.
THis is not to say that it's not a good article but the writer has too much emphasis on some parts while downplaying some others.
First off the heat is a BYPRODUCT of the slowing down and not the desired end in itself. Granted it is an unavoidable byproduct and the final balance of the physics is correct as they suggest (kinetic to thermal energy conversion) but nonetheless it's not the primary goal of the braking system to generate heat. The primary goal is to provide CONSISTENT friction in a reliable manner.
It also doesn't get into the coefficient of friction for the various materials and how these values change with varying temperatures. They only discuss the vapourizing of the bonding resins as being responsible for brake fade. But there's far more to it. The friction particles are what provides the friction and it's how they behave as the temperatures change that has far more bearing on how the pads behave than the bonding resins.
Besides, if the resins vapourized like they suggest then what the hell would hold the pads together after a while? Nope, the bonding resins are far more tolerant than they suggest. Although you CAN blame this outgassing on how some pads behave until they are "broken in". This effect is largely why some pads need to be fully heated to or beyond their normal operating temperature before they provide their best performance, ie; racing pads.
The description of the leading shoe drum design has some errors as well. In a single leading shoe design there is still two shoes but one is a leading shoe, where the pressure in put on the leading end of the shoe. The other show is a trailing shoe because the drum is rolling onto the fixed end and off the expanding end. They are right in that a leading shoe tends to be somewhat self energizing in that the rotation of the drum tends to want to push the shoe into harder contact. THis is why the twin or multi leading shoe designs were developed. However it also says that the single leading shoe design doesn't grab when you roll it backwards because of the leading shoe suddenly becoming a trailing shoe. But what about the trailing shoe that's now a leading shoe? Nope, their explanation doesn't fly. However they are right in that single action drums don't work well in reverse but it's for a different reason. Because the forces in a drum brake are largely and commonly in one direction the shoes take on a shape through wearing that works in that one direction as the shoes mate to the shapes and forces at work. This fit is CRITICAL to effective production of friction. When you roll the bike or car with these single leading shoe drums backwards and put on the brakes the shoes shift around just enough that they no longer mate up to the drum in quite the same way and you have far poorer friction for the amount of braking pressure. And THAT is why the single element drums are not as good.
THis is not to say that it's not a good article but the writer has too much emphasis on some parts while downplaying some others.
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202 Posts
k good, i thought there was some stuff wrong, this is why i never fully trust anything from the net.
for god sakes, its not heat that slows anything down, like when you bail and slide on asphalt, its not the fact that your ass is now 80 degrees thats slows you down, but yes, it is the conversion of energy types as "energy can neither be created or destroyed", so its gotta go somewhere.....heat, and occasionally sound.
for god sakes, its not heat that slows anything down, like when you bail and slide on asphalt, its not the fact that your ass is now 80 degrees thats slows you down, but yes, it is the conversion of energy types as "energy can neither be created or destroyed", so its gotta go somewhere.....heat, and occasionally sound.
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