There are many threads on here about doing brake up grades. All of these threads are on how to do the upgrades.
In this thread I'd like to talk about the why the upgrades work.
Basically a brake uses the pressure you exert on the brake lever through mechanical or hydralic means to push a solid object against a rotating object to stop the rotaion.
Most of the people on here that do upgrades, do them on the fropnt brake. They start with the 77 up single piston caliper. I'll use this system as the starting point.
When you pull on the brake lever, lets say you use 10 lbs of force. This force is altered by the brake lever ratio. I measured my brake lever from the pivot point to the place where it pushes on the piston. I also measured from the pivot point to where my finger closet to the pivot sets and to where my finger fartest from the pivot sets.
Pivot to piston is about 1 inch. Pivot to first finger about 4 inches, to last finger about 6.5 inches. An average of about 5.25 inches. That gives a ratio of about 5.25-1. The 10 lbs of force on the lever is increased by 5.25 times or about 52.5 lbs on the piston.
This force is converted from lbs to psi by the piston. To calulate this you need to find the area on the piston in inches. The stock 14 mm piston is .551 inches. To find the area the formula is pi x R squared. R is 1/2 of the diameter, so .551 devided by 2 is .2755. Square this by multiplying by itself. .2755 x .2755 = .0759, this X pi or 3.14 = .238 square inches. To get psi, you need devide 1 inch by the area of the piston. 1 devided by .238 = 4.2. Now multiply the 52.5 lbs by the 4.2 you get 220.5 psi.
This 220.5 psi is evenly spread throughout the system.
Now down at the caliper the piston converts this pressure to force that pushes the pads against the rotor.
First you need to find the area of the piston. The piston is 38 mm or 1.49 inches. devide by 2 is .745. .745 x.745 = .555 x 3.14 =1.742 Devide the psi by the square inches, 220.5 devived by 1.742 = 126.5 lbs of force pushing the pads against the rotor.
Now that we have the force reguired to make the bike stop with the stock set up lets look at two of the easiest mods. Adding a second caliper and rotor. Or using a smaller M/C with the stock single caliper/rotor.
Now when 10 lbs of force is applied to the lever the pressure of 220.5 is created in the system. This pressure is the same through out the system. So the second caliper does the same as the first, creates 126.5 lbs of force to push the pads to the rotor. This doubles the force applied so doubles the brake power. Now to stop the bike only 5 lbs of force on the lever stops the bike.
Using a smaller M/C such as the 11 mm reccomended gives us a .433 bore, 1/2 of .433 is .216. .216 x .216 = .046 X 3.14 = .146 si.
10 lbs at the lever = 52.5 at the M/C.
1 devided by .146 = 6.84. 52.5 x 6.84 = 359.1 psi. You see the increase in pressure from 220.5 to 359.1 now at the caliper it still has the 1.742 area so divide the psi by the area you get 206 lbs of force pushing the pads to the rotor.
As you can see the force increased almost the same as with the dual caliper set up. On the lever you will get a difference of about 2.6 lbs between the two. I doubt most will feel a difference between the two.
I know these figures are rough. I'm just guessing on the force applied to the lever, but all the other things apply.
You can use the same principles to determine how much effect any M/C or caliper will have on braking. Front or rear brakes. On drum brakes there may not be as much varibles to experiment with but the same basic principle applies, increase the pressure of the shoes to the drum and the brake will be better.
These changes will effect the travel of the lever. It increase the travel but the less force required to work the brake will be less, so they kinda balance out.
The reduction in the effort at the lever greatly increases the feel of the brake. With the stock stytem the feel can be somewhat wooden. This means as you icrease the pressure on the lever it feels pretty much the same even as the brake locks. With the decreased pressure you can feel the changes as you pull the lever harder. With just a few practice runs you can by feel tell when the brake is about to lock and you can release just enough pressure to prevent lock up.
I guess it would be possible to go to too small a M/C and run out of lever travel before the brakes worked, but that would have to be a very extremly small M/C.
Leo
In this thread I'd like to talk about the why the upgrades work.
Basically a brake uses the pressure you exert on the brake lever through mechanical or hydralic means to push a solid object against a rotating object to stop the rotaion.
Most of the people on here that do upgrades, do them on the fropnt brake. They start with the 77 up single piston caliper. I'll use this system as the starting point.
When you pull on the brake lever, lets say you use 10 lbs of force. This force is altered by the brake lever ratio. I measured my brake lever from the pivot point to the place where it pushes on the piston. I also measured from the pivot point to where my finger closet to the pivot sets and to where my finger fartest from the pivot sets.
Pivot to piston is about 1 inch. Pivot to first finger about 4 inches, to last finger about 6.5 inches. An average of about 5.25 inches. That gives a ratio of about 5.25-1. The 10 lbs of force on the lever is increased by 5.25 times or about 52.5 lbs on the piston.
This force is converted from lbs to psi by the piston. To calulate this you need to find the area on the piston in inches. The stock 14 mm piston is .551 inches. To find the area the formula is pi x R squared. R is 1/2 of the diameter, so .551 devided by 2 is .2755. Square this by multiplying by itself. .2755 x .2755 = .0759, this X pi or 3.14 = .238 square inches. To get psi, you need devide 1 inch by the area of the piston. 1 devided by .238 = 4.2. Now multiply the 52.5 lbs by the 4.2 you get 220.5 psi.
This 220.5 psi is evenly spread throughout the system.
Now down at the caliper the piston converts this pressure to force that pushes the pads against the rotor.
First you need to find the area of the piston. The piston is 38 mm or 1.49 inches. devide by 2 is .745. .745 x.745 = .555 x 3.14 =1.742 Devide the psi by the square inches, 220.5 devived by 1.742 = 126.5 lbs of force pushing the pads against the rotor.
Now that we have the force reguired to make the bike stop with the stock set up lets look at two of the easiest mods. Adding a second caliper and rotor. Or using a smaller M/C with the stock single caliper/rotor.
Now when 10 lbs of force is applied to the lever the pressure of 220.5 is created in the system. This pressure is the same through out the system. So the second caliper does the same as the first, creates 126.5 lbs of force to push the pads to the rotor. This doubles the force applied so doubles the brake power. Now to stop the bike only 5 lbs of force on the lever stops the bike.
Using a smaller M/C such as the 11 mm reccomended gives us a .433 bore, 1/2 of .433 is .216. .216 x .216 = .046 X 3.14 = .146 si.
10 lbs at the lever = 52.5 at the M/C.
1 devided by .146 = 6.84. 52.5 x 6.84 = 359.1 psi. You see the increase in pressure from 220.5 to 359.1 now at the caliper it still has the 1.742 area so divide the psi by the area you get 206 lbs of force pushing the pads to the rotor.
As you can see the force increased almost the same as with the dual caliper set up. On the lever you will get a difference of about 2.6 lbs between the two. I doubt most will feel a difference between the two.
I know these figures are rough. I'm just guessing on the force applied to the lever, but all the other things apply.
You can use the same principles to determine how much effect any M/C or caliper will have on braking. Front or rear brakes. On drum brakes there may not be as much varibles to experiment with but the same basic principle applies, increase the pressure of the shoes to the drum and the brake will be better.
These changes will effect the travel of the lever. It increase the travel but the less force required to work the brake will be less, so they kinda balance out.
The reduction in the effort at the lever greatly increases the feel of the brake. With the stock stytem the feel can be somewhat wooden. This means as you icrease the pressure on the lever it feels pretty much the same even as the brake locks. With the decreased pressure you can feel the changes as you pull the lever harder. With just a few practice runs you can by feel tell when the brake is about to lock and you can release just enough pressure to prevent lock up.
I guess it would be possible to go to too small a M/C and run out of lever travel before the brakes worked, but that would have to be a very extremly small M/C.
Leo
