master cylinder advice

[yorkie_chris]

Soory if that sounded aggressive or anything.... I should be breathalysed before I can sign into the forum lol.

So many people have this wierd impression that a larger m/c will be more powerful "because it moves more fluid innit" ... No! Fail! An m/c of smaller bore will give the most absolute braking power. Just google hydraulic force multiplier.

In the m/c. Pressure = force1 / area1
In the caliper force2 = Pressure x area2 (this is for force on the pads, so actual BRAKING EFFORT)

So. Force on pads = force on mastercylinder x (area1/area2)

So to get more force on the pads, make the area of piston in the caliper bigger (more pistons, bigger pistons), or make the area of the mastercylinder piston smaller. Or squeeze the lever harder.

The other thing to mess up that nice neat rearrangement is the leverage ratio of the lever on the mastercylinder piston. It varies from model to model.

[DarrenSV650S]

Originally Posted by yorkie_chris

Soory if that sounded aggressive or anything.... I should be breathalysed before I can sign into the forum lol.

So many people have this wierd impression that a larger m/c will be more powerful "because it moves more fluid innit" ... No! Fail! An m/c of smaller bore will give the most absolute braking power. Just google hydraulic force multiplier.

In the m/c. Pressure = force1 / area1
In the caliper force2 = Pressure x area2 (this is for force on the pads, so actual BRAKING EFFORT)

So. Force on pads = force on mastercylinder x (area1/area2)

So to get more force on the pads, make the area of piston in the caliper bigger (more pistons, bigger pistons), or make the area of the mastercylinder piston smaller. Or squeeze the lever harder.

The other thing to mess up that nice neat rearrangement is the leverage ratio of the lever on the mastercylinder piston. It varies from model to model.

Ok so your saying a larger m/c won't make your brakes more powerful. But surely (don't call me Shirley) a larger m/c will give you full braking with less lever movement no? Whereas a smaller m/c will require more lever movement to get to the same braking point

[yorkie_chris]

You are correct. But the larger one will have less pressure.

Once the discs touch the pads that is it, there is no more movement worth thinking about, any movement then is compression of fluid, flex in lever, flex in caliper, expansion of lines and compression of the disc.

Braking power is determined by the clamping force, not a function of movement.


So, a larger m/c will make them bite with less lever travel, but with less actual braking power than a smaller bore.

[DarrenSV650S]

I don't understand how it would have less pressure

[yorkie_chris]

Pressure = force / area

[DarrenSV650S]

But the area of the inside of the lines and callipers are the same. It's only the m/c piston area that's bigger and that is controlled by how much I pull the lever. So surely (don't call me Shirley) if I pull it hard enough I will get the same, if not more pressure

[yorkie_chris]

No, the m/c piston area is constant, given by ((piston diameterx10^-3)xPi) / 4

Why "if not more pressure"?

For the same force on the piston, you will develop more pressure in the system with a smaller piston.

thanks for the replys and maths lesson....

@ Northwind, what year R6/R1, sounds like the mod I've in mind .. cheers

[northwind]

I think every one with the 4-pot radial calipers gets the same m/c. Mine is off an... 05 R6, probably.

Originally Posted by northwind

I think every one with the 4-pot radial calipers gets the same m/c. Mine is off an... 05 R6, probably.

thanks man...... I'll let you guys know how it goes