Master cylinder upgrade

[mlivkovich]

I read a lot about 4 pot caliper upgrades and everyone who installed them say that braking is improved. I also put 4 pot calipers that comes with TL1000S usd forks but I cannot see major difference. If I use TL master cylinder  with 14 mm piston diameter instead of gsx 5/8" piston diameter,  will it be better due to better pump/caliper piston ratio?

[gsxbarmy]

From what I have read, upgrading to a radial master cylinder is supposed to give a better percentage improvement in braking than changing the calipers. Whether that is true for the TL master cylinder I don't know, I don't know what type of master cylinder the TL one is.

[mlivkovich]

TL has axial master cylinder just like gsx has but piston diameter is smaller, so it means that less force is needed on lever using TL's cylinder. 

[KiwiCol]

smaller piston - smaller displacement of fluid,  less braking force

[mlivkovich]

Smaller piston, more braking force
Force depends on pressure, not on displacement
Bigger piston to piston diameter ratio, more braking force.

[gsxbarmy]

Looking at all the responses - I think the answer is try it, as it sounds like it should improve braking. Just be careful with initial tests!

[KiwiCol]

Ok, if you were to move 1 cc of brake fluid and 10 cc of brake fluid, which would move the pads more? 1cc or 10cc?

[mlivkovich]

It doesn't matter how much fluid do you move, it matters how much pressure is created. Lets say brake pads need some amount of pressure to brake efficiently and both gsx and TL pump will create it. But you will need smaller force and more travel on lever that pushes smaller piston. It means gsx lever has to be pulled harder with less travel to create same pressure and force on brake pads.
Logic, isn't it? 

[grog]

When the size of the master cylinder piston increases, the output pressure of the master cylinder decreases. A smaller master cylinder piston will exert more line pressure with the same amount of force (pedal ratio) than a master cylinder piston with a larger piston area.

[Hooli]

But equally a smaller master cylinder piston increases lever movement as it has to move further to push enough fluid down to move the caliper pistons enough to apply the pressure to the pads.

It's all leverage, doesn't matter if it's hydraulic, cable or rod brakes.

[grog]

exactly correct Hooli.

[mlivkovich]

But equally a smaller master cylinder piston increases lever movement as it has to move further to push enough fluid down to move the caliper pistons enough to apply the pressure to the pads.

It's all leverage, doesn't matter if it's hydraulic, cable or rod brakes.

Conclusion is that 4 piston calipers are not real benefit until proper master cylinder is used?

[grog]

any idea of piston area, 4 pots compared to 6 pots?

[Hooli]

But equally a smaller master cylinder piston increases lever movement as it has to move further to push enough fluid down to move the caliper pistons enough to apply the pressure to the pads.

It's all leverage, doesn't matter if it's hydraulic, cable or rod brakes.

Conclusion is that 4 piston calipers are not real benefit until proper master cylinder is used?

Depends on the area of the pistons.

Of course as they'll take smaller pads there is more chance of overheating them if used in a spirited manner with the same pad material.

[mlivkovich]

Gsx
- master cyclinder diameter - 5/8" (15.875mm), area - 2 cm2
- caliper piston diameter - 27mm x 12 pcs, area - 68.67 cm2
- ratio 1/34.33

TL
- master cylinder diameter - 14 mm
- caliper piston diameter - 27mm x 4 pcs, area - 22.89 cm2
                                            - 30mm x 4 pcs, area - 28.26 cm2
- ratio 1/33.24
My setup (gsx pump, TL calipers) ratio 1/25.57

If my calculations were correct, I found reason why is front brake lever harder after 4 pots conversion.