brake upgrade ....What's the science?

[pbassred]

I understand that brakes are friction devices. In order to generate more friction, you need more friction area, so thats why you fit larger disks and pads. I also understand that unless you have extra force to spread across those bigger pads you won't gain, so that's why you fit bigger calipers with bigger ( or two) pistons.

What i DON'T get is where those bigger caliper pistons get their force from. After all, a hydraulic piston generates its mechanical force as a combination of fluid flow and pressure. If you increase the CSA of the piston you require an increase in fluid flow to drive it. If you don't have that flow available, the pressure will drop (less over all pressure at the pads). Unless you change your brake servo, the only way to get more fluid driving that bigger piston is if your foot travels further on the peddle.

what am I missing here?

[Lofty86]

Its the levering force that counts as much as anything mate.

The further the caliper from the hub, the greater the force applyed.

HTH.
Dave

[vwcabriolet1971]

The combined CSA of the two pot caliper will be greater than the single pot version . Also the greater disc clamping force will be more evenly spread across the larger pads. The actual flow / displacement capacity requirement is quite small as the pads are quite close to the discs .
However 2 pot (or 4 pot) calipers should have larger displacement master cylinders when compared with the original single pot . As the safety factor of OEM master cylinders is quite high a lot of upgrading owners get away with it .

[Lofty86]

Also, although the area behind the piston(s) is greater, the brake system is bled, and this is filled.
Yeah I know you still need more fluid to push it the same distance, but you will have no worry on brakes you would be fitting.

And if you are worried, then like was said above, replace the master (maby from an S4 / RS4, dont know if there bigger) and it will be fine.
Dave