What makes brakes "good"

[forester sti]

I'm sure there is a science behind this!

But, surely the number of pistons in a caliper isn't all important??
eg. the same amount of fluid is pumped in the apply pressure to the disc!!
So whether that is pushing 4 big pistons (newage brembos) or 8 small ones (Ksports finest) then it's doing the same job???
Pads have a rigid metal plate on their backing so speading the load may not be that important!

OR Is it the physical size of the pads??
eg. Newage brembo pads are a similar size to AP Racing 6pots pads!!
or you can get those huge Tar-ox 12 pots that have 4 pads per disc hence spreading the pressure over a much larger area, but that would mean that the "point pressure" wouldn't be as much as on a smaller pad!!

When I needed bigger brakes, I went for the biggest disc I could fit under 18" wheels, So 355mm discs and I went for the Porcshe GT3 6 pots which have very large pads, about 1 and a half times bigger than the brembos that were on it! same with the Boxster S rear calipers!
AP Racing would probably have been better, but the porsche ones are very pretty!

Assuming that you are already using the best pad material, the best fluid and braided lines!
I'd be interested in your opinions!

Dan

[J_MC_G]

Easier to push (for the fluid) 6 smaller lighter pistons than 4 bigger heavier ones through the build up of road grim on the seal and dust seal?

[brendy]

its a combination of the whole package, even tyres play their part in a good brake setup.

[Scubbay]

Imo it relys on the area that the pistons are applying on the pad, more pistons but pushing on the same area shouldnt really give a better performance tbh. Brakes rely on friction, friction relies on contact area. It also relies on the pressure applied as well though. Force = Pressure*Area so if the same force is applied through the fluid to a smaller area it should apply more pressure and brake better I guess. So its a throw up I guess, bigger pistons have a bigger contact area and smaller pistons will apply more pressure, ideally you want as many pistons of as big a size as possible. Really to get better brakes you need to upgrade to as big a caliper as you can, they should have the most amount of "large" pistons therefore getting the best of both worlds.

Tbh I think the brembos are more than up to the job with good pads/discs/fluid. The discs and pads are going to make the biggest difference to the braking ability of the car rather than the calipers. Its just that most uprated calipers come with uprated discs and pads.

Stefan

[forester sti]

Great reply,
But,
The bigger the caliper, being "powered" by the same amount of fluid, as a smaller caliper, would then spread the force over a larger contact area,
So at a lesser pressure! due to there being a greater area,
It's interesting that the likes of Brembo, who make the porsche GT3 rs race car and R35 GTR 6 pot brakes favour the large area/less pressure idea,
But AP Racing who make WRC brakes favour the smaller area /higher pressure idea!
Makes you thing that there may not be a right answer??
Or am I missing something?
Dan

[STI-ffy]

Another thing, the amount of air in the brake fluid can make a difference under pressure.
Something I learned through bikes so I dont know if its applies to cars.
But if the air is taking out of the fluid before it is out in the reservoir its increases the braking performance under hard use. Something Ive tried and tested, the brakes dont get spongy under heavy braking.

[brocks]

Brake fluid is also hydroscopic, in that it absorbs moisture...this is then converted to air bubbles under extreme braking temps, and can cause "vapour lock" or brake fade, its why you should never re use an already open bottle of brake fluid when changing the fluids.....

Brake pads are a MASSIVE factor IMHO...you can run the best disc/caliper combo with the wrong pads and its like trying to brake with blocks of wood, no feel, no braking efficiency...get the right pads and the amount of bite and feel should improve markably