[s-cars] [urq] S-Car Brake system conversion- Read- no more PSpumpintegration <question>

[Keith Maddock]

It helps to do a force schematic using a sectional diagram of each caliper.

In a sliding caliper, the back of the piston chamber acts essentially
as a 2nd piston, because its movement is only resisted by the forces
of the caliper bridge acting on the brake pad / rotor on the other
side.

This is why a sliding caliper has twice the force for the piston
diameter, compared to a fixed caliper.

That said, the G60 still has a larger effective piston area than the "Big Reds".

Therefore, with a Big Reds, more pressure is needed for the same
clamping.  However this is fairly well negated by the larger rotors
usually associated with a BBK upgrade.

Greater pressure would imply more brake fluid volume displaced,
however, this is fairly well negated by the stiffer bridge of the Big
Reds.

The only car that I had before/after with was my 93 S4, and I can't
say that the brake feel significantly changed after the Big Red
conversion under normal braking, the big difference was the
significantly improved fade resistance.
This was with the smaller 314mm rotor upgrade, if you used a larger
rotor, you'd feel stiffer brakes as you had to generate less caliper
pressure, and therefore less displacement, for the same stopping
force.

YBMV*, and heck, I'm not even an engineer anymore :)

----------------------------------------------------
Keith

*Your Braking May Vary


On Sat, Mar 21, 2009 at 22:09, Mark Strangways <MarkS1234 at spamarrest.com> wrote:
> I don't agree with your way of thinking.
> I have been in hydraulics for about 20 years now, and pressure apllied
> by opposing piston on a clamping surface is the sum of each side.
> If fact you may say that on a sliding caliper, the effective clamping
> force is shared between each side.
>
> The reason the pedal travel is less with a fixed caliper is that each
> piston moves less than that of its G60 conterpart, while imposing
> twice the clamping force.
>
> Result less pedal travel, twice the pedal resistance... And that is
> exactly what I found going from G60's to 996 TT calipers.
>
> (Flame suit on)
>