Re: Multiple-calipers on touring cars

["Sokoloff, Jim" <Jim-Sokoloff@xxxxxxxxxx>]

> However, what is there to be gained by having that much friction area?  We
all
> know from College Physics that it is the force that we apply to the
surface is
> what that matters.

True. So far so good, but you're about to have an off-track excursion... :-)

> Besides, if you cover up the disc area with a caliper,
> there's less room for heat to dissipate!

But, most of the cooling in vented rotors is from air being pulled (or
forced for track cars) through the center of the rotors anyhow...

> If I went to twice the number of
> pistons, and increased the clamping area by, say 1.25, I would then lose
1.25
> the amount of force at the pistons given that I apply the same force at
the
> pedal.  I.e. to stop the disc the same amount, I would have to apply 1.25
> times more pedal pressure due to my 1.25 increase in surface area.

Nope. For a constant force applied to the brake pedal (ignoring any servo
assist for the moment), and a constant sized MC, you will generate a
constant PRESSURE in the brake lines.

Apply that constant PRESSURE over a larger caliper piston area, and you'll
get more FORCE applied to the pads. 

Of course there's a downside to this, which is the pedal travel will
increase by the area ratio. (The pedal will travel 1.25 times as far in the
above example, but the clamping force would be higher...)

> Bummer.  So to compensate, do I need to *reduce* the master cylinder size?


If things were actually as you described, then yes, you would, but since
they're backwards, you would need to *increase* the MC size...

- ---Jim

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