Re: brakes and lonnnng downhills (longish)

[Chris Newbold <cnewbold@transarc.com>]

Smith, Kirby A wrote:
> 
> The analysis below of Chris', which I feel cannot be easily culled to limit
> BW, is a good one, but skips one important step.  Given that the hydraulic
> pressures are equal, the piston force equals the piston area times the
> hydraulic pressure.  The pad force, for infinitely stiff pads, equals the
> piston force.  So, assuming no lockup, if the rear pistons are larger than
> the fronts, there would be more work done at the rear than the front, if the
> pads at each end are the same distance from the axle centers.  (Work = force
> x distance).  So, we need piston sizes and radii to the pad centers to
> continue this.  Of course, the real question is which end locks up first.

Yeah, yeah, yeah. I purposefully ignored these "details". I believe in
general, that you'll almost always find more piston area up front: larger
pistons, dual pistions, etc. My simplifying assumption was that front
brakes are typically more powerful than rears because, given the forward
weight shift during braking, you can almost always do more "braking work"
up front...

If this is true, it is the opposite of what we'd need to explain Phil's
observations.

In fact, I believe I remember Phil saying that the UFO conversion he has
uses the G60 calipers. These have two pistions, one slightly larger than
the other.

-Chris