# RE: brakes and lonnnng downhills (longish)

```I can't speak to the exact sizes, but if the UFO's were balanced with the
rears, and then replaced with brakes capable of less work for a given
pressure, then the rears would become dominent, to some degree.  BTW, the
Corvair was supplied with larger rear brakes than fronts, for balanced
stopping under sedate conditions, but addition of a proportioning valve is
useful for serious driving.

This could all be just a front/rear cooling difference demonstration, but
given the slow speed following a large van, I'm not ready to jump on that
bandwagon yet.

kirby

> ----------
> From: 	Chris Newbold[SMTP:cnewbold@transarc.com]
> Sent: 	Friday, October 09, 1998 5:05 PM
> To: 	Smith, Kirby A
> Cc: 	DeWitt Harrison; quattro@coimbra.ans.net
> Subject: 	Re: brakes and lonnnng downhills (longish)
>
> 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
>

```