Self correction!
I used 15/14 but of course the actual rolling diameter could be more or
less, depending on tyre aspect ratio.
..anyone for 23/22 = 4.5%

Sorreeee!

----- Original Message -----
From: "Clive Smith" <clive.harman-smith@NTLWORLD.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, November 07, 2002 2:12 AM
Subject: Re: Drilled Rotors vs. Big Brake Kit

> Slight correction..
> >Braking force for this instance is the torque
> applied to the axle by the brakes multiplied by the distance from the hub
to
> the center of the pad.<
>
> Thats a torque multiplied by a distance
> Ft-Lbs-Ft = Ft ^2 Lbs - wrong units for force, should be lbf only!
>
> Braking force = braking force (presumably you mean at the centroid of the
> pads)
> Braking torque = braking force multiplied by the distance from the hub to
> the center (centroid) of the pad(s)
>
> But all you have to really do is use similarity and multiply the original
> braking force by the ratio of the New wheel diameter by the Original one.
> Easy!
> Fnew = Fold * Dnew/Dold, so if the new calipers are the same distance from
> the hub centre as the old, we have a 15/14 or 7% greater requirement, but
as
> the wheels themselves contribute to momentum (angular in this case), as
> discussed exhaustively a month or so ago, the requirement is even greater
> (when increasing wheel size).
>
> Suffice to say that since I often carry a ton or more of
earth/sand/ballast
> in my Syncro, which has 15" wheels, regardless of the debate, I know a set
> of solid ventilated SA discs and calipers I've ordered are going to make a
> difference - if push comes to shove - which I hope it doesn't too often. I
> also happen to think that the standard T25 brakes are pretty good and if
> yours aren't, then take a good look at them - the usual problem is
thinning
> discs and non OEM cow-dung pad material - same goes for Italian cars, put
> Lancia pads on a Lancia and it stops, even down a steep hill from 100 mph
+;
> put any others on and I wouldn't be too sure (speaking from a near death
> experience). Don't mess with tyres and brakes, use the best - they're
you're
> interface with the road effectively. Money well spent. I suspect the
drilled
> discs with metallic pads are an effective economical replacement option,
as
> for one, they'll be new!
>
> Clive
> '88 Syncro Transporter
>
> ----- Original Message -----
> From: "pensioner" <al_knoll@PACBELL.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Wednesday, November 06, 2002 10:52 PM
> Subject: Re: Drilled Rotors vs. Big Brake Kit
>
>
> > The engineering reason for the SA large brakes with the 15" wheels and
> > larger tires has to do with the "effective" braking force.  Larger
> diameter
> > tires require a proportionately larger retarding torque on the wheel to
> > generate the same stopping force.  Putting 215x75-15 tires on a standard
> > syncro westy produces a loss of stopping power as the braking force has
to
> > work through a larger "moment arm" (distance from axle center to road).
A
> > few definitions help here:  Braking force for this instance is the
torque
> > applied to the axle by the brakes multiplied by the distance from the
hub
> to
> > the center of the pad.  Stopping force is the force generated at the
road
> to
> > tire interface that actually declerates the van.
> >
> > For a given braking system increasing the tire diameter will decrease
the
> > stopping force.
> >
> > To compensate, VWSA added more braking force via a larger disk and
caliper
> > assembly.
> >
> > Drilling rotors actually has very little effect in terms of increasing
> > braking force.  It does allow slightly better cooling over the solid
> rotors
> > and slightly bettter wet performance.  The SA vented rotors are far
> superior
> > in terms of heat dissipation characteristics than the smaller solid
> rotors,
> > drilled or not.  Drilling can postpone brake fade but not really
increase
> > the braking force by any significant amount.
> >
> > The pad to disk interface describes a cylindrical swept area on the disk
> > itself.  This interface generates heat and the function of the pad is to
> > continue to provide contact friction as the temperature of the interface
> > rises.  At some elevated temperature the pad material will break down
and
> > exhibit a "glazing" or "carbonizing" characteristic that has a poorer
> > pressure to friction coefficient.  For the same pad pressure the failed
> > material produces significantly less friction and therefore less heat.
> The
> > heat being dissipated by the thermal mass of the disk and its
> configuration
> > is how the energy of motion of the van goes from kinetic to heat slowing
> the
> > van.
> >
> > Are you listening, Dr. Feynmann?  How'd we do?
> >
> > "fizzix, it's always just fizzix"
> >
> > pensioner (start slow then taper off)
> >