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)