[s-cars] G60/brake threads... first-order system factors?

[Leigh Anderson]

I tend to agree that fixed caliper system is better than floating (eg
smmmmooooked the rather large floater brakes on RS4 at the 'ring in one lap,
even with ESP turned off.)  however.... all this talk of piston areas, etc
leads me not to calipers but to...

                             rotors,

and specifically their effective cooling area as a first order factor of
brake 'system' effectiveness.  Now i'm not talking about the heat sink value
of rotors, which is pretty much related to mass, i'm talking about their
ability to dissipate heat to the atmosphere at a high RATE to avoid
pad/fluid meltdown/heat sink soak, ie the ability to track Miss Piggy HARD
in 90 degree ambient and have a rock solid pedal/brake capability after a
spirited half-hour+ track session. (even without special brake ducting;
never felt the need.)

That's why i think the 993tt/UrBR ROTOR is the sometimes overlooked GEM of a
braking system component.  You can put a UrBR caliper on a regular rotor
with plain internal vanes but the cooling rate capability i believe is far
less than the 993tt rotor which is the only rotor I know of that has
vanes-on-vanes-on-vanes.  The radial vanes/inside surfaces, have nubs
sticking out and those nubs have nubs. I have no idea how to quantify the
extra cooling area but it may be as much as ~5X the exposed metal surface,
not counting the area of the cross-holes. There may be some additional
'centrigual fan' effectiveness of such a 'super-vane' design. Even with my
2-ton Miss Piggy, I can be a late-braking fanatic, for as long as the
session runs, even on a hot day (R4 track pads and ATE Super Blue).  All due
to the complete UrBR caliper+ROTOR+trackpad+Dot4fluid 'system'. The UrBR
calipers are great, but put them on plain-vane rotors and i'd guess Miss
Piggy would toast them a _lot hotter.

---------------

While I'm on the brake topic, i'll put up some BTDT on the "infamous dreaded
cross-drilled rotors/pads always wears out super fast like a cheese grater
topic."

1. First the data on the front urBR rotors.  The initial set of rotors
lasted me 40,300 miles, from 2/99 until 10/02 (3 years 8 months) and despite
~8-10 hard track days with R4 track pads and much spirited off-ramp etc
street use with Porsche street pads. There were really tiny itty bitty micro
cracks at many of the holes at the end-of-life thickness, but nothing to be
concerned about according to Porsche factory, or so i've been told by oem.
Have used 1 1/4 set of R4 track and 2 sets of street pads, if memory serves.
10/02 I sent the hats back to UltimateG and got back perfectly true-mounted
rotors, no problems, enjoying them now. Ultimate has a ~$12K truing machine
that perfects the mounted hat/rotor combo.

2. Rear 2Bennett cross-drilled rotors also installed at same time/mileage as
fronts, are still going strong. I was too lazy to go take off the wheel
tonite and put a caliper on them, but the wear lip on the edge is about
1/32". Zero stress cracks. R4S compound both street and track.  I'm on 2nd,
maybe 3rd set of pads, with about 1/2 left on current ones.  if memory
serves.

So, the infamous cheese-grater analogy is an urban myth, at least for these
two models of rotors. YMMV for other rotors.  That said, i think grooved
rotor is usually preferable to holes, UNLESS its a UrBR rotor, then the high
cooling rate is the trump card and UrBr rotor is a top choice over most/all
conventional-vaned rotor. I do not defend cross-drill other than these two
specific rotors.

I hope this cheese thing is not too egregious a troll! forgive me if so. (I
reserve right to ignore unsubstantiated-cheese-heads.)

Cheers,
Leigh
UrS4
Quattros Uber Alles!