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

[Robin St.Clair]

Scott
Your reply to Leigh is innaccurate in several
significant points.

The Porsche rotors are not cross drilled, the holes
are cast in, this is described by Porsche, and SHW, as
'pierced' in English - think nipples as an aide
memoire.

The microline cracks between piercings are not a
problem most of the time, its not a fault, its a
physical outcome of being heat cycled. What is a
problem is when cracks run to the outside edge of the
rotor, then its discard time.

Contrary to your assertions, the Porsche factory does
used pierced rotors in race applications, I have some
current season Supercup rotors sitting here (R
996.351.409.9J, R 996.351.410.9J, R 996.352.405.90,
and R 996.352.406.90), additionally I have several
sets of 993 GT1 long distance racing rotors, similarly
pierced. These are all rotors supplied and used by the
Porsche boys - if you doubt me, pick up the phone and
call Weissach, I'll even give you a DDI number or two
if you still have doubts.

If you examine the Supercup cars, you will see that
their brake ducting is by way of attachment to the
lower suspension arms, not through unibody.

Because I have more experience than most when it comes
to retarding large heavy cars from high speeds
repeatedly, I have gone down a path where I have
learned that large mass rotors = peace of mind. I
should point out that I am talking about stopping from
over 200 mph, which is a speed rarely reached on track
days and never reached legally on a regular basis
outside of Germany, so my experience of brake
behaviour under stressful conditions is not typical.
Big rotors and large pad contact areas are what equals
rotor and pad longevity. The problem with ducting air
in a street car is the large cross sectional area of
the air pipe and its consequent ragility in everyday
driving. Experience has shown that anything less than
a diameter of 4 inches is hardly worth the effort.
After some time in a wind tunnel (with a rolling
floor), I hope to have a roadgoing solution.

Given the difficulties of feeding sufficient volumes
of air to the right part of hot rotors on everyday
cars, the high mass rotor/big swept pad area solution
is practical for most cars and their owners.
Once Composite Ceramic brakes enter the picture, the
situation changes as the mass comes down radically.

R+C



__________________________________
Do you Yahoo!?
Exclusive Video Premiere - Britney Spears
http://launch.yahoo.com/promos/britneyspears/