[s-cars] RE: [s-list] Nose-down brake diving

[Richard Tanimura]

This is a multi-part message in MIME format.
--
[ Picked text/plain from multipart/alternative ]
Hi Hap,

Well, unless my physics are completely wrong, the mods won't be very
effective. I don't mind being wrong though, you learn every time you are.

You're an engineer. So lets see where our thinking on this diverges.

Thought experiment 1: If you had no front brakes at all, only rear brakes,
would the car dive when you applied them? The answer is an unequivocal yes.
This is the heart of the whole matter. Again, I suggest Fred Puhn and/or
Carroll Smith. They make this all clear.

Stiffer springs in the front work to reduce dive. Yup. The weight transfer
in lbs. is exactly the same, of course, but the the dive in inches is
reduced since spring constants are lb/inch. Stiffer spring = more lb/inch =
less dive. We are on the same page here aren't we?

Thought experiment 2: Would you get dive if you replaced the springs and
struts with solid metal pipes? (Hint: Think infinite spring constant) Nope.
But you would load your tires so hard you would have a contact patch the
size of Rhode Island.

We have to break down the causality chain. Braking, front or rear, induces
transfer. Tranfer causes dive. Dive affect tire wear because the kinematics
of the front suspension change camber and toe. To improve tire wear you can
attack any or all parts of the chain. You can:

    Brake less hard - but none of us will including me

    Reduce transfer - reduce total weight, lower the CG, change geometries
so the pitch axis is closer to the CG

    Reduce dive - stiffer springs,

    Reduce camber and toe change - buy the worlds best front suspension with
bump steer compensation and the whole shooting match. (By the way, I bet
BB's car is     lowered which would also affect his suspension kinematics)

Rich

  -----Original Message-----
  From: CaptMagu at aol.com [mailto:CaptMagu at aol.com]
  Sent: den 27 april 2003 17:26
  To: Richard at Tanimuras.com; thecyberpoet at cyberpoet.net; russ at s-cars.org
  Cc: s-car-list at audifans.com
  Subject: Re: [s-cars] RE: [s-list] Nose-down brake diving


  Richard

  With the forward weight CG that the urS-car has to carry there is a severe
penalty to be paid with too much reliance on Big Front Brake upgrades. That
is why several of us in Colorado are persuing a rear Big Red upgrade as
well. In order to properly tune this setup I will be installing a brake bias
control to prevent trail brake oversteer. My upgrade will consist of the Big
Reds and 314mmx30mm 2 piece rotors.

  I also have the new 2Bennett camber/caster plates which will allow me to
install front coil-over to match up with my rear coil-overs. The front
coil-overs along with custom valved Bilsteins will also help to battle the
hard brake dive.

  My good friend Brian Billottti is running a 350 or 355 mm Front Brake
upgrade with Brembo 6 piston calipers. His dive with these brakes has
actually affected his tire wear at the track. As you load that front
suspension you do increase your negative camber and he's noticed the inside
tire wear increase since he installed those huge front brakes. Brian will of
course be stealing from the CO crowd once again as this mod gets done.

  Hap, moddin away in Everboost, Maguire


--