Date:         Mon, 21 Jun 2004 00:53:14 -0400
Reply-To:     Kim Brennan <kimbrennan@MAC.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Kim Brennan <kimbrennan@MAC.COM>
Subject:      Brakes (upgraded and standard)
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I was giving some thought on a drive home late Saturday to the issue of
brakes. The few folks that have actually upgraded to the "big brake"
kits haven't had really definitive comments on whether they allow you
to brake "better. This is not what this posting is about however.

Braking is, in essence, a way to transfer motion energy into heat
energy. it does this by the mechanical application of calipers (and
brake shoes) to the front discs (primarly, but also to the rear brake
drums). The resulting friction of the brake pads/shoes against the
discs/drums results in the generation of heat. In time it also slows
the vehicle down. However, now you have hot discs/drums.

In order to improve your braking capability, then, you need to do at
least one of the following, increase the clamping force, increase the
friction factor, increase the transfer of energy (heat) to the
destination (discs, shoes).

The Big Brake kits, primarily attack the last two items. The friction
factor is increased (marginally, in my opinion) by having a larger wear
area (larger diameter disc). The transfer of energy is increased by
adding more mass to the discs and adding ventilation to the discs
(meaning they can accept more heat in, as they in turn can transfer it
to the air faster. )

Note that cross drilled discs (frequently available in high end sports
and sporty cars) add increased ventilation with the cross drilling,
with a slight loss of mass of the disc. I presume that they have done
sufficient testing to notice a gain  in the heat transfer with the
added ventilation despite the loss of mass. Since there is also,
however the added benefit of removing unsprung mass (increasing
acceleration performance) there may be a separate compromise decision
impinging on cross drilling.

Of course, this is all just 2am rambling. The type of discussions that
geeks have way too late at night...