braking question

[Lawrence Weeks]

Once upon a time (Mon Sep 08), Slamtry wrote:

> I have been told enough times by people whose intelligence I
> respect that a car achieves its best braking performance NOT when
> the wheels are locked up, but at some point before that. I have
> never understood this. It seems to me completely counter-intuitive,
> but let it go.

Ever take physics? The car has mass, and a velocity: energy. This is
all about energy. As the car slows down, it must lose that energy. That
energy is converted to heat, mainly. The car slows by using the
friction of the tire against the pavement, generating heat. To slow
the motion of the tire, and consequently the car, your brakes also
use friction and absorb heat. That is the energy of your vehicle
being dissipated.

What if your tires are locked? At that point, the tires are not
turning, the brake rotor is not turning, and the brakes, designed as
heat sinks, are not absorbing heat. Instead, your tires, designed to
grip the road, are being ripped apart due to the friction between the
road and the tire in a single place. The tire is not turning, fresh
tire is not being used. The tires are heating up, the air inside is
expanding. The tire is taking structural damage.  Meanwhile, the car,
rather than slowing down in a controlled manner, is now sliding. There
is a layer of destroyed tire material (not really rubber) between the
tire and the road, reducing the effectiveness of the tire in slowing
the car through friction.

> Given that my stock brakes on my Classic will lock the brakes up,
> how is that the NX2000 upgrade will help me? After all, if optimum
> braking is achieved at just before wheel lock-up - and my current
> brakes will lock up the brakes very fast indeed - ...

By themselves, the larger brakes will not help your car stop
faster. Not much. They have a larger pad, and thus more area over which
to transfer energy faster. The main factor in stopping distance is your
tires. Wide, sticky tires, will produce more energy through friction
with the road faster, stopping the car faster. Larger brakes will
be capable of absorbing & dissipating the heat faster, maintaining
the efficiency of the process. Better pads better grip the rotor
(more friction), while not generating a gas barrier between.

If you have narrower, less sticky tires, then odds are your current
brakes are fine.

Larry
--
Lawrence Weeks                                    lweeks@anabasis.net
Anabasis Consulting Ltd