Text 5115, 53 rader
Skriven 2005-01-15 00:46:19 av Dan Ceppa (1:123/666.0)
Ärende: Skidding
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Tech Article Title  Author  Date  
Braking System for Dummies  Leszek Mazur  2001  

Even though a braking system is fairly simple, there is a lot of confusion as
to how it works and how can it be upgraded.  Let us go over exactly as to what
it does and how should one upgrade it. 

A car in motion has some kinetic energy due to that motion.  In fact, the
amount of kinetic energy is proportional to the square of the speed of the
car.  In other words, a car going 60 mph has four times the amount of kinetic
energy than a car going 30.  You all remember the law of conservation of
energy.  When you slow down a car, that kinetic energy cannot disappear, but
has to be changed to some other form of energy. 

The job of the braking system is to change that kinetic energy to heat energy
and dissipate this heat into the air.  Once again notice that the amount of
heat produced by braking from 60 to 0 is four times the amount of heat
produced by braking from 30 to 0. This is why your braking distance will be
significantly longer in the former case.  Let's cover the three most important
elements of the braking system: tires, pads, and rotors.  Tires can exert a
specific maximum amount of force on a car, which is directly related to the
car's lateral g. This force is independent of speed, which is why it doesn't
matter how fast you go on a skid pad when you're measuring the g. The stickier
the tire, the greater the force that it can exert on the car.  Since the force
is independent of the speed, the rate of energy that the tire can deliver
quadruples with each doubling of the speed. 

Pads change the kinetic energy of the car into heat by rubbing on the rotors.
Pads should not conduct heat, so that all heat produced is absorbed by the
rotor instead of the braking fluid.  The larger the friction coefficient of
the pad, the faster the rate of energy that the pad can deliver to the rotor. 

Rotors act as a funnel of energy between the surface of the pads and the
surrounding air.  Rotors should be an excellent conductor of heat and ideally
the rate at which the energy leaves the rotor and goes into the air should be
greater than or equal to the rate of energy arriving at the rotor through the
pads. 

Tires' lockup - we know that rotors were designed to absorb and release the
heat energy produced by braking, tires were not.  During skidding, all the
heat energy is produced not by the pad on the rotor, but by the tire on the
road.  Since neither the road, nor the tire can release the energy as quickly
as the rotor can, the braking distance will be significantly longer when the
tires lock up. 

 

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