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Physics of braking (long!!) RE:corrado brakes
Not much of an expert on brakes, but having taken way too much physics in
college, I feel compelled to respond.
There are a multitude of facets involved in making your car stop.
Let's start with the tires. The tires are kept stationary (although
rotating, the surface of the rubber, for all intants and purposes, does
not move with respect to the ground) during braking because of the
friction between the ground and the rubber. The maximum force that the
tires can deal with before breaking loose/locking up is determined by
the static coefficient of friction (SCF). The SCF is a unitless number
and the way that the maximum force to the road is determined depends on
the downward force (weight of car) with which the tires are contacting
the road. So the stopping "power" that the tires supply depend on the
SCF of the tires, and the weight of the car.
Still with us? Good
On to the rotors and pads. The reason that the tires are experiencing a
force against the ground is (mostly) because of the friction between the
brake pads and the rotor when pressing the brake pedal. But here there
is constant motion, so we are dealing with the kinetic coefficient of
friction. The KCF is also dependant on the force with which the pads are
contacting the rotor. Now if the force created between the pad and rotor
(as felt at the tire) is greater than the maximum friction that the tire
can withstand against the road, you will lock up the tire. And the KCF
of the tire to the ground is less than the SCF of the tire to the
ground, so you will stop slower.
Rotor size: The bigger the rotor is, the smaller the required force
between the pad and rotor to provide the same frictional force to the
ground. This means longer pad life, cooler rotors, and less fade (the
phenomenon that the KCF of the pad to rotor decreases at very high
temperatures)
So it seems as if though the only thing significant is the SCF of the
tire to the ground (assuming that you can lock up your wheels). The
stickier your tires, the quicker they will let you stop.
So, assuming that the tires and brakes are identical, how could Al Unser
Jr. outbreak all the other drivers?
Technique. The quicker and closer you can get your brakes to the most
efficient braking, and keep that friction applied without locking up
your brakes, the quicker your car will slow down.
So are the corrado brakes better?? Well, assuming that they give you more
control, you can then make better use of the tires ability to stop your
car. That, and their increased resistance to fade, are key factors.
But if you are happy with the control you have of your current brakes,
and don't have a problem with fade, then increasing the rotor size is
IMHO a waste of money.
HTH
Jonas
85 Scirocco
PS. Did that feel like a physics lesson, or what.
Shawn C Meze wrote:
>
>On Thu, 04 Feb 1999 16:45:13 -0500 16V JASON <jason@scirocco.org>
>writes:
>
>>True, the increase in swept area will give the brakes more
>initial
>bite..
>>but (and now we come to my point), isn't the braking distance of
>a car
>>limited essentially to the tires' ability to grip? I mean, I'm
>sure I
>>could do 200 km/h (125mph) in my 16v and lock my front wheels up
>instantly
>>(not that I would want to, of course)... so what good would
>bigger
>rotors
>>do? If the rotors can overpower the tires (which they can, if
>they can
>stop
>>the wheel from turning), what's the point of having bigger
>rotors?
>
>
>True, the tires ability to grip can be the limiting factor in the
>cars
>ability to stop. However a skilled driver will know how to make
>the
>brakes work to their fullest without locking them up. Need I
>refer to the
>CART series as an example? Al Unser Jr. was famous for being able
>to
>outbrake the competition going into a turn. Nuff said, point
>made.
>
>
>
>>So, with that said, and thus neglecting the fade factor, what's
>the
>benefit
>>of upgrading to 11" brakes? As far as I can see, the only
>benefits are
>>fame (people saying "You're cool!"), and that's surely
>outweighed by the
>>cost (ouch) and the increase in unspring weight.
>
>
>Bigger is better in the braking world. Ive driven/ridden in a car
>with
>11" brakes and -damn it-, it just stops. I want those so I can be
>the
>first to -ever- make them 11"s fade! <Drool>
>
>
> Shawn Meze
>86' Jetta GLi 82' Scirocco GTi
>The Fastest, Quickest, Cleanest and
>best looking Scirocco in all of San Diego!
>http://www.Geocities.com/MotorCity/Speedway/1308/index.htm
>
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>To: jason@scirocco.org
>Cc: scirocco-l@scirocco.org
>Subject: Re: Corrado Brakes -- Physics Question: Are they
>pointless?
>Message-ID: <19990204.152655.9119.1.Skerocdriver@juno.com>
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