Rod:
It seems to me that (almost?) all brakes have enough torque to
lock the wheels. It is the tire / road surface interface that limits the
ultimate braking force. So increasing the torque on the wheel does not
let you stop any quicker. You will have better "feel" so that you can
modulate the force right up to the limit of wheel lock, but past that
there is no gain. When the wheel locks, braking performance stops
increasing (it actually drops) and you are then dependant on the
coefficient of friction and contact patch for your tires.
You also mentioned "stop a car faster in the same distance". I
don't understand your point here. If a car stops is less time from a
given speed, won't the distance always be shorter? Or was this a typo?
Or am I smoking dope again?
Please, nobody answer that last question.
Vance
"Officer, its only for medicinal purposes."
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Rod Anderson
Sent: September 22, 2006 11:51 AM
To: Six Pack
Subject: Fw: general question: Brakes
Third time try at getting this on the list. Apologies for any
duplication....
I think there's a simpler reason that the others presented here. Torque.
To stop a faster car in the same distance, you have to apply more torque
to the wheels. Torque is given by:
T = r x F
where r is the distance from the axis of rotation and F is the force
(both vectors), and x is the cross product (which reduces to simple
multiplication here). So to get a higher T with the same pedal effort
you can either increase F by using pads with a higher coefficient of
friction, or increase r by increasing the size of the pads and rotor.
There are physical or functional limits to the coefficient of friction,
so increasing r is the only option for high performance brakes.
Of course, larger pads and rotors will have greater heat capacity thus
operating cooler than otherwise, but I think this is a secondary
requirement.
Rod Anderson
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