Brakes and Physics.

[tiAn@usiw.net (Christian Els)]

Go here: <http://www.stoptech.com/technical/> and become enlightened.

These guys make a living at this stuff, and many satisfied customers will
tell you they have it right.

Cheers,


Christian Els
1987 Scirocco 16V, For Sale
www.schnellpc.com/scirocco.htm



----- Original Message -----
From: "Brian McGarvey" <brianm@zbt62.eastnet.gatech.edu>
To: <scirocco-l@scirocco.org>
Sent: Monday, 25 March, 2002 19:40
Subject: Brakes and Physics.


> Ok Folks...
> I got tired of the argument. So I've whipped out the Physics book. Any
> ME's out there or ppl
>
> that are better at ACTUAL REAL non-Relativistic or mumbo jumbo my ass
> tells me... physics
>
> feel free to pop in.
>
> Disclaimer... most things exemplified here are in normal braking
> conditions. ie. you have not
>
> done two footed driving for say 20 or 30 min. or heavy braking to get the
> fluid near the
>
> boiling point.
>
> #1. The brake linings in our cars are better now then ever before. If you
> brakes are turing
>
> to shit. Go buy race or near compound brake linings. You have to replace
> em more often, but
>
> they do work and they make big messes. The race linings will behave more
> like ideal friction
>
> surfaces than most.
>
> #2. There is nothing else at all in the system that can expand or
> compress. Period. As the
>
> volume of fluid gets reduced in container A it goes into the other
> containers ie. your wheel
>
> clynders.
>
> Basic PHYSICS lesson. (yes im on my soapbox)
> A vehicle moving has inertia. It takes the same amount of WORK to stop the
> vehicle in a given
>
> length. ie. F=ma
> if you solve for a then it is a = F/m
>
> the m is constant or very near constant as a small change of less than .1%
> is not going to
>
> make a difference in this calculation.
> So that means that in order to get a larger negative acceleration a larger
> F is required.
>
> Assumption. Your tires are not crap. Your tires are relatively sticky. ie
> they have a decent
>
> coeffienct of friction and maximum force point before they turn to
> dust/liquid/gas.
>
> so now you are trying to increase the force to increase the negative
> accleration. no mind you
>
> were are still living in the linear force section of the friction curve.
>
> (FORCE lesson)
> IF the force applied to the disc is constant. the ONLY method for
> increasing the torque
>
> applied to the rotating mass is to increase the distance from the center.
>
> If you want to increase the force in the exsisting caliper and disc you
> basic choices are.
> -- depress the pedal farther but past the point where the master clyn is
> empty.
> -- increase the lever arm of the pedal (less force by you.)
> -- move a larger volume of fluid. ie a larger master clyn diameter and the
> same bore length.
> -- longer bore length (more pedal travel) same diameter
> -- or a combination of increasing bore diameter or length.
> -- this whole master clyn description basically boils down to more volume
> in the master clyn
>
> so now you know that to get more force with the same pads, calipers, and
> discs it takes a
>
> bigger master clyn to get more force.
>
> What does increasing the size of the rotors/discs do?
> by using the SAME size calipers on a larger diameter disc with the same
> CONTACT patch. ie.
>
> the Force being applied to the brakes using the same master clyn and
> caliper are the same,
>
> but the distance from the center of the disc is now longer. so now with a
> little simplified
>
> physics magic. Im sure the ME's here will expand on the physics.
>
> so there..
>
> and fade can occur for several basic reasons.
>
> * the amount of force at the wheel decreases due to losses in the system
>   -- ie. the master clynder hits the stops and has no more volume of fluid
> to press.
>      -- losses can be due to a leaky master clyn, leaky wheel clyn.
>      -- the rubber hoses expanding enough to lower the volume of fluid
> transferred to the
>           wheel clyn there by reducing the force applied.
>
> * the coefficient of friction decreases at the disc/lining interface.
>   -- get better pads.
>   -- cool the system.
>
> * the coefficient of friction decreases at the road/tire interface.
>    -- drive on better roads <VBG>
>    -- get stickier tires... and no complainin' metzler
>           ME-1 CompK's last 1500 - 5000 miles(not a miss print) and are
> 150 - 200 a Tire.
>   but hey you can leave a thumb print in em after riding around
> the block.
>   they actually pick up loose dirt. Ive gone thru two sets in a
> riding season before
>
> ________speculation below ________________
>
> does improving the front brakes alone make a difference.
> I suppose its time to try it out.
> we'll have to have everybody with all the diff combinations all get the
> same pads.
> change em. and bed them in properly. verify that all brake systems work
> properly.
> and do panic brake tests on the runway measuring distance. with different
> drivers swapping
>
> cars.
>
> but my prediction based on the number of times ive panic braked on
> motorclcyes where i get to
>
> actually modulate the rear brakes seperately from the front is that as
> long as the rear
>
> brakes are adjusted properly according to the bently the larger brakes in
> the front will
>
> decrease the stopping distanc.
>
> make more passes
>
>
> brian
>
>
>
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