cross drilled rotors Scott Williams is WRONG!

[brianm@zbt62.eastnet.gatech.edu (Brian McGarvey)]

my two cents here

Engineer (electrical) with LOTS of physics background.
Brett is 99.99% right
yes our brakes basically turn KE to heat, but there is alittle additonal
physics going on too.

(please note this first bit is for ppl on the STREET)
Most pp here are concerned with upgrading ther current brake system
because of worn parts etc. A few are concerned because they have
experienced brake fade.

In our cars and most other cars out there we experience brake fade because
the fluid in our brake systems becomes very hot. THis inturn heats up the
rubber elements in our systems. Agruing about which brake master clyn to
use for what pressure required is pointless at this point.

basically the brake system works like basic hydrolics. The brake fluid is
a high boiling point incompressable fluid (and you engineers out there
know that the tiny tiny amoun that it does compress is irrelavent). so you
have a large volume of fluid occupying some space that space is removed by
depressing the brake pedal moving the master clyn pistion. THis FORCES the
fluid out of the master clyn. it has to go somewhere. So it goes to the
wheel clynders which EXPAND if the is no other expansion in the system.
Under normal operating conditions and when the rubber hoses connection the
hard line to the brake caliper are fairly new and you havent bee giving
your brakes a workout heating the fluid and thereby heating the rubber
hoses. So in the case where youHAVE been giving the brakes a workout. THe
rubber hoses going to the calipers in the front ant the two hoses
connecting the hard lines in the back have now become heated and now ALSO
provide a point in the system for the fluid FORCED out of the master clyn
by YOUR FOOT to go. Basic brake fade occurs when the rubber hoses are
expanding enough so that the wheel clynders do not move as much as
desire or at all picture a baloon at each wheel. THis is due to HEAT.
THese tepereatures occur well below the boiling point of the brake fluid
so the brake fluid is STILL and incompressable fluid.

So now here is when you want to upgrade to Stainless steel braided lines.
basically all you are doing is removing the baloons at each wheel.

Next now you think you have solved your brake fade problem
Not true. you have only delayed it. Normal brake fade occurs due to the
expanding rubbber hoses the effect is usually gradual and tells the driver
to take it easy until the temp comes down a little. with stainless lines
you konw move into a more dangerous realm of brake fade liquid
vaporization. THis is why all the racers use the REALLY hight temp brake
fluid. because what happens is you go from good brakes to ZERO or near
zero brakes  as the temp rises enought to boil the brake fluid in the
calipers. THe fluid goes thru a state change from beingand incompressable
liquid to a VERY compressable GAS.  good brakes good brakes... shit no
brakes.

SO as you can see before you upgrade anything else you can see that
cooling the brake system is of the upmost importance. THis is why on an A2
GLI the little  holes in the spoiler with the plastic funnel compresses
the air and directs it at the front disk brakes -- adding some cooling.


Nw the little problem of effieciency(sp) comes in.
For the same amount of work (moved fluid) having a longer lever arm
provides more torque. DOnt belive me. What about your front wheel axle
nuts. while brakeing does turn KE into heat there are more effienect ways
to do it so you get less heat. (you thermo ppl can help here). (my
connection is startign to suck again so typos will start up again). SO if
you still have the problem of you want to stop quicker and your tires are
NOT sliding if you are sliding.. get BETTER tires or stop pressing on the
brakes so hard. as the tire starts to slide your coefficent of friction
goes waaaay doen its very inefficeint. a sliding stop takes as much as 50%
longer to stop in as a non sliding stop all things being equal.. thats why
new cars and some motorcycles have ABS brakes. . increasing diameter adn
the swept area remaining constant will result in less heat or equal heat
generated. Increasing the swept area
will integrate the heat over a larger area overall reducing the average
temperature.

Holes and slots. <-- in some extreme conditions they may actually help.
but getting larger dia disks with holes or slots is still better than
smaller ones. (more swept area lewer temp not less heat).

tired of hearing this argument... rage for days.
basically slots and drilled rotors unless you are RACING for long periods
of time or in extreme conditions (mud, snow, rain, desert) it deos do
shit. So there.
no vented vs. not vented is an easy one. more Surface area  means more
convection. means lower temperature NOT lower heat. you basically dOuble
the surface area and increas the mass of the rotor so yes that is a good
upgrade. but if you drive like my wife or an old lady ... dont bother.
unless you wanna look cool.....or they come on the car already installed
by the PO... <-- my case!

brian
2.0L Topless bunny
Brakes.
Stock booster -- bad sticky brake pedal syndrome manual return often
required
Stock master clyn new
10.1's in the front zimmerman xdrills PO of 16v bought them
drums in the rear
one new wheel clyn in the rear.


On Sat, 23 Mar 2002, Brett Van Sprewenburg wrote:

> >Bigger rotors do give the caliper much more leverage to work against
> >the spinning wheel. You can easily set up your own experiment with a
> >spinning bike wheel and see what I mean. What do you think is easier
> >to grab and stop, near the hub or near the rim? Also the rotor and
> >pad material used in F1 is so exotic we cant even begin to relate a
> >tenth of the physics going on there and apply it to our street cars.
>
> I'm going to scan the article now, as I just can't stand this
> anymore..The physics of
> turning kinetic energy into heat works exactly the same between our
> cars and an F1 car.  You are of course correct that
> they can use exotic materials to increase their heat handling and
> transfer...you are also correct that it's easier to stop
> something spinning near the rim, then near the center.  Here's how to
> generate the same effect with a smaller rotor:
>
> Press On The Brake Pedal Harder.  No kidding. :)  In other words
> create higher clamping load, which may generate more
> heat, but then we're back into the heat issues previous discussed.
>
> Once you reach the point of tire lock up (and if you cannot, then you
> DO need brake work) you will NOT generate any
> more braking force, no matter how far 'out' your caliper is away from
> the hub.  Just physics.
>
> >
> >While watching some Tarmac rally last year I remember in a tech
> >sidebar they were talking about putting the largest brakes they
> >could fit under the wheel in order to cope with the extra braking
> >needed. I put more stake in a WRC engineer than a guy racing most
> >anything in the US let alone a Saturn.
> >
> >Jasin
> >one cents worth
>
> That 'guy' racing a Saturn is (as I wrote) an engineer creating
> braking systems for the Robert
> Bosch corporation (we've all probably heard of them) and I only threw
> out the fact he was
> also a racer as a point to his practical experience.
>
> Yes, this is info on how braking actually works can be suprising and
> offensive, as it upsets
> several beliefs and notions we (including myself) have had...
>
> ==Brett
>
>  \/  '84 Scirocco (ITB racer 2B) | "Hot VW's, take two home. They're small"
> \/\/ '88 Scirocco 16v (Show), '92 Passat 16v (Winter+) | - brett@netacc.net
>
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