cross drilled rotors [Round Two]

[Larry" <rocco16v@netzero.com (Larry)]

Jason-
----- Original Message -----
From: 16V Jason <jason@scirocco.org>
To: Brian McGarvey <brianm@zbt62.eastnet.gatech.edu>; Brett Van Sprewenburg
<brett@netacc.net>
Cc: <scirocco-l@scirocco.org>
Sent: Monday, March 25, 2002 12:17 PM
Subject: Re: cross drilled rotors [Round Two]


> At 09:06 PM 3/23/2002, Brian McGarvey wrote:
>
> >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.
>
>
> Uh, Brian, all that is true and all, but the largest contributing factor
to
> fade is indeed not stretch in the brake lines due to heat, it's the loss
of
> the brake pad's coefficient of friction at high temperatures.
>
>
> >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.
>
> Yes, which will likely stiffen up the pedal -- but roast the pads, and
> it'll be stiff but useless.
>
>
> >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.
>
> That is very true -- but that brings up a great problem, which is the
> reason I'm jumping in here.
>
> So, we are all agreed that having a larger rotor with a caliper positioned
> further out from the center of the hub would, all other things being
equal,
> provide more braking per unit of pressure applied to the pad.  The two
> brakes will generate the same amount of heat by the way, regardless of how
> far the caliper is from the center of rotation, since they're both
stopping
> the same mass.  We're also agreed that, again all other things being
equal,
> the larger rotor and caliper would be able to absorb and dissipate this
> heat better than the smaller.  Agreed.
>
> But look what you just did -- you increased the braking on the front end
of
> your car for every pedal pressure.  You helped to eliminate brake fade on
> that axle as well helping ensure that this increase in braking force
> continues even at high temperatures.
>
> But you didn't do shit to the rear axle, did you?
>
> So what you did was tilt the car's front/rear brake bias further towards
> the front.  You just *increased* your braking distance.  Say before your
> brakes were proportioned "ideally", meaning that you were able to easily
> hold all 4 wheels at impending lockup.  Now, you'll be able to keep the
> fronts at impending lockup, but not your rears.  Regardless of how badly
> your brakes were proportioned in the first place (unless you had a
> rear-bias, which you don't or you'd be dead), you have just increased the
> maximum braking distance of your car.  Sorry, that 11" brake conversion
> just cost you your insurance deductible.
>
> OH!  Wait!!  Something else just popped up!  Since we all know that you
> will get your best braking at impending lockup (hence the reason
> ABS-equipped cars that keep all 4 wheels at/near impending lockup under
any
> conditions stop more quickly almost all the time), we know that we have to
> modulate our brakes to keep them on the edge.  But since the pressure
> exerted on your brake pedal is now amplified more, modulation becomes even
> more difficult:  A smaller difference in pressure on the pedal now defines
> the difference between impending lockup (100% braking ability) and full
> lockup (only about 80% of full braking ability).
>
> So not only did you increase your theoretical minimum stopping distances,
> you also made it harder to reach that theoretical minimum.
>
> And at the same time, you increased unsprung and unspring-reciprocating
> weight.  That means your car is now slower, handles worse, and doesn't
> brake as well.  COOL!
>
> :)
> Jason
>
>
>
> modulation
>
>
>
> >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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> >
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