cross drilled Scott Williams is YOUR DADDY!

[scirious@hotmail.com (Brian Haygood)]

Your equations says that bigger brakes have more stopping power per unit
normal force.  It doesn't say that your car will achieve a shorter stopping
distance than it otherwise would because your wheels will lock up when the
same equation limits traction between your tires and the road.  Unless you
overcome that weakest link, then you will never have a use for that extra
stopping power, in just the same way you never use it now.

Now the real question is how you managed to pull that equation out of your
ass.  The friction force is not proportional to the surface area.  F=uN, not
F=uNA.  Now this equation is an estimate as well, and is really only
accurate so long as the yeild strength of neither of the parts in contact is
achieved (give or take).  This is why more rubber on the road means more
traction, because the tire crumbles just like a pencil eraser before it can
transmit its maximal force dictated by its static coeficient of friction.
But even this relationship is generally miles away from creating a
proportional relationship between surface area and friction force.

The larger area means the same amount of energy can be dissipated with a
smaller increase in temperature over a larger mass of metal.  So they don't
heat up as much.

The disadvantages of larger brakes, including increased vehicle weight,
increased unsprung weight and its associated traction loss, increased
rotational inertia and its acceleration/deceleration losses, have already
been discussed in this thread, so I don't think we need more words to say
that if there isn't a strong need for bigger for heat reasons, then smaller
will be better.  Again, we have to realize that these are lightweight cars,
and therefor react more poorly to an extra pound of unsprung than the
heavier A4's and such.  Heat can also be reduced with vented rotors, which
usually (IMO) offer weight or rotational inertia advantages over their
larger rivals that could handle the same amount of energy (heat).

There is a bit of friendly ribbing in there, and I hope it is taken as such.

BH

----- Original Message -----
From: Aireq <trance_whore@yahoo.com>
To: Scirocco Mailing List <scirocco-l@scirocco.org>
Sent: Saturday, March 23, 2002 3:36 PM
Subject: RE: cross drilled rotors Scott Williams is WRONG!


> F = uNA
>
>
> Force of friction is equal to the coefficient of friction, times the
normal
> force, times the surface area. Bigger breaks will stop faster. Simple
> physics. But the question is where the trade off goes the wrong way in
terms
> of weight added vs stoping power.
>
>
> aireq
>
> -----Original Message-----
> From: scirocco-l-admin@scirocco.org
> [mailto:scirocco-l-admin@scirocco.org]On Behalf Of ATS - Patrick Bureau
> Sent: Saturday, March 23, 2002 10:47 AM
> To: Brett Van Sprewenburg; scirocco-l@scirocco.org
> Subject: RE: cross drilled rotors Scott Williams is WRONG!
>
>
> Bret I would agree for road vehuicules and daily drivers, coudl you
explain
> why then F1 Racing and Nascar Use Cross drilled rotors if indeed it
provide
> "now-adays" no evidance of added performance.
>
> inquiring mind would like to know.
>
> ATS - Patrick
>
> =>-----Original Message-----
> =>From: scirocco-l-admin@scirocco.org
> =>[mailto:scirocco-l-admin@scirocco.org]On Behalf Of Brett Van Sprewenburg
> =>Sent: Saturday, March 23, 2002 12:12 PM
> =>To: scirocco-l@scirocco.org
> =>Subject: RE: cross drilled rotors Scott Williams is WRONG!
> =>
> =>
> =>>Hehehe that got your attention ;-)
> =>>
> =>>I don't know about performance, I think everyone is missing the point.
> =>>Rotors have holes drilled into them in order to increase air flow,
> =>>thereby reducing heat in hard driving conditions (such as racing on a
> =>>track). That's the theory behind that. I would say (not from experience
> =>>since my car isn't done) that they would work...It just makes sense.
> =>>Will this increase performance? I don't know, but I do know they would
> =>>have to be cooler (temp) no? Of course it could take a couple of
seconds
> =>>for the pad to grab the cooler rotors (so I've heard). That's why you
> =>>would want to get the braided lines to get a better bite in the
> =>>caliper...As far as Scott being wrong, I think I have a better chance
on
> =>>finishing my car today than proving him wrong...
> =>>
> =>
> =>I really need to post that brake article... :)
> =>
> =>Anyway,  I'm afraid the above opinion is incorrect.  I'll paraphrase
from
> =>the GRM brake article again...
> =>
> =>Crossdrilling your rotors does nothing in most situations
> =>now-a-days,  except
> =>look cool...so please don't say it's for higher performance. (And
> =>they do look cool) ;)
> =>
> =>Rotors were first drilled because early brake pads from the 40's
> =>and 50's gave
> =>off gases when heated to racing temperatures.  The gasses then
> =>formed a thin
> =>layer between the brake pad face and the rotor, acting as a lubricant
and
> =>lowering the coefficient of friction.  The holes were implimented
> =>to give those
> =>gasses someplace to go.  Todays friction materials generally do
> =>not exhibit
> =>the same gassing out as the early pads.
> =>
> =>The holes have carried over more as a design feature than a
> =>performance one.
> =>Contrary to popular belief, they don't lower temperatures.  In fact,
> =>by removing
> =>weight from the rotor, they can actually cause temperatures to
> =>increase a little.
> =>These holes create stress risers that allow the rotor to crack
> =>sooner, and make a
> =>mess of brake pads - sort of like a cheese grater rubbing against
> =>them at every
> =>stop.  Need more evidence?  Look at NASCAR or F1.  You would think
> =>that if drilling
> =>holes in the rotor was the hot ticket, these teams would be doing it.
> =>
> =>Ok, let's debunk the bigger rotors = better here also (again).
> =>
> =>Bigger rotors will make your friends think you are cool, bigger
> =>rotors look sexy, but
> =>bigger rotors do not stop the car.  What a bigger rotor will do is
> =>lower the overall
> =>operating temperature of the brakes - which is a GREAT idea IF your
> =>temperatures
> =>are causing problems with other parts of the braking system. (It can
> =>also changes how
> =>the brakes are modulated by the operator, which might be better
> =>for them).  The
> =>quick motto is bigger is better until your temperatures are under
> =>control.  AFter that
> =>point, you are doing more harm than good due to the load of steel
> =>hanging on the
> =>wheel that needs to accelerate each time the gas pedal is pushed.
> =>
> =>Finally, SS brake lines only remove compliance from the braking
> =>system, which really
> =>affects only the pressures and forces applied, not so much how cool
> =>the rotor is
> =>running...
> =>
> =>Again, this is an excerpt from a rather extensive braking article
> =>from Grassroots Motorsports,
> =>written by an anti-lock braking systems engineer with the Robert
> =>Bosch Corporation who
> =>is a Saturn racer for scR motorsports.
> =>
> =>In my opinion, this probably doesn't matter to the most of us
> =>anyway...very few of us
> =>are pushing are cars hard enough to get into the perfomance areas
> =>where these kinds
> =>of details actually make a difference very often.
> =>
> =>==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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