cross drilled rotors Scott Williams is WRONG!

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

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

> >brett,
> >while the guy in the article is an expert  he had to simplify some stuff.
> >while going to bigger calipers MIGHT requrie more fluid to make them move.
> >they dont necc have to. For example IFyou could get the same volume
> >requirement  for two calipers  ie. the same force for the same amount of
> >psi as related to his article. getting a larger diameter system would be
> >worth it. assuming there wasnt a significant increase in mass.
>
> But if it resulted in the same clamping force, where is the win
> there?
brett are you gonna make me bust out my physics book? I will if required.
but try this.

given 3 discs of small, medium and large.
medium is typical installed size brakes 9.4 vented.
small is very small just larger than the actual hub.
and all three have identically sided brake pads. ie the contact area for
all of them are the same. and they all use the same caliper. so all of
them apply the same clamping force to the disc. The argument you are
presenting is that they all 3 would have exactly the same stopping power
for the vehicle. Is this correct?

If that is the idea you are presenting you are infact wrong. If not your
not making yourself clear.

If you were right ther would be no point in leverage. and using that big
ass pipe to lengthen the breaker bar for the front hub axle nuts would be
pointless. Torque works in both directions. acceleration and deceleration
which is just negative accleration.

Once again as an example if your case were true motorcycles would use the
smallest diameter disc possible. WHich is simply not the case. Most
performance bikes today use discs very near to the diamater of the front
wheel, and there are 2 discs. My old VFR750F uses a disc about 2/3 the
size of the wheel diameter, and they are 4 pistion calipers on each side
of the front wheel.

Next topic.
multiple piston calipers. yes these can and do save unsprung mass and
increase brakeing force for the same amount of incompressable fluid moved.
If you dont believe. take a trip down to ANY rice rocket shop, Honda,
suzuki, yahmaha, and even buell. why do they use smaller dual sided
calipers. Because a larger piston requires more fluid to move. and when
the master clyn is very limited to the force that can be applied and the
amount of fluid that can be moved optimization of the force applied is
required. remember there is only a 2-4" lever arm pushing down on that.
and my bike is quite heavy with me and a passenger on it. we push close to
800lbs. 450-500 for the bike + 350 for the passengers. The GVWR on our
cars is around 2800 lbs. but you have power assisted brakes with your leg
pushing on the brake pedal that is about 8-12" of a lever arm. So it
basically goes to show that the brakes in our cars are VERY inefficent.
And the ones on my bike are cross drilled and non-vented.



brian
2.0L Topless bunny 10.1 crossdrilled in the front and they are too much
for the current tires ast he front wheels slide to easily.
91 VFR750F with great big ass brakes that can outbrake 90+% of ALL cars on
the street. even those w/ ABS.


  I assume
> you are talking about the heat handling properties that could be present?
> I also believe you might have misspoke when you said larger diameter system,
> I assume you are referring to having a virtually larger diameter through
> multiple pistons?  Becuase, having a larger diameter of a piston given the
> same input volume results in lower pressures being generated.
>
> >ways that this can be accomplished.
> >using multiple small diameter plungers. a light weight (xdrilled) rotor.
> >so for most street applications the actual RIM that people use is going to
> >effect thier unsprung weight more than the rotor. ie for a 30% increase in
> >diameter and a 10% increase in weight.. its an acceptable tradeoff.
>
> Sure, the rim probably has more affect as far as weight goes here, but this
> discussion was primary aimed at braking systems, and getting after some
> of the incorrect assumptions that many people have on how to improve it. I
> totally understand that there are more forces at work here then what we've
> talked about, or what was outlined in that article...but there were many
> factors that were correct in that piece, which I do not think are
> well understood
> by everyone...including myself before I started doing some actual research.
>
> >esp if a light weight cooll looing rim is usea typical VW tear drop rim
> >but remember the suspension geometyr on our cars was designed for that
> >heavy ass wheel.
>
> Actually, it probably wasn't...remember, it was pretty much the same as
> far as basic geometry since 1974, when the cars were running fairly lightweight
> 13 inch steel or aluminum wheels.  Unless that's not what you were talking
> about, or bunch or words got chopped off by your connection... :-)
>
> >
> >and he is also coming from a road racer point of view. not a dail driver.
> >brian
>
> Which I think is even more important actually...road racing can amplify small
> problems in systems quite a bit.  That kind of driving can really find the
> weaknesses in systems, especially braking.  As I mentioned in one of my
> posts, most of the tweeking we do to our street driven cars braking systems
> don't really matter as we generally do not drive the cars hard enough for it
> to make a big difference.  It was just the misconception that many of us
> that doing certain things were actually going to _increase_ performance,
> which is what this has all been about.  That's not to say that changing or
> updating the brakes on our cars isn't a good thing, as modifying your system
> to tune it to how you like it, or freshening all the parts is obviously great.
>
> Tuning it to how you like it can include caliper piston diameters, master
> cylinder diameter, rotor dimensions, pad compounds, etc all factor into it.
> However, we probably shouldn't say that changing these items is
> a universal performance enhancement without understanding what variables
> it's affecting, or how the braking system actually works.
>
> ==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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