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cross drilled rotors Scott Williams is WRONG!



>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.

Uh, no...I was just asking you to clarify your question / statement if you read
what I was writing further down.  I was trying to guess what your point was.  I
was not talking about the size of the disc below, only the caliper 
piston diameter
and I was trying to understand what your statement was.  So I am really not
sure what you're disagreeing with...however, I am happy that this has given
you an opportunity to explain this deeper.

>
>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.

I think this is part of exactly what I was trying to educate everyone about,
the article I posted discusses this.

>
>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.

The article I posted also mentions this exact thing too, so I am aware.

>
>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.

In fact, this is just about the point I was asking you to clarify, 
and I was not
disagreeing.  Go read it again if you'd like.

>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.

Yes, this was also discussed in the article I posted, and I was aware of the
differences.

One statement I made below was critically incorrect though and I mistyped
something (It was getting late, forgive me).  Increasing the piston caliper
diameter can increase the clamp load for a given input volume...but as I've
been saying all along, it doesn't necessarily increase stopping power.


==Brett

>
>
>
>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