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      08-22-2008, 08:00 PM   #177
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Quote:
Originally Posted by bruce.augenstein@comcast. View Post
You're speaking of bsfc numbers here, which in my opinion would be interesting to know, but are not germain to the discussion. The Chevy would be optimized with much longer gearing (because of its massive torque advantage and lower rpm limit), and would thus provide better mileage. The "proof" point is the GTO, which makes better mileage even with increased weight.

Bruce
The focus of the discussion was clearly the engine, and not the entire package as I mentioned in my post. Gearing obviously factors in if you want to consider the entire "package" and driving conditions. But if your point is that the corvette has more available torque down low (speaking of differences in the relative shapes of the torque curves), and hence is more drivable in high gears at low rpms even with the longer gearing than the M3 for that reason, that would be interesting to study by looking at torque at the wheels for a hypothetical M3 with slightly longer gearing in the higher gears. From the perspective I took, I don't know that the GTO is more efficient than the M3 if they were being driven equally hard (with similar power demands which should negate the gearing effects). We have one previous GTO owner on the forum which provided supporting, yet anecdotal, evidence in that regard.
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      08-22-2008, 11:11 PM   #178
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Quote:
Originally Posted by ArtPE View Post
although the area is larger, that means little
especially if the mean radius of the centroid of their area is smaller...
Ff = u N
you see area in that equation?

what this means for a constant rate of decleration (brake torque)
the pressure on the rotor is the same (all else being constant)
it's the material that matters, not the area...
a larger pad may wear less, but not stop better or heat less...
what is more important is the size (mass and surface area) of the disc
most of the heat goes into the disc, NOT the pads...it's ENGINEERED that way...you could stop a train with a large enough disc and a properly designed 1 sq in pad and touch the pad when done, it would only be warm...
You do realize that this equation for friction is APPROXIMATE, right? In many cases it holds very accurately, in some decently and in many others not at all. Improvements can come from allowing u to be a function of speed, temperature, area or pressure.

Your train brake statement is very likely false. At least in terms of stopping from any typical realistic combination of speed/load/rate/pad material. The pressure required would be so large it would heat the pad so greatly that F=mxFn would not hold the pad material would melt/sluff/destroy itself.
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      08-23-2008, 08:08 AM   #179
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Originally Posted by ArtPE View Post
...most BMW owners transcend that level of (un)sophistication

"most".
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      08-23-2008, 08:17 AM   #180
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Originally Posted by Radiation Joe View Post
"most".
but not 'all'
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      08-23-2008, 05:51 PM   #181
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You want to see area? this is what area looks like

You want to see area? this is what area looks like

This what a brake is supposed to look like Luckily for you stupid guys like ART
in 09 BMW will come out with Brembos.
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      08-23-2008, 06:10 PM   #182
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Quote:
Originally Posted by swamp2 View Post
You do realize that this equation for friction is APPROXIMATE, right? In many cases it holds very accurately, in some decently and in many others not at all. Improvements can come from allowing u to be a function of speed, temperature, area or pressure.

Your train brake statement is very likely false. At least in terms of stopping from any typical realistic combination of speed/load/rate/pad material. The pressure required would be so large it would heat the pad so greatly that F=mxFn would not hold the pad material would melt/sluff/destroy itself.

just like F = ma is an 'approximation'...it's all a matter of degree...
u is a constant of the material(s), and may or may not be linear...

ever see the brake on an elevator? very small...very small...but the drum is very large...it's a reverse drum type, 1 shoe...

the pressure would be very small if the radius were very large...
lets say the pad is 1 in^2 ...makes the math easy...
say it takes 10,000 lb-ft of stopping torque (T = r F)...to stop the load...
at 100' radius it needs 100 lbs of force F...so psi = 100, not much...
at 10' it needs 1000 lbs of force or 1000 psi...much more
so at 1000' raduis, it would need only 10 lf F or 10 psi
and so on, big enough and the pad would barely touch the disc...
and since Ff ~ u F, since F is small, so is friction force...

same stopping power, different pressure, hence much different friction force and heat generated...
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      08-23-2008, 06:13 PM   #183
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Quote:
Originally Posted by DavidAMG View Post
You want to see area? this is what area looks like

This what a brake is supposed to look like Luckily for you stupid guys like ART
in 09 BMW will come out with Brembos.
the 09 M3's don't have brembos...so who's stoopid?

and with a idgit like you calling me stupid, it doesn't carry much weight...
but I'm sure you are well aquainted with limited intellectual prowess...
breathing for you is not an autoreflex, and I'm sure you do it with your mouth open, and some spittle on your lip

you do realize the M3 brakes are bigger than the C63? a car that weighs >400 lbs more?
F 14.2 vs 14.2
R 13.8 vs 13.0
a true genius

maybe you should leave this discussion up to the big boys...
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      08-23-2008, 06:20 PM   #184
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I remember reading an article of a braking system which replaced the calipers and pads with magnets. The advantages are clear to be seen, no wear or fade but that was over 5 years ago and nothing has been heard since. Another systems which used two disc instead of the normal one, both smaller with double the calipers and pads, this too seems to have fallen by the way side.

It's amazing with all the advances being made else where that brake technology hasn't made the same jumps.
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      08-23-2008, 06:21 PM   #185
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Quote:
Originally Posted by ArtPE View Post
just like F = ma is an 'approximation'...it's all a matter of degrees...
u is a constant of the material, and may or may not be linear...
F=ma is much deeper than it appears. The way to properly interpret F=ma is really to say the the motion of an enormous variety of real world bodies and mechanical systems is goverened by a 2nd order partial differential equation where the forces can be descibed by functions of speed and postion. This is not an approximation, it is exact (within the bounds that these bodies speeds may be considered negligible compared to the speed of light!).

Ff=u Fn is an enormous approximation compared to F=ma.
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      08-23-2008, 06:23 PM   #186
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Quote:
Originally Posted by ArtPE View Post
you do realize the M3 brakes are bigger than the C63? a car that weighs >400 lbs more?
F 14.2 vs 14.2
R 13.8 vs 13.0
a true genius

maybe you should leave this discussion up to the big boys...
And look at those "beautiful" "high tech" fixed single material rotors as well . Bling bling for the AMG...
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      08-23-2008, 06:29 PM   #187
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Quote:
Originally Posted by swamp2 View Post
F=ma is much deeper than it appears. The way to properly interpret F=ma is really to say the the motion of an enormous variety of real world bodies and mechanical systems is goverened by a 2nd order partial differential equation where the forces can be descibed by functions of speed and postion. This is not an approximation, it is exact (within the bounds that these bodies speeds may be considered negligible compared to the speed of light!).

Ff=u Fn is an enormous approximation compared to F=ma.
iirc it's not a partial differential equation...it's only differentiated with respect to time...although it can be written as a 2nd order linear system...

s = 1/2at^2 (assuming initial v and s of 0)
ds/dt = v = at
d2s/dt2 = dv/dt = a

s = 1/2 d2s/dt2 t^2 + ds/dt t + s0

having said that, both ma and uN give the same order of approximation, assuming m, a, u and N are measured to the same degree...and over an appropriate range of observation
in fact friction is generally MORE linear than acceleration

edit: after thinking about it if the coordinates were (x,y,z,t) I guess you could look at it with respect to each dimension, so partial diffs would apply...but that's what vectors are for
I was referencing simple linear motion in one plane...

Last edited by ArtPE; 08-23-2008 at 07:33 PM.
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      08-23-2008, 06:33 PM   #188
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Quote:
Originally Posted by swamp2 View Post
And look at those "beautiful" "high tech" fixed single material rotors as well . Bling bling for the AMG...

the AMG rotors are not floating or 2 piece? I did not know that...
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      08-23-2008, 06:37 PM   #189
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Quote:
Originally Posted by DavidAMG View Post
You want to see area? this is what area looks like

This what a brake is supposed to look like Luckily for you stupid guys like ART
in 09 BMW will come out with Brembos.
Thank you for registering just to make this valuable contribution. You sure taught us all something.
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      08-24-2008, 01:13 AM   #190
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hey!... back to the original question - which I am still not sure what it is means!

"M owners Brakes How do you like them Track? "
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      08-24-2008, 02:27 AM   #191
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Quote:
Originally Posted by ArtPE View Post
the AMG rotors are not floating or 2 piece?
Some AMG cars may have floaters but those on the C63 sure are not. They are 1 piece cast iron. Hey at least they are cross drilled.

On friction vs. Newton, I'll vehemently disagree. Yes many system can be written as ordinary 2nd order differential equations. However sometimes when you write equations for classical systems, equivalent to constructing them by F=ma, using variational principles in the form of Largange's or Hamilton's equations you definitely get PDEs. Whether or not friction is linear (which even considering the simple and common effect that starting friction is usually greater than sliding friction -> NON LINEAR) the ability of Newtons law to very accurately describe an enormous range of phenomena is truly amazing. Ff = uFn is very often a rough approximation. Comparing the two is like comparing apples and organges in terms of their power, accuracy, importance, universality, etc.

We digress... but indeed entertaining. Cheers.
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      08-24-2008, 11:16 PM   #192
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      08-25-2008, 04:14 AM   #193
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LOL. BTW OP bought a c63.
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      08-25-2008, 05:09 AM   #194
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This debate has been going on for 9 pages now, whether floating or fixed is better, 1 piston or multi-piston.

Can we agree on one thing, all racing cars use multi-piston fixed calipers. So for racing at least the other route that is not used by BMW on the M3 is best, but not necessary for normal road/trackday use.
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      08-25-2008, 06:33 AM   #195
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Ok, I just got done with a 3 day driver's school at the brand new Thunderbolt Circuit at NJ Motorsports Park in southern NJ. The track has 5 braking zones on a 2.1 mile circuit. 2 of these braking zones include braking from 100+ mph to about 60ish including the turn 1 where I was getting to 135+ and had to brake to 65-70.

The brakes never faded at all the entire weekend. They were just as strong on the last lap as they were when I arrived at the track. Also, I was braking nearly as deep as some of the guys with aftermarket brakes which says a lot considering the weight of the E92. I was using stock pads and stock tires.

Bottom Line: The brakes are very effective on the track, there is truly no need to change them or upgrade to an aftermarket brake system for track use. The only reason to upgrade the brakes, is because they aren't all that nice to look at (calipers not rotors).
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      08-25-2008, 08:16 AM   #196
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Quote:
Originally Posted by skierman64 View Post

The brakes never faded at all the entire weekend. They were just as strong on the last lap as they were when I arrived at the track. Also, I was braking nearly as deep as some of the guys with aftermarket brakes which says a lot considering the weight of the E92. I was using stock pads and stock tires.

Bottom Line: The brakes are very effective on the track, there is truly no need to change them or upgrade to an aftermarket brake system for track use. The only reason to upgrade the brakes, is because they aren't all that nice to look at (calipers not rotors).
I have done 2 days now with basically the same result.The only upgrade that I plan to do is probally a more track oriented pad.The other thing is that the stock setup recovers quite well from the track abuse.When pushed on the track I have found that they do suffer a bit from soft pedal and shuddering but this goes away once they are cooled off.For what the car is, the brakes are very good.
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      08-25-2008, 12:16 PM   #197
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Quote:
Originally Posted by footie View Post
This debate has been going on for 9 pages now, whether floating or fixed is better, 1 piston or multi-piston.

Can we agree on one thing, all racing cars use multi-piston fixed calipers.
NO - we can not agree on that. there are many racing classes that use stock brakes.
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      08-25-2008, 12:31 PM   #198
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I ran my car for almost 2 hours in the canyons... up and down, up and down... and I was really running it at those canyons too to the point that I've seen the DSC light come on several times... and during that time, not a single shudder or change in the pedal feel... I was a little concerned with what I've read on the M3 brakes but after this little exercise, I think i'll be okay.... not to say that it can handle a full weekend of high speed tracking but that's to be expected Cheers.
Quote:
Originally Posted by Gearhead999s View Post
I have done 2 days now with basically the same result.The only upgrade that I plan to do is probally a more track oriented pad.The other thing is that the stock setup recovers quite well from the track abuse.When pushed on the track I have found that they do suffer a bit from soft pedal and shuddering but this goes away once they are cooled off.For what the car is, the brakes are very good.
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