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      08-20-2008, 08:44 PM   #155
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Quote:
Originally Posted by lucid View Post
I wasn't suggesting they change the final drive. Why can't they change some of the intermediate ratios? Why can't the 5th gear ratio be changed as there is nothing specific about the 1:1 ratio I am aware of that requires it to be fixed? Is this about shaft spacing?
I believe 5th is a direct drive, meaning power is transmitted down the main shaft without torque being transferred to another shaft.
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      08-20-2008, 08:49 PM   #156
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Quote:
Originally Posted by Radiation Joe View Post
I believe 5th is a direct drive, meaning power is transmitted down the main shaft without torque being transferred to another shaft.
OK, I see, that would be slightly more efficient, lighter, and eliminate bending moments. Anyway, they could have still made 3rd and 4th slightly shorter though. Also, looking at gear ratios on sports cars, there are tranmissions out there that don't use direct drive such as the Gallordo and the F430.
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      08-20-2008, 09:27 PM   #157
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Quote:
Originally Posted by earlyapex View Post
Art,

This is an argument over a fairly subtle point. I'm just pointing out the fact that fixed calipers (which require multiple pistons, duh!) are marginally better at the edge. The real argument over brakes should work, roughly in descending order more or less, like this:
1) tires
2) weight
3) pad temp resistance
4 - tied) weight distribution
4 - tied) brake mass for heat absorption and fade resistance
6) brake design (caliper stiffness, pistons, etc.)

We are spending all out time at the bottom of the list. My point is that a fixed caliper is less flexible and easier to modulate. You think that isn't important because the M3 performed so well in some Car and Driver test from 100 to zero (which doesn't come close to replicating track braking).

I say it is important based on 10 years of experience with multiple different cars in actual club racing at many different tracks, but it's still a subtlety like changing from 1/16 to 1/32 of overall toe-out. Can I feel the difference? Yes. Could 99% of the population without experience at 10/10ths in racing? No way because they are going to miss the braking pionts by dozens of feet anyway.

Is it going to make a big difference in overall objective performance? No

Do more pistons sound good to balding stockbrokers? Absolutely, but so does a multi-cam high-revving V8...

Ok, I'm going to be a bit of a smart*ss here, so just try to laugh along.

I guess Porsche, ferrari, viper, z06, gtr, lotus, aston martin, Sti, Evo, lamborghini, audi, etc. (basically EVERY SINGLE performance car manufacturer in the world other than BMW) should fire all their blithering idiot engineers for using those stupid fixed calipers and hire the geniuses at BMW (who are in the process of converting to fixed calipers thermselves starting with Brembos on the 1 series, so they better hire them quickly as they are fast becoming fellow idiots).

If BMW engineers are so concerned with making sure they don't over-engineer things, why did they use a ridiculously complicated and expensive high-rev V-8, when the REGULAR (not Z06) chevy corvette engine has more horsepower and significantly more torque while using signficantly less fuel?

The point is that all these guys have to factor in marketing (sounds good but doesn't make that much difference - ie big red brembos), actual performance (more horsepower/more expensive and stickier tires) and economics (those stickier tires don't last as long, those multi-piston fixed calipers won't make a hoot of difference for 99.9% of drivers).

Are fixed calipers better? Yes. Are they "better enough" to justify the economics? Probably not, but then neither is that fancy V8.

OK, here I have to flat disagree completely. That's not even close to accurate (and may explain why you are ignoring the subtleties which become more important the faster you go). The M3 will exceed 130 on most tracks and 135 on many. The reduction in kinetic energy from 135 to 50mph (like Turn10a at Road Atlanta) is 163% more than 110 to 50. (which, admittedly, has nothing to do with caliper stiffness (or pistons for that matter)).

But it's harder to hit the braking points perfectly and maximize braking at 135 than 110. The harder it is to do, the more accurate you want the system to be.

You are also ignoring the fact that most track sessions are at least 30 minutes. Using your math, that's 90 back to back maximum braking efforts. The brakes aren't going to come close to cooling completely in the 20 seconds in between, and as they get hotter and hotter, the subtleties matter more and more.

Actually (as you are pointing out), tire friction and weight are far more important than pistons and calipers . See list at start of post.

Is driver skill more important than system ability? absolutely.

But the more skill you have, the more you are going to recognize, appreciate and utilize the subtleties of things like a finely tuned alignment and more sublte brake modulation.

For the masses, yes. But for those that can appreciate the subtleties? Well, that's theoretically why you would buy a BMW or porsche, right? They've got to design the car for those that can tell the difference because that translates to all the people who can't through word of mouth, magazine articles, internet forums, etc.

I've just ordered some pagids and am taking the 3000 mile M3 to sebring on October 5th, so I'll have an actual anecdotal report on real brake experience with good pads.
most people buy ANY car (thing) for ego, name recognition, appearance, etc.

the very same reasons you noted for the brembo brakes...

I bet 99% never drive at 9/10th's...we THINK we do, but someone like Hans Stuck would show us the folly of our logic

M3 Reno_Fernley 111
EVO track 109

I've yet to see a track test >115, let alone 140!

the big brake craze is like chia pets...why? because people will buy them...there is no tangible benefit, these are street cars...the floating caliper is better for street cars...BMW knows this...they used fixed calipers before they were 'vogue'...the actual cost difference? negligable...a couple of $ per caliper, when 1000's are being made...and I'm not sure to which advantage...

the Bosch handbook clearly states that foating calipers are better (and gives the reasons), and modern design has mitigated any inherent disadvantage...

if it was all about performance, why paint the calipers? it only traps heat and drives it into the piston and fluid...it produces an R value...F1 cars aren't painted, they are 'raw', in addition they are not machined smooth...

an irregular surface has more surface area, hence better radiation...

the ONLY benefit for painted, ancy calipers is marketing...most BMW owners transcend that level of (un)sophistication
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      08-20-2008, 09:47 PM   #158
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Quote:
Originally Posted by swamp2 View Post
Disagree.

On point 1 he asked about work performed by the brakes. The total work performed by the brakes would be larger for a stop from any given speed. Kinetic energy and potential energy both must be converted to heat by the brakes. I agree that lower friction will affect braking distance and that will be a small effect for most normal road grades.

On point 2 braking performance would suffer. Maybe not by a lot but the brakes must convert all of a vehicles kinetic energy to heat. "Converting" non rotating mass to rotating mass increases the systems total kinetic energy (translational + rotational) for a given tranlational speed. More energy is always negative for brake performance. This would be mitigated by the much larger thermal mass of the rotors which might even reduce braking temperatures.
look at it this way:
60-0 downhill or flat, kinetic, 1/2 (88)^2 ~ 3872 (ignore m, it's constant)
potential g delta h, assume a stopping distance of 112 ft at 10% grade (pretty steep)
U ~ 11 x 32 or 353
total energy ~ 353 + 3872 ~4225...so the added energy is only 8.4% of the total...
as I said, it would make negligable difference...
increasing the speed < 5% would be about the same effect...

as far as mass of the disc increasing vs distance/work, the only additonal energy would be that stored by the flywheel effect due to gravity (inertia)
W = distance x F, F = braking force which is the same, so any difference (if any) would be negligable...

distance = W/F since force is constant, and the work is only marginally increase, the distance is not greatly increased...
straight out of the Bosch book page 616

I also noticed they list all required DOT and TUV brake tests for certification...not one requires incline testing...
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      08-20-2008, 10:02 PM   #159
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Quote:
Originally Posted by ArtPE View Post
most people buy ANY car (thing) for ego, name recognition, appearance, etc.

the very same reasons you noted for the brembo brakes...

I bet 99% never drive at 9/10th's...we THINK we do, but someone like Hans Stuck would show us the folly of our logic
Speak for yourself if you like. You don't have to be as fast as Hans Stuck to drive a car at 9/10ths and be faster than 99% of drivers. Actually, the difference between the skill level of the average internet bench race junkie and an amateur race driver is far greater than the delta between that amateur driver and Stuck. Law of decreasing marginal returns wins here easily. And there's an easy objective test, lap times.

Quote:
Originally Posted by ArtPE View Post
I've yet to see a track test >115, let alone 140!
I'm not sure what info you are talking about or where this is coming from. the M3 will exceed 130mph on the straights of 90% of the decent sized tracks in the US. Heck, my old S2000 would hit 120 at sebring, road atlanta, etc. Have you ever driven on a real roadcourse? I'm not trying to pick at you, I'm just curious.

Quote:
Originally Posted by ArtPE View Post
the big brake craze is like chia pets...why? because people will buy them...there is no tangible benefit, these are street cars...the floating caliper is better for street cars...BMW knows this...they used fixed calipers before they were 'vogue'...the actual cost difference? negligable...a couple of $ per caliper, when 1000's are being made...and I'm not sure to which advantage...
That's a bit of an overstatement, but I agree with the basic point. For the most part it's overkill, but so is a tricked out high rpm quad cam engine when you can accomplish the same thing with a big fat chevy smallblock dating, more or less, to the 1950s.

I agree floating calipers are better for dealing with the vagaries of real life like pad material, warped rotors, water, etc., but that isn't as important when you replace your rotors for every track weekend.

Quote:
Originally Posted by ArtPE View Post
if it was all about performance, why paint the calipers? it only traps heat and drives it into the piston and fluid...it produces an R value...F1 cars aren't painted, they are 'raw', in addition they are not machined smooth...

an irregular surface has more surface area, hence better radiation...

the ONLY benefit for painted, ancy calipers is marketing...most BMW owners transcend that level of (un)sophistication
I agree completely. Hence my silly references to stockbrokers. BMW owners succumb to the ego just as much as anyone else (whether wanting the latest cool toy, or insisting on winning every internet argument over the tri-forum area...)
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      08-20-2008, 10:43 PM   #160
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I insist that this thread should be in the Track/AutoX forum.

My S2000 (I had two of them) would reach 120 mph at Pocono North with just 240 Hp (stock car). My 380 Hp GT3 at Cali Speedway (ROVAL) ran 151 mph (Traqmate data verified), and 147 mph at Pocono North, and 153 mph at Watkins Glen, and 140+ mph at Lime Rock.

Look on the chart below the top speed achieved by the wrong geared M3 with manual transmission:

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      08-20-2008, 11:25 PM   #161
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That is a great article, its sitting in my room right now. As much as I believe that there are plenty of tracks where the M3 will be hitting 130, which it certainly does at willow springs. They did have pro's driving these cars at the tracks and I think the one with the M3 hitting 148 is an oval with major banking. Not that I wouldn't track my car there, but I think banked ovals are in the minority for track days. On the flipside, the lower Vmax scores are from a coned auto-x event. Auto-x events are notorious for being extremely tight courses and having low speeds, due to area confinements. I still think that the majority of road courses would let a 400hp car hit well over 100mph.
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      08-21-2008, 01:36 AM   #162
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Quote:
Originally Posted by ArtPE View Post
look at it this way:
60-0 downhill or flat, kinetic, 1/2 (88)^2 ~ 3872 (ignore m, it's constant)
potential g delta h, assume a stopping distance of 112 ft at 10% grade (pretty steep)
U ~ 11 x 32 or 353
total energy ~ 353 + 3872 ~4225...so the added energy is only 8.4% of the total...
as I said, it would make negligable difference...
increasing the speed < 5% would be about the same effect...
I was not refering to a specific case. He asked if the work would be greater and it would. We agree the IRL differences on any real hill would be small.

Quote:
Originally Posted by ArtPE View Post
as far as mass of the disc increasing vs distance/work, the only additonal energy would be that stored by the flywheel effect due to gravity (inertia)
W = distance x F, F = braking force which is the same, so any difference (if any) would be negligable...

distance = W/F since force is constant, and the work is only marginally increase, the distance is not greatly increased...
straight out of the Bosch book page 616
Same point here, a small but real effect. "Magically" move non rotating mass to rotating mass and at the same translational speed you have more energy, period, no argument possible. The same effect is why heavier wheels have a small but measurable impact on vehicle performance, acceleration and braking.
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      08-21-2008, 03:58 PM   #163
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I'm no expert or professional driver:
I have 1 mil miles in BMW/Porsches, 500k in M3's alone
my first Porsche was in 1977, first BMW in 1981...
at least 40+ driving schools, several DoD, etc.
I used to race (club) 911's and 2002's...snow, ice, dirt/gravel, tarmac
I have at least 200k 'just for shytes & giggles' miles...back roads, etc.
I'm a novice...I admit it...it keeps me from doing stupid things

I would not be faster with Brembos vs oem on any M3...especially on the street...
you want a track car? get a 944 or 325 and strip it down/build it up...
but for most classes, stock brakes are required...iirc, sliding/1 piston on both

as far as cost being the reason BMW made their choice:
anybody know the following pricing?
e92 M3 front caliper/carrier/rotor (it's >$900 for the e46 M3 ZCP per side!)
e87 135i front caliper/rotor
just curious...
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      08-21-2008, 04:03 PM   #164
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Quote:
Originally Posted by ArtPE View Post
as far as cost being the reason BMW made their choice:
anybody know the following pricing?
e92 M3 front caliper/carrier/rotor
e87 135i front caliper/rotor
just curious...
I don't know the answers to your question, but during a local BMW event, when Larry Koch was asked why they went for the current caliper design on the M3, he mentioned that it allows for rotor expansion, and then pointed out that it also costs less with a smile.
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      08-21-2008, 04:08 PM   #165
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Quote:
Originally Posted by lucid View Post
I don't know the answers to your question, but during a local BMW event, when Larry Koch was asked why they went for the current floating design on the M3, he mentioned that it allows for rotor expansion, and then pointed out that it also costs less with a smile.
the rotor allows for expansion (radially) and run-out varience also...
but my guess, it's ~ the same cost as any rotor...
it's aluminum, iron, x-drilled and floating on cast in place pins...big too
the only thing it lacks, it's not rebuildable...

it's the calipers I'm curious about
they cost $540 per side on the ZCP...I bet the 135i's don't cost any more...
I bet the e9x M3's are at least $650
or they would not have used them on a lower target price car
unless they are trying to appeal to a certain demographics 'taste'
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      08-21-2008, 04:47 PM   #166
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now here's some BMW brakes...lol http://www.itv-f1.com/News_Article.aspx?id=43660

seriously though, capture the kinetic energy for reuse...
infinite modulation, absolutely control...much easier to control an electric signal than a mechanical/hydraulic circuit...
ecu could control the throttle/brake in synch...driver steers and uses one pedal, the throttle

no heat generated, or at least much less...
I wonder what it looks like?
a motor/generator on the axle? or
or a rotor disc (like the brake disc) spinning thru a stator toroid/magnet...
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      08-21-2008, 05:20 PM   #167
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Quote:
Originally Posted by ArtPE View Post
the rotor allows for expansion (radially) and run-out varience also...
but my guess, it's ~ the same cost as any rotor...
it's aluminum, iron, x-drilled and floating on cast in place pins...big too
the only thing it lacks, it's not rebuildable...

it's the calipers I'm curious about
they cost $540 per side on the ZCP...I bet the 135i's don't cost any more...
I bet the e9x M3's are at least $650
or they would not have used them on a lower target price car
unless they are trying to appeal to a certain demographics 'taste'
I believe he was referencing the cost of the entire brake system, current M3 design vs. a multi-piston fixed caliper alternative design.

The following page might give you a sense of the retail prices of the caliper assembly in Europe:

http://bmwfans.info/original/E92/Cou...4/ill-34_1618/

The same site should have retail pricing info on other BMW models as well.
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      08-21-2008, 06:03 PM   #168
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Quote:
Originally Posted by lucid View Post
I believe he was referencing the cost of the entire brake system, current M3 design vs. a multi-piston fixed caliper alternative design.

The following page might give you a sense of the retail prices of the caliper assembly in Europe:

http://bmwfans.info/original/E92/Cou...4/ill-34_1618/

The same site should have retail pricing info on other BMW models as well.
thnx, I checked there, for some reason they omitted the prices for the 2 items...

they don't have the 135i listed yet...
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      08-21-2008, 08:52 PM   #169
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Quote:
Originally Posted by ArtPE View Post
I would not be faster with Brembos vs oem on any M3...especially on the street...
...sure, but that's not the point of the post...re-check the title. OK, we hear you...Brembos are no better on the street, just like Bosch's book says...

Quote:
Originally Posted by ArtPE View Post
you want a track car? ...
No, I want my high performance ///M car to be able to do the same thing my $30K subaru can do... run a large selection of pads, that can be changed easily, and not taper them so they wind up costing twice as much in the long run.

When the calipers start spreading, and pads are lasting half as long as they should, we'll hear from the track people who will move to fixed calipers/multi-piston set-ups. I only hope, financially, that I'm not one of them...
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      08-21-2008, 08:56 PM   #170
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Quote:
Originally Posted by ace996 View Post
...sure, but that's not the point of the post...re-check the title. OK, we hear you...Brembos are no better on the street, just like Bosch's book says...


No, I want my high performance ///M car to be able to do the same thing my $30K subaru can do... run a large selection of pads, that can be changed easily, and not taper them so they wind up costing twice as much in the long run.

When the calipers start spreading, and pads are lasting half as long as they should, we'll hear from the track people who will move to fixed calipers/multi-piston set-ups. I only hope, financially, that I'm not one of them...
they would not be faster on the track...

and there is a healthy selection of pads for the e46, there will be for the e92 in due time
it takes 5 minutes to change pads...per side...
but better change rotors too, cause they're gonna suck on the street after being thrashed
the pads do not taper, it's one advantage of the system...
solid bushings will reduce it even more
'track people'
<1% of the cars total mileage...get a track car...you can get one for less than a set of brembos, track wheels/tires...
you guys make 60k sound like a lot of money...

wtf?
"Arcadian, I've fought countless times, yet I've never met an adversary who could offer me what we Spartans call "A Beautiful Death." I can only hope, with all the world's warriors gathered against us, there might be one down there who's up to the task."
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      08-21-2008, 10:04 PM   #171
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there are so many variables in the brake system performance equation, that looking at calipers is moot: my order

tires
driver
pad compound
pedal/master cylinder/system hydraulic balance control systems, abs, etc.
rotor diameter
calipers

rotor dia is critical...look at an M3 vs a 997...huge difference
why so important?
brake torque is the stopping force, T = r F
r = rotor radius, F = brake force or hydraulic pressure x piston area = pad area x piston pressure
now if r is bigger, F is smaller for a given T...still with me?

now friction = Ff = u F...see, if F is smaller, so is friction force for the same stopping power (brake torque)...if friction force is smaller, so is the heat density...
and it makes sense, the path/area around the rotor is larger...

it makes no sense to look at 1 component in a complex system...
there's a quote floating around by the chief engineer on the GT-R project...that calipers are moot, it's rotor diameter that makes the difference...and they are huge on the GT-R, 4 x 15"
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      08-22-2008, 10:17 AM   #172
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Quote:
Originally Posted by lucid View Post
Although I agree with some of your points, the above point is unsubstantiated. We discussed that at some length, and there is no evidence to support it that I am aware of. Take the engines out and strap them onto a testbed. Run them steady at say, 100hp, 200hp, 300hp, 400hp, outputs and measure consumption. Then we have some data to evaluate the claim. One can argue that high revs can results in higher fuel consumption, but compression ratio is the major factor in efficiency. 10.7 vs 12.0. Obviously, there are other factors as well. Comparing efficiency numbers of the entire package is a different story (there is a 500lb weight difference to begin with).
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.

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      08-22-2008, 11:39 AM   #173
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Quote:
Originally Posted by ArtPE View Post
the pads do not taper, it's one advantage of the system...
http://www.bimmerfest.com/forums/sho...7&postcount=16

Link above shows pretty bad taper and some bushings that are supposed to help this non-existant taper

Quote:
Originally Posted by ArtPE View Post
solid bushings will reduce it even more
Reduce what?...you just said there is no taper.

So what is it? Is there taper, like evey other slider experiences when used hard on a track or is there no taper and those solid bushings are just BS?


Quote:
Originally Posted by ArtPE View Post

rotor dia is critical...look at an M3 vs a 997...huge difference


it makes no sense to look at 1 component in a complex system...
there's a quote floating around by the chief engineer on the GT-R project...that calipers are moot, it's rotor diameter that makes the difference...
And what about pad size? The multi-piston calipers use pads that are larger..in contact patch...they're able to take more heat and will last longer..as they do in every other application.


Quote:
Originally Posted by ArtPE View Post

wtf?
"Arcadian, I've fought countless times, yet I've never met an adversary who could offer me what we Spartans call "A Beautiful Death." I can only hope, with all the world's warriors gathered against us, there might be one down there who's up to the task."
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???...WTF???? Your question?
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Last edited by ace996; 08-22-2008 at 11:56 AM.
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      08-22-2008, 12:38 PM   #174
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Quote:
Originally Posted by ace996 View Post
http://www.bimmerfest.com/forums/sho...7&postcount=16
Link above shows pretty bad taper and some bushings that are supposed to help this non-existant taper

Reduce what?...you just said there is no taper.

So what is it? Is there taper, like evey other slider experiences when used hard on a track or is there no taper and those solid bushings are just BS?

And what about pad size? The multi-piston calipers use pads that are larger..in contact patch...they're able to take more heat and will last longer..as they do in every other application.


???...WTF???? Your question?
all pads taper to a degree...but it's not a problem...it's normal...
they have to...the disc is rotating in one direction primarily...

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...

Q = -kA(dT/dx)

take a look at the relative difference of the pads areas...
as you can see heat conduction is linear with the area, NOT squared...
so a small difference in area means nothing if the material is suitable...

this is all about bling...otherwise they would not epoxy coat the calipers...
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      08-22-2008, 03:36 PM   #175
earlyapex
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Quote:
Originally Posted by ArtPE View Post
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...
Art,

I actually don't think we disagree all that much about most of this stuff as, again, we are talking minor differences.

But this statement is just funny. I don't know where you get some of these crazy ideas to prove your points.

I've seen pads get so hot that they change color and literally cook the rubber seals around the pistons.

You ever change pads in the middle of an endurance race? You have to wear oven mits as they are literally hundreds of degrees.
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      08-22-2008, 04:36 PM   #176
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Quote:
Originally Posted by earlyapex View Post
Art,

I actually don't think we disagree all that much about most of this stuff as, again, we are talking minor differences.

But this statement is just funny. I don't know where you get some of these crazy ideas to prove your points.

I've seen pads get so hot that they change color and literally cook the rubber seals around the pistons.

You ever change pads in the middle of an endurance race? You have to wear oven mits as they are literally hundreds of degrees.
http://soundamerica.com/sounds/movies/D-i/Goodfellas/ funny.wav
a nickle jammed under a train wheel will prevent it from moving
as you know, trains are electric...the diesel drives a genset, and there is an electric motor in each 'truck'...a gear tranny could not stand up to starting a train...

but the torque curve of the motor is so smooth it could not 'lift' the ~200 tons the height of a nickle

I think in strange ways...I was born an engineer who happened to get an education...not a normal person who chose to be an engineer

oh, I'm sure the pads are very hot...but the rotors glow cherry red...

I've only had 1 pad failure in all my miles, on my e36 the front right material cracked and seperated from the backing...the pads were new and not really being thrashed...they were PF metal masters iirc
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