BMW M3 Forum (E90 E92)

BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read


Go Back   M3Post - BMW M3 Forum > E90/E92 M3 Technical Topics > Suspension | Brakes | Chassis
 
Post Reply
 
Thread Tools Search this Thread
      08-20-2008, 01:06 AM   #133
swamp2
Lieutenant General
 
swamp2's Avatar
 
Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

Posts: 10,140
iTrader: (1)

Quote:
Originally Posted by ArtPE View Post
1 not really...for a given speed it would be ~ the same...
but braking would take longer for the same pedal force because the tire is not perpendicular to the road...friction decreases...you would have a bit more to get rid of due to the elevation change (potential energy) Ep ~ m g delta h

2 not much...the cars mass would remain the same
distance would ~ the same...
although heat dissipation would improve due to larger thermal mass
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.
swamp2 is offline   United_States
0
Reply With Quote
      08-20-2008, 01:10 AM   #134
swamp2
Lieutenant General
 
swamp2's Avatar
 
Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

Posts: 10,140
iTrader: (1)

Quote:
Originally Posted by earlyapex View Post
One of the reasons for multi-piston calipers is feel, not braking distances recorded on milimeter accurate gps-accelerometers. You missed the point of my post.
Agree for sure about braking distance not being improved by multiple pistons. I am interested to hear more about these measurements. Slightly off topic but why use gps "acclerometers" to get (or try to get) mm accuracy? Wouldn't a traditional accel be better?
swamp2 is offline   United_States
0
Reply With Quote
      08-20-2008, 01:37 AM   #135
TLud
Colonel
 
TLud's Avatar
 
Drives: '12 Golf R
Join Date: Jun 2008
Location: Texas

Posts: 2,280
iTrader: (3)

I'm not the genius that my old man with a PhD in physics is, so I'm sure he would and you will point out that everything I'm about to say is dead wrong, but here goes...

Quote:
Originally Posted by Irb Digital
1. Since gravity has a significant impact on V (uphill and downhill) and changes the amount of work needed from the brakes, a down hill braking section would require more work from the brakes, correct?
Quote:
Originally Posted by ArtPE
1. not really...for a given speed it would be ~ the same...
but braking would take longer for the same pedal force because the tire is not perpendicular to the road...friction decreases...you would have a bit more to get rid of due to the elevation change (potential energy) Ep ~ m g delta h
Quote:
Originally Posted by Irb Digital
1. In regards to your answer to my first question. IMHO the tire is still perpendicular to the road, the vehicle's center of gravity is what changes. If a vehicle is braking on a downhill more weight would be sitting on the front tires. Wouldn't this increase friction as well as contact patch? You answered not really but looking at the last sentence it seems that there is a direct relation between (E ~ pE) and the elevation change, due to gravity.
Art, not to nitpick, but I think you somewhat confused Irb with the bolded language. The tire remains perpendicular to the road at all times unless the car leaves the ground. The more correct way of stating it would be to say that the force of gravity on the tire is not normal (perpendicular) to the road.

Wouldn't the gravitational force be designated as mg * sin(a), where a is the gradient?

Also, on a downward slope, I don't understand how decreased friction caused by changing slope (as opposed to changing surface) is really different from what Irb meant by gravitational force having more of an effect on forward acceleration. Either way you look at it, the mg changes from pulling the car straight down to pulling the car forward, shifting the center of gravity more over the front wheels, decreasing the friction between the rear wheels and the ground, increasing the friction between the front wheels and the ground, and thereby (1) increasing the force necessary to stop the vehicle, and (2) increasing the work the front brakes must do to the extent the rear wheels are traction-limited. Of course, all of this assumes constant slope. Increasing or decreasing slope adds a slew of other factors.
TLud is offline   United_States
0
Reply With Quote
      08-20-2008, 07:27 AM   #136
earlyapex
Private
 
Drives: 2008 E90 M3
Join Date: Aug 2008
Location: Raleigh, NC

Posts: 81
iTrader: (0)

Quote:
Originally Posted by swamp2 View Post
Slightly off topic but why use gps "acclerometers" to get (or try to get) mm accuracy? Wouldn't a traditional accel be better?
I was just trying to be funny. Guess I missed.
earlyapex is offline   United_States
0
Reply With Quote
      08-20-2008, 07:31 AM   #137
Radiation Joe
Veni Vidi Vici
 
Radiation Joe's Avatar
 
Drives: '11 JB/BBe-6sp-e90
Join Date: Jul 2008
Location: Macungie PA

Posts: 2,749
iTrader: (0)

Garage List
2011 e90 M3-Sold  [4.25]
2003 RS6 - Sold  [0.00]
2009 e90 M3 - Gone  [0.00]
2003 M3 SOLD  [0.00]
old 2002  [5.00]
130+ at Watkins Glen on street tires
140+ at Road America on street tires
120+ at Laguna Seca
130+ at Thunderhill

150+ at Brainerd in the RS6 with those 8 piston Brembos that were good for about 4 laps.
__________________

Dinan compliment of stuff plus PF rotors and RG63s. Enough for now.
Why, yes. I am an abrasive bastard.
Radiation Joe is offline   United_States
0
Reply With Quote
      08-20-2008, 08:26 AM   #138
earlyapex
Private
 
Drives: 2008 E90 M3
Join Date: Aug 2008
Location: Raleigh, NC

Posts: 81
iTrader: (0)

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...


Quote:
Originally Posted by ArtPE View Post

any of us trying to out smart 20 PhD's at BMW (actually Conti/Teves) is laughable...
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.


Quote:
Originally Posted by ArtPE View Post


the M3 will never exceed 110 on most tracks...and the lowest speeds are 40 or so, so the 100-0 is a much more demanding test than most realize...a 2 minute lap may have 6 braking zones...1 per 20 sec...
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.


Quote:
Originally Posted by ArtPE View Post

it's ALL about E = 1/2 m v^2...the fact that the M3 weighs 300-400 lbs less than the RS4/ISF/C63 has a lot to do with it's braking efficiency, as does tire size...
Actually (as you are pointing out), tire friction and weight are far more important than pistons and calipers . See list at start of post.


Quote:
Originally Posted by ArtPE View Post

99.9% think we are good drivers...0.1% are...and a good driver will make either systeme work, and out-brake 99.9% of us with the 'lesser' system...
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.

Quote:
Originally Posted by ArtPE View Post

wanna brake better? practice and take some schooling...it's a street car
all differences are so minute they are masked by driver skill levels...
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.
earlyapex is offline   United_States
0
Reply With Quote
      08-20-2008, 08:38 AM   #139
earlyapex
Private
 
Drives: 2008 E90 M3
Join Date: Aug 2008
Location: Raleigh, NC

Posts: 81
iTrader: (0)

The OP point is still a good question. This car has an incrediblely complicated/advanced/expensive engine design, perhaps the most sophisticated and flexible chassis/suspension setup of any car, and brakes that don't meet the standards established by the rest of the car. Why?

The answer? Probably some combination of economics and supplier relationships. At least they didn't stick us with a non-dry-sump leaking mass market toyota engine like porsche does with the 911.
earlyapex is offline   United_States
0
Reply With Quote
      08-20-2008, 08:50 AM   #140
footie
Major General
 
footie's Avatar
 
Drives: ????????????
Join Date: Oct 2007
Location: BMW M3 will get a V6TT

Posts: 7,507
iTrader: (0)

Garage List
2008 E92 M3  [0.00]
Heat in it's many forms are the only real issues with taking a car to the track, that is as long as the braking power is up to the job in the first place. Pad temperature, fluid temperature and disc temperature are the thing to concentrate on.

Getting a good air flow around the disc and calipers will aid the first two points, upgrade the fluid and fit braided pipes should help improve pedal feel and reduce the amount of travel over prolonged periods on the track.

The actual design isn't as important, not from trackdays.

Feel free to disagree.

P.S.
Porsche conduct consecutive braking tests from up to 150mph when designing their systems, that might explain why their brakes are regarded the best manufacturer systems in the business.
footie is offline   No_Country
0
Reply With Quote
      08-20-2008, 09:24 AM   #141
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Quote:
Originally Posted by earlyapex View Post
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?
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).
__________________
lucid is offline   United_States
0
Reply With Quote
      08-20-2008, 09:46 AM   #142
ace996
NASA/PDA Instructor
 
ace996's Avatar
 
Drives: E92M3
Join Date: Aug 2008
Location: Long Island

Posts: 284
iTrader: (0)

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.
phenomenal post, really. That just about says it all, but some will still debate just for the sake of debate.
Be good,
TomK
__________________

"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."Μολὼν λαβέ!!
ace996 is offline   United_States
0
Reply With Quote
      08-20-2008, 11:28 AM   #143
earlyapex
Private
 
Drives: 2008 E90 M3
Join Date: Aug 2008
Location: Raleigh, NC

Posts: 81
iTrader: (0)

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).
Fair enough, no scientific test with a control for the placebo effect () but that doesn't mean there isn't a modicum of truth. I can't get 27mpg in sixth gear at 50mph on cruise control in my M3 (i've tried, it's 26mpg BTW).

The basic problem for the M3 is terrible gearing for mileage (and a plain thirsty engine).

Anyway, the vette engine has more power and torque with dramatically less cost and complication, so in terms of the "only as complicated as it has to be" argument in favor of the M3's brake calipers; the M3 engine loses the same argument dramatically.

I'd rather have a badass engine than brake calipers any day, but that doesn't change the fact that some corners were cut and the M3 nuts can't/won't admit it.

Not to mention, the pointlessness of the OP question of, basically, why doesn't the M3 have as good a brakes as my car that costs more than twice as much?

Well, that question pales in comparison to "why doesn't the a brand new $100k 911S come with a dry sump?" I can buy better brakes than a GT3 for $3,500 for my M3 and it would cost the porsche guys more than 10x that to get an engine as trackable as mine.

What corner would you rather have cut?
earlyapex is offline   United_States
0
Reply With Quote
      08-20-2008, 12:02 PM   #144
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Quote:
Originally Posted by earlyapex View Post
Anyway, the vette engine has more power and torque with dramatically less cost and complication, so in terms of the "only as complicated as it has to be" argument in favor of the M3's brake calipers; the M3 engine loses the same argument dramatically.

I'd rather have a badass engine than brake calipers any day, but that doesn't change the fact that some corners were cut and the M3 nuts can't/won't admit it.

Not to mention, the pointlessness of the OP question of, basically, why doesn't the M3 have as good a brakes as my car that costs more than twice as much?

Well, that question pales in comparison to "why doesn't the a brand new $100k 911S come with a dry sump?" I can buy better brakes than a GT3 for $3,500 for my M3 and it would cost the porsche guys more than 10x that to get an engine as trackable as mine.

What corner would you rather have cut?
I actually pretty much agreed with all of that, and expressed similar views earlier in this thread (post #29). I just wouldn't call it "corner cutting", but would rather use design languages such as "trade-off". I am sure the M3 could have been shipped with a better brake system as there is always a better system to be designed/had. But, as I've said earlier, and as you're saying here, probably more than 99.9% of the folks on this forum, including myself, wouldn't really be able to utilize it fully even on a track. The stock system is pretty solid (but does seem to require some minor mods for track work; I'm tired of my brake fluid boiling and will have it flushed this weekend, and might replace lines and pads soon as well) and you get it for a base price of $56k. What else can one ask for? RED calipers I guess...
__________________
lucid is offline   United_States
0
Reply With Quote
      08-20-2008, 12:26 PM   #145
Radiation Joe
Veni Vidi Vici
 
Radiation Joe's Avatar
 
Drives: '11 JB/BBe-6sp-e90
Join Date: Jul 2008
Location: Macungie PA

Posts: 2,749
iTrader: (0)

Garage List
2011 e90 M3-Sold  [4.25]
2003 RS6 - Sold  [0.00]
2009 e90 M3 - Gone  [0.00]
2003 M3 SOLD  [0.00]
old 2002  [5.00]
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).

Don't forget that the Corvette final drive ends up with something less than 2000 rpm at 70 mph. Put that gearing in an M3 and you'll get 28 mpg also. Honestly, I don't understand why BMW doesn't do that with the final gear (6th with MT and 7th with DCT). You can probably hit the speed limiter in the next lower gear anyway.
__________________

Dinan compliment of stuff plus PF rotors and RG63s. Enough for now.
Why, yes. I am an abrasive bastard.
Radiation Joe is offline   United_States
0
Reply With Quote
      08-20-2008, 12:31 PM   #146
Stunnerable
Captain
 
Stunnerable's Avatar
 
Drives: Nissan Rogue, 09 Jet Black M3
Join Date: Aug 2008
Location: Horsham, PA

Posts: 606
iTrader: (0)

Good point.. but why can't they use the same gears and ratios from the DCT in the Manual.. I wouldn't mind shifting more.
Stunnerable is offline   United_States
0
Reply With Quote
      08-20-2008, 12:36 PM   #147
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Quote:
Originally Posted by Radiation Joe View Post
Don't forget that the Corvette final drive ends up with something less than 2000 rpm at 70 mph. Put that gearing in an M3 and you'll get 28 mpg also. Honestly, I don't understand why BMW doesn't do that with the final gear (6th with MT and 7th with DCT). You can probably hit the speed limiter in the next lower gear anyway.
Yep, that would be included in the packaged to packaged comparison I mentioned. With regards to the M3 gearing, if they won't make 6th taller in MT, why not make 3rd, 4th and 5th shorter?
__________________
lucid is offline   United_States
0
Reply With Quote
      08-20-2008, 12:40 PM   #148
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Quote:
Originally Posted by Stunnerable View Post
Good point.. but why can't they use the same gears and ratios from the DCT in the Manual.. I wouldn't mind shifting more.
I posted before seeing this post. Agreed.
__________________
lucid is offline   United_States
0
Reply With Quote
      08-20-2008, 01:43 PM   #149
DJ9
Captain
 
DJ9's Avatar
 
Drives: 2008 E92 M3_SG
Join Date: Feb 2008
Location: San Francisco/Marin County, CA

Posts: 657
iTrader: (0)

Garage List
2008 M3  [0.00]
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.
Very good response!
__________________
-Dave


2008 E92M3-Space Gray
Eisenmann Sport Exhaust_MT/Loaded
DJ9 is offline   United_States
0
Reply With Quote
      08-20-2008, 02:30 PM   #150
Irb Digital
Lieutenant
 
Irb Digital's Avatar
 
Drives: ///M E90 MANual Jerez
Join Date: Aug 2008
Location: FL

Posts: 458
iTrader: (0)

Send a message via AIM to Irb Digital
I just want to say thanks to all for posting. It seems that this thread went to hell and back, and turned out to be extremely informative, mature thread with some awesome arguments for/against BMW's choice on brakes and a lot of other gee whiz info that I enjoy learning, or RELEARNING from my high school and college years.

I stated earlier that I know I wouldn't see the difference, I just like to know I have the best technology available(within reason) of a $70k luxury sports car. It's not a deal breaker, but certainly something I take into consideration when buying a vehicle of this caliber. One thing for sure is upgrading lines and pads would do more for your dollar than any BBK. I never thought that this car should match the track prowess that is in a GT series 911, but it is nice to know if you could extract the max performance of a car, you've got the best equipment available.

I still haven't decided on which vehicle I will purchase, but its pretty much down to the M3 sedan and IS-F. My first choice is the M3, but thats mostly on paper, as I've yet to test drive one. I'm going against my long time preference of a manual, but I can't help but to be extremely impressed and intrigued of these new automated manuals. It will probably come down to money, and the BMW is significantly more expensive once similarly equipped, but if I can get an 09 for a good discount, I'll be finally in one of my long time dream cars. When I was younger there were a few cars I vowed to own:

S2000 : Being a long time F1 fan, everyone raved that this was the closest thing to a poor man's F1 that one could buy. I did get the joy of owning one and haven't driven a better performance car since. The Z I currently own is a better touring car. I bought it because it was more comfortable with my 6ft2in frame, and my convertible days were numbered. The Z just doesn't have the soul or appeal to my senses the way the S2000 did.

Any M series BMW : If they have the balls to call it the "Ultimate Driving Machine", I've got to experience it. Plus, I need to experience what causes all the C&D editors to treat the M3 as God's own chariot. If it happens she's in Alpine White(homage to the F1 team), red interior (homage to the red in the ///M logo).

Ferrari : Explanation not needed

Thanks again for everyone's input
Irb Digital is offline   United_States
0
Reply With Quote
      08-20-2008, 05:21 PM   #151
Radiation Joe
Veni Vidi Vici
 
Radiation Joe's Avatar
 
Drives: '11 JB/BBe-6sp-e90
Join Date: Jul 2008
Location: Macungie PA

Posts: 2,749
iTrader: (0)

Garage List
2011 e90 M3-Sold  [4.25]
2003 RS6 - Sold  [0.00]
2009 e90 M3 - Gone  [0.00]
2003 M3 SOLD  [0.00]
old 2002  [5.00]
Quote:
Originally Posted by lucid View Post
Yep, that would be included in the packaged to packaged comparison I mentioned. With regards to the M3 gearing, if they won't make 6th taller in MT, why not make 3rd, 4th and 5th shorter?
5th is 1:1 and as such is fixed. The other gears have to be adjusted relative to 5th. That's why it's not as simple as changing the final drive.
__________________

Dinan compliment of stuff plus PF rotors and RG63s. Enough for now.
Why, yes. I am an abrasive bastard.
Radiation Joe is offline   United_States
0
Reply With Quote
      08-20-2008, 06:24 PM   #152
MarksM
Dishonorable Discharged
 
Drives: 08 M3 replaced with 11 M3
Join Date: Jun 2008
Location: Is it safe?

Posts: 97
iTrader: (0)

Quote:
Originally Posted by Radiation Joe View Post
5th is 1:1 and as such is fixed. The other gears have to be adjusted relative to 5th. That's why it's not as simple as changing the final drive.
Here try this for gear calculations I think it is correct.

Gear Calculations
MarksM is offline   No_Country
0
Reply With Quote
      08-20-2008, 06:44 PM   #153
Radiation Joe
Veni Vidi Vici
 
Radiation Joe's Avatar
 
Drives: '11 JB/BBe-6sp-e90
Join Date: Jul 2008
Location: Macungie PA

Posts: 2,749
iTrader: (0)

Garage List
2011 e90 M3-Sold  [4.25]
2003 RS6 - Sold  [0.00]
2009 e90 M3 - Gone  [0.00]
2003 M3 SOLD  [0.00]
old 2002  [5.00]
Quote:
Originally Posted by MarksM View Post
Here try this for gear calculations I think it is correct.

Gear Calculations
Very nice.

I have one on my work computer called "speed in gears.xls" Your data sheets look better than mine, though.
__________________

Dinan compliment of stuff plus PF rotors and RG63s. Enough for now.
Why, yes. I am an abrasive bastard.
Radiation Joe is offline   United_States
0
Reply With Quote
      08-20-2008, 08:19 PM   #154
lucid
Major General
 
lucid's Avatar
 
Drives: E30 M3; Expedition
Join Date: Apr 2007
Location: USA

Posts: 8,034
iTrader: (0)

Quote:
Originally Posted by Radiation Joe View Post
5th is 1:1 and as such is fixed. The other gears have to be adjusted relative to 5th. That's why it's not as simple as changing the final drive.
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?
__________________

Last edited by lucid; 08-20-2008 at 08:45 PM.
lucid is offline   United_States
0
Reply With Quote
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 01:45 PM.




m3post
Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST