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      08-18-2008, 09:11 PM   #111
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Originally Posted by Irb Digital View Post
I've been lurking for a while and after seeing all of nonsense going on in here, I figured I would have a go. I'm not an engineer, but that doesn't make me any less or more knowledgeable on this subject. The man asked a legit question that had some very good answers, both for and against BMW's choice for the braking setup. Then some fanboys came out and without anything intelligent started spouting nonsense. I'll try to state this clearly. EVERYONE KNOWS THAT THIS CAR WAS DESIGNED FOR THE STREET. However for the person that plans on tracking this car, like many M owners do, he would like to know why BMW took a less aggresive approach with the brakes. Many know Porsche has more of a track intent in mind, but some lower priced cars don't and they still have some higher technology built into their brakes. One thing I will say is on the racing circuit, Porsche is probably more known for their brakes than any other aspect of their cars. So there's nothing wrong with following their lead. But in my opinion, this was a cost cutting measure, not BMW's far superior expertise in brakes and deciding not to get caught up in the hype. Just like when Ford decided to keep a live axle in the back of the Mustang. They claimed that well most of our customers said they prefer the setup over an IRS due to the superior drag racing abilities and reliability. It was B.S., they did it to keep the cost of the Mustang down. I don't have a problem with this, but don't throw out a line of B.S. Call a spade a spade. This thread got even better when the "engineers" started name calling. It's sad when a group of enthusiasts can't have a decent debate on design and engineering aspects of a performance car. Most of you guys need to grow up, and calm down. Try to have an intelligent conversation where you actually listen to what the other person has to say, and not take an emotional stab at somebody for not having the same opinion as you.

He clearly stated that there was a performance AND aesthetic value to the more expensive brakes and he wanted to know why BMW chose what he believes to be an inferior setup. I'm pretty sure, outside of the fanboys, anyone that takes a subjective approach will probably tell you that the M3's brake setup is inferior to whats currently available on a lot of sports cars today, especially cars in the 70k price range on up.

Its a lot like the engine debate between low tech 2 valve pushrod American muscle V8's and high tech multi cam, 87 valve foreign sports cars. Some people prefer the higher technology in a high performance car, some people prefer the bottom line(i.e. power). I'd be willing to bet some of the snobs would have passed-out if BMW decided to replace the beloved Inline 6 with a relatively heavy 5.7L Single Cam 2 valver that revs out to 6 grand. It would probably get the job done, but its just not the essence of a German sports car. So why is it so hard to accept that BMW might have chosen the low road on brakes? Porsche, Ferrari, etc......don't put these multi piston unobtanium bits on their cars for marketing. Its for performance. You don't see carbon ceramic on cars competing in Grand Am for hype. They put them on these cars because they perform better than what they used to use.


1. It doesn't take an engineer to know that the Car and Driver test does nothing to replicate a track environment. As I'm an avid reader of C&D the first thing I realized when I read this test, was how unlike the track this test is. It's great for someone making 25 emergency stops in 20 second intervals. Who knows when someone would have to do this but this sidesteps many ways a manufacture might try to improve a cars braking performance. For instance this does nothing to show how well a manufacture has directed airflow to the braking system. On a track you never brake to zero, let alone 25 times. You brake from many different speeds, for many different lengths of times. If you were to take the average speed of each vehicle in this test(including stopped time) this average would be MUCH lower then the average speed on a race course. More speed equals more airflow. This is just one obvious aspect of this test that doesn't replicate what a car might see on the track. Since they used a Nismo package on the Z with more body cladding then a Pontiac Aztec, I wouldn't be surprised if airflow was a major issue on the car that the specialized Brembo package can't overcome. Since I own a Z without the Brembo package I can tell you that the brakes are terrible. I can barely get the ABS activate with aftermarket 19 inch wheels and rubber. I can assure you this brembo package out-brakes what I have on the touring model. A better test would be several different brake packages on the same car. In this test they are comparing the overall braking performance of a car, not of a particular system. Except for the 2 911's(one with the PCCB's). In this test they couldn't see a difference between the two because they couldn't get either of them to start fading, not because they both have the same performance. Put these cars in a 24 hour Le Mans, and then tell me if they perform the same. Ask any enthusiast that upgrades his brakes, and tell me if they don't feel a difference. Aside from measuring the increased pedal distance and increased pedal pressure to achieve the same braking results, this test does very little to measure feedback of the brake system which is probably the most important aspect of a braking system.

2. More pistons should mean a more uniform clamping area. I'm sure like gear ratios in a transmission, there becomes a point when more is useless or counterproductive, but even pad/rotor wear is a very important aspect of braking performance. It also has a direct correlation on braking feel. With more pistons pressing down on the rotor you should need less pressure exerted on the pad to get the same braking performance. With lighter carbon ceramic rotors there is less unsprung weight, which also means better performance in all aspects of racing (cornering, accelerating, decelerating, etc..), and also LESS HEAT for the same amount of stopping performance.

Well this is just my .02, its sad that this thread got mauled by a few idiots and some over-reactions. But it is a good question that should've led to a really good discussion.
OK, I'll offer some replies.
  • The original poster did his share of immature name calling as well. I don't think he needs anyone jumping to his defense. He had some correct point and concerns, some patently incorrect ones and a bit of an attitude problem.
  • You seem to have missed the point. Those defending BMW were not doing do from the perspective that BMW specs out a superior overall brake systms to Porshe. The debate was largely on more pistons = better brakes which is simply not true.
  • As far as the magazine test goes it is painfully obvious that they were not trying to duplicate track conditions. But as we all should know heat is the greatest enemy of most brake systems (that are of an overall solid design for a performance vehicle) and this test was absolutely fine in generating that heat an apples to apples fashion (well almost... a heavier car obvisouly generates more brake heating than a lighter one from the same speed - but it typically has heavier rotors to counter that effect as well). Heat is heat, whether generated at speed with cooling or at slower speeds without much cooling. I certainly am not saying cooling is not important - heck it is one of the most important things in a brake system that most completely overlook. So the conclusion is clearly that the overall fade resistance as indicated by these tests would correlate nicely with actual track based fade testing. Obviously the complexity of making an apples to apples track based comparison prevented such a test.
  • More pistons = more uniform clamping area? Maybe, maybe not. It depends much more on the stifness of the caliper body and pad then you might think. So sorry to be blunt, but here some engineering background would be useful. As well your statement about braking pressure and braking feel. It just is not true that these are absolutely correlated with pad area nor piston count.
  • Lastly carbon ceramic rotors will run HOTTER than cast iron rotors, all else being equal, precisely becuase they are lighter. The CC material itself is totally up to resisting this heat and the pad compounds that they use are tailored for this higher heat level as well. Of course when you add complicating factors such as CCR equipped cars likely have better brake cooling it all becomes a bit of a mess. You clearly have the engineering aspect of this point incorrect.

There pushrod analogy is great. BMW brakes are a bit like a modern Vette engine, not to high tech (well the rotors are...) but very functional. Perhaps there was some fanboy-ism here on this thread but overall it was simply solid defense of a good (not world class, but good) product.
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      08-18-2008, 09:22 PM   #112
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Originally Posted by e46e92love View Post
You should have stopped there, because all you did was come on here and spill out more dribble that means pretty much nothing. So for not picking a better thread and coming with more factual information on your first post.

There are plenty of "engineers" on this site, but not enough. The last thing this thread needed was another opinion from someone who doesn't know, and doesn't even own either of the two cars in question.

I concur...

some of what he saids makes no sense, and makes obvious he is no engineer

no matter what brakes, for a given car from a given speed, the same heat is generated...now granted, it's dissapated at different rates, but E = 1/2mv^2 is still 'true' lol

stopping from 100-0 20 seconds apart 35 times is no different than braking on a track from a given speed at a given rate, in fact the 100-0 without cool down may be more demanding of the system....

braking from 100-0 = 10,000 (100^2) units of energy (normalized for car wt)
braking from say 120 to 60 = 10,800 ~ the same...
but a 2 minute lap might have only 2 or 3 hard braking zones, 30-40 sec apart...
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      08-18-2008, 09:30 PM   #113
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Originally Posted by e46e92love View Post
You should have stopped there, because all you did was come on here and spill out more dribble that means pretty much nothing. So for not picking a better thread and coming with more factual information on your first post.

There are plenty of "engineers" on this site, but not enough. The last thing this thread needed was another opinion from someone who doesn't know, and doesn't even own either of the two cars in question.
My post was directed at the original question posed by the OP and others that made good contributions towards it. You should look into doing the same.
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      08-18-2008, 11:39 PM   #114
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Just to get it out of the way, I'm not an accredited engineer, but I help engineer quite a few avionics systems. I've taken a few engineering classes in college as well physics. I certainly don't have any engineering experience in the design of brake systems. So I am by no means an expert on this. I'm just posting my perception of how some of these things work. Most of this has little to do with my passion and knowledge or lack there of motorsports. I've been an avid enthusiast since I was a kid. I'm 28 and have a lot to learn. Hell even when I'm 68 I'll have a lot to learn. Which is one reason why I like to discuss things like this. I value yours and everyone elses opinions/facts that they post in respect to a good discussion on any aspect of motorsports. In the near future I will be purchasing either an E90 M3, an IS-F, or a C63 so I've been lurking the boards to try to glean as much information I can from people with subjective opinions. I usually put more value the negative information I see when I join a board, because this is usually the information that comes without mindless fanyboyism that plagues all forums. I have test driven the IS-F, hard might I add, and I've been able to sit in the M3 E90/E92. I still haven't made up my mind, but that will require seat time, which won't happen until I get back in the U.S.




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Originally Posted by swamp2 View Post
OK, I'll offer some replies.
  • The original poster did his share of immature name calling as well. I don't think he needs anyone jumping to his defense. He had some correct point and concerns, some patently incorrect ones and a bit of an attitude problem.
  • You seem to have missed the point. Those defending BMW were not doing do from the perspective that BMW specs out a superior overall brake systms to Porshe. The debate was largely on more pistons = better brakes which is simply not true.
  • As far as the magazine test goes it is painfully obvious that they were not trying to duplicate track conditions. But as we all should know heat is the greatest enemy of most brake systems (that are of an overall solid design for a performance vehicle) and this test was absolutely fine in generating that heat an apples to apples fashion (well almost... a heavier car obvisouly generates more brake heating than a lighter one from the same speed - but it typically has heavier rotors to counter that effect as well). Heat is heat, whether generated at speed with cooling or at slower speeds without much cooling. I certainly am not saying cooling is not important - heck it is one of the most important things in a brake system that most completely overlook. So the conclusion is clearly that the overall fade resistance as indicated by these tests would correlate nicely with actual track based fade testing. Obviously the complexity of making an apples to apples track based comparison prevented such a test.
  • More pistons = more uniform clamping area? Maybe, maybe not. It depends much more on the stifness of the caliper body and pad then you might think. So sorry to be blunt, but here some engineering background would be useful. As well your statement about braking pressure and braking feel. It just is not true that these are absolutely correlated with pad area nor piston count.
  • Lastly carbon ceramic rotors will run HOTTER than cast iron rotors, all else being equal, precisely becuase they are lighter. The CC material itself is totally up to resisting this heat and the pad compounds that they use are tailored for this higher heat level as well. Of course when you add complicating factors such as CCR equipped cars likely have better brake cooling it all becomes a bit of a mess. You clearly have the engineering aspect of this point incorrect.

There pushrod analogy is great. BMW brakes are a bit like a modern Vette engine, not to high tech (well the rotors are...) but very functional. Perhaps there was some fanboy-ism here on this thread but overall it was simply solid defense of a good (not world class, but good) product.


I might have come off like I was defending the OP in this thread, but he stooped to the same level as some of the others rather quickly. My intent was to defend the question that he posed, as I thought it was a good one, especially since I will possibly be plunking down $70K of my own hard-earned cash. So back to the matter at hand.

I totally agree with you about the CCB systems. They will run hotter than a standard brake system because they are designed to be more effective at higher temperatures. In my long winded post, I totally overlooked this aspect of CCB systems.

I probably failed to get it across properly but I was trying to say that with a rotor that is identical in size but less in weight, less heat/work will be generated/needed to accomplish the same braking results. Also CC has a higher coefficient of friction than standard systems, now considering it has a higher CF, as well as a higher temperature operating range, and much less unsprung weight I see the major advantages of this rather expensive setup.


I also somewhat agree with you on your reply to the piston count. Piston count isn't the only thing that matters. Caliper stiffness and pad flex are also important. I do think that the purpose of multiple pistons is actually to diminish the probability of parts flexing. Maybe not in every application, depending on how well it is built, but given equal force applied to the pad, and equal materials, I believe that multiple pistons will allow the pad to have a more even grip on the rotor. However the difference might be negligable. Since I'm not an engineer that designs brake systems, I don't have any data to support or disprove MY theory. So again this is just my opinion, as I welcome yours.

Now yes C$D did an apples to apples comparison, but this article was brought up in rebuttal to the OP's original thought that the M3's setup is not ideal for the track. My point was, that this article doesn't replicate a track environment, nor does it try too. The article also implies that the PCCB upgrade on the Porsche isn't worth it. But they clearly say that they had a very difficult time in getting any of the performance cars to fade in this test, except for the Brembo equipped Z. Which I can attest the non brembo Z has terrible brakes, and even with this expensive brake upgrade it doesn't seem to perform much better. It makes me question whether its the design of the brake system or the design of the car. This test also says to me that, they (C&D) failed to create an environment to see which 911 failed first, and how much more abuse the more expensive system could take. Also, along with the entirely different braking situations and added airflow cooling one would would see on a track, braking in a straight line does not present a situation that allows the cars that have electronic brake force distribution to be used in their most effective environments. As most of us know, on a track not all braking is done in a straight line. Trail braking, midcorner corrections, etc....place different grip levels on each wheel. These EBD systems allow different brake pressure to be applied to each wheel which means some rotors will be generating more/less heat each lap. As much as Art thinks this test IS the track, I'm just forming examples of how different the track environment is. This is a great test for 25 emergency stops, but there are many different variables that will come into play on the race track that this test can't duplicate.

I appreciate the kind words about the pushrod comment. In the end I do believe they are effective brakes and probably don't give up much to an equivalent multi-piston setup. One of my favorite cars is the Z06, I love the fact that GM can rip 505 ponies out of a car that weighs 3100 lbs, but I'm still a techie at heart, and would choose a lower displacement, higher technology vehicle with the same performance if I could afford the difference. On a car $70k sports car, even if the performance is comparable, I still place a lot of emphasis on tech that goes into a vehicle. Call it bling if you want, but its not bling for others to see, its bling for my own personal emphasis on having the latest technology available.

Last edited by Irb Digital; 08-19-2008 at 12:06 AM.
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      08-18-2008, 11:54 PM   #115
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After talking to a friend today who tracked his M3 this weekend, it seems pretty clear that the M3's stock brakes have good initial stopping power, but suffer significant fade. He stated that after only three hard laps, it got downright scary.

So my question is this, what would be the most economical way of solving this problem?
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      08-19-2008, 12:01 AM   #116
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Originally Posted by TLud View Post
After talking to a friend today who tracked his M3 this weekend, it seems pretty clear that the M3's stock brakes suffer significant fade. He stated that after only three hard laps, it got downright scary.

So my question is this, what would be the most economical way of solving this problem?
Fluid, pads, lines, ducting...in that order,IMHO. Yes, there are plenty of people who will come forth with the above realization in time...that's why you don't see any real race teams with the stock calipers.
For the street, the stock brakes are fine...and they are under maintenance/warrantee...which is cool, but for the track we will require some changes.

I plan on doing the lines/fluid/pads ASAP and then trying to fabricate someproper spindle ducts. If all that fails, then I'll need to go to better calipers.

Be good,
TomK
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      08-19-2008, 12:23 AM   #117
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Fluid, pads, lines, ducting...in that order,IMHO. Yes, there are plenty of people who will come forth with the above realization in time...that's why you don't see any real race teams with the stock calipers.
For the street, the stock brakes are fine...and they are under maintenance/warrantee...which is cool, but for the track we will require some changes.

I plan on doing the lines/fluid/pads ASAP and then trying to fabricate someproper spindle ducts. If all that fails, then I'll need to go to better calipers.

Be good,
TomK
Thanks, Tom. I plan to track my car occasionally and want to have complete confidence in my brakes, so I planned on doing at least the SS lines and better brake fluid. How easy is it to switch pads in and out on race day in the M3? I'd like to be able to switch to high performance pads on race day and switch back for every day driving, so I can avoid the squeaks and maximize cold braking on the street.
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      08-19-2008, 12:30 AM   #118
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Quote:
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How easy is it to switch pads in and out on race day in the M3? I'd like to be able to switch to high performance pads on race day and switch back for every day driving, so I can avoid the squeaks and maximize cold braking on the street.
As I've yet to receive my M3 yet, I can't comment on the car in specifics;however, if it's like all the other sliding caliper designs, it's not too bad...but I wouldn't do it at the track, at least not me.
My friend has a lift and I change pads the day or two before to bed them in and make sure the stock compound deposits are off before going to the track.

Yeah, the race-compound pads are loud and squeal like bloody murder, but that's what makes me switch them back when I return...or else I'd just leave them in all the time.

Be good,
TomK
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      08-19-2008, 03:47 AM   #119
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For track use, Castrol SRF fluid and Pagid RS19 should be enough.

I don't intend to track this car, as it is my daily driver.

I actually experienced brake fade with my stock 996 GT3 brakes at two track days, the problem was related to cooling. On the 997 GT3 they opened holes on the spoiler lip, increased the rotor sizes, added bigger brake ducts, and shifted brake bias to the back.

I think this type of threads are better suited to the Track forum, given the larger number of experienced track drivers there.

Street driving won't show any weakness in the stock brake system. The stock brakes are ok for the street.

My experience with single piston brakes at the track (E36 M3 and S2000) is that it takes an extra effort to modulate them properly, and under/over braking becomes more common compared to multi-piston setups. Being able to modulate the brakes more efficiently will result in faster lap times.
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      08-19-2008, 07:09 AM   #120
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It's about dollars and egos

It's about $$$$$$! Quit pretending like it isn't. BMW is saving money. Do you get 90% of the physics with fewer pistons? Yes. Are they just as objectively effective in most circumstances? Yes. Does Porsche put big reds on their turbos primarily because they recognize ego plays a huge roll in buying a porsche? absolutely (how many porsches are driven on the track?)

So what do you get from more pistons/stiffer calipers? You gain the ability to modulate the brakes more precisely at the edge of lockup (or the edge of abs). Does this matter with street tires on the street with ABS? Not really.

Does it matter with R-comps that generate significantly higher friction rates and skid transitions than most ABS systems are designed to handle? absolutely. You don't want to be into the ABS with slicks as the car will hop around like a teenager on ecstasy at an oakenfold concert. Not a particularly enjoyable experience on the front straight at sebring at 140mph...

More pistons = more control, but we are talking about the edge of the envelope where far less than 1% of these cars ever get.

Porsche saves money too, look at that IDIOTIC (when it comes to the track) wet/dry sump japanese boxster engine they've been putting in the 911 for 10 years.

The equation e=mv^2 has NOTHING to do with proper brake modulation at the edge.

Again, we are talking about very subtle subjective differences in feel and the ability to control the car more precisely at the extreme. Hardly worth the cost for the 99% of porsches and BMWs that never get tracked, but it's a great marketing tool for the balding stockbroker nonetheless.

You are both right, it just depends on which point you are more focused (the ego issue or the brake feel issue).
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      08-19-2008, 05:45 PM   #121
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It's about $$$$$$! Quit pretending like it isn't. BMW is saving money. Do you get 90% of the physics with fewer pistons? Yes. Are they just as objectively effective in most circumstances? Yes. Does Porsche put big reds on their turbos primarily because they recognize ego plays a huge roll in buying a porsche? absolutely (how many porsches are driven on the track?)

So what do you get from more pistons/stiffer calipers? You gain the ability to modulate the brakes more precisely at the edge of lockup (or the edge of abs). Does this matter with street tires on the street with ABS? Not really.

Does it matter with R-comps that generate significantly higher friction rates and skid transitions than most ABS systems are designed to handle? absolutely. You don't want to be into the ABS with slicks as the car will hop around like a teenager on ecstasy at an oakenfold concert. Not a particularly enjoyable experience on the front straight at sebring at 140mph...

More pistons = more control, but we are talking about the edge of the envelope where far less than 1% of these cars ever get.

Porsche saves money too, look at that IDIOTIC (when it comes to the track) wet/dry sump japanese boxster engine they've been putting in the 911 for 10 years.

The equation e=mv^2 has NOTHING to do with proper brake modulation at the edge.

Again, we are talking about very subtle subjective differences in feel and the ability to control the car more precisely at the extreme. Hardly worth the cost for the 99% of porsches and BMWs that never get tracked, but it's a great marketing tool for the balding stockbroker nonetheless.

You are both right, it just depends on which point you are more focused (the ego issue or the brake feel issue).
Now that is a well stated post, whether opinion or fact
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      08-19-2008, 06:42 PM   #122
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e=mv^2 was just being used illustrate the amount of energy that needs to be dissapated under the two different braking situations. Made perfect sense and it does have value.
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      08-19-2008, 08:30 PM   #123
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e=mv^2 was just being used illustrate the amount of energy that needs to be dissapated under the two different braking situations. Made perfect sense and it does have value.
No one was trying to disprove this equation. I might be wrong but I'm assuming it was brought up in reference to the C&D article. This equation does nothing to show how different systems dissipate heat. Or how more airflow on a track help with heat dissipation. Or how in this test there were no elevation changes like you would see on a track. Or how there was no lateral weight transfer and contrary to popular belief, not all braking is done in a straight line. affecting brake pressures on each individual brake if you had an EBD system. The point was there's more variables effecting brake performance between the controlled environment of the C&D test and an uncontrolled environment like the track than just how much work is done. Just looking at e=1/2mv^2 doesn't do much to answer many of the questions discussed in this thread.
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      08-19-2008, 08:41 PM   #124
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Irb: Great post thanks for sharing all of that information about your background and future car choice. I think we see pretty eye to eye here. One small correction though. Heat (energy dissipated) depends only on mass and speed (and yes brake balance if one tire has more grip) the resulting temperature rise then depends on roughly in order the rotor weight, rotor specific heat (how much its temperature increases for a given energy input) brake cooling rate, brake system weight (including caliper and pad), and conductivity out of the system through the fluid route and the hub route. Heat and temperature are far from equivalent - not even the same units nor concept, but common everyday English diction causes confusion here as well.

earlyapex: Great post as well. Welcome to the forum. Keep up the no nonsense style!
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      08-19-2008, 08:44 PM   #125
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Originally Posted by Dascamel View Post
e=mv^2 was just being used illustrate the amount of energy that needs to be dissapated under the two different braking situations. Made perfect sense and it does have value.
of course it does, but it has nothing to do with feel. It's like describing steering feel by reeling off objective facts on tire cross sections and lateral g forces.

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.
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      08-19-2008, 09:38 PM   #126
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treaded tires stop faster than ones with less tread for a given compound and psi...basic physics
RWD
full tread 100%
1 mm 165% (59 m vs 97 m, ~120 ft more)
FWD
100%
1 mm 218%, over twice as long...
in the dry...
look up the differences in the Bosch handbook

pistons have nothing to do with modulation...
it's the fixed caliper that enhances that...no moving mass...
actually a single piston fixed would be the best, but since run-out occurs, it would pulsate badly...
so multi pistons on a fixed caliper will 'ride' the warp...
it's a very simple, basic hydraulic circuit...mech eng 101...more pistons will grip at different levels, they will NOT operate perfectly in synch when paralleled...

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

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...

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...

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...

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...
most basic formula cars use single piston/floating Girlings, iirc...

Last edited by ArtPE; 08-19-2008 at 10:05 PM.
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      08-19-2008, 10:13 PM   #127
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Quote:
Originally Posted by swamp2 View Post
Irb: Great post thanks for sharing all of that information about your background and future car choice. I think we see pretty eye to eye here. One small correction though. Heat (energy dissipated) depends only on mass and speed (and yes brake balance if one tire has more grip) the resulting temperature rise then depends on roughly in order the rotor weight, rotor specific heat (how much its temperature increases for a given energy input) brake cooling rate, brake system weight (including caliper and pad), and conductivity out of the system through the fluid route and the hub route. Heat and temperature are far from equivalent - not even the same units nor concept, but common everyday English diction causes confusion here as well.

earlyapex: Great post as well. Welcome to the forum. Keep up the no nonsense style!
Thanks for the comment and info....

I gotcha, Heat dissipation is like saying energy dissipation dissipation. Temperature dissipation is the correct wording. Here's 2 questions that I was pondering today, its been a long time since Physics so I'm sure some of the engineers can help me.

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?
2. if you were to remove 200lbs from the interior of the car, and add 50 lbs to each rotor, how would this effect brake performance?
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      08-19-2008, 10:21 PM   #128
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I gotcha, Heat dissipation is like saying energy dissipation dissipation. Temperature dissipation is the correct wording. Here's 2 questions that I was pondering today, its been a long time since Physics so I'm sure some of the engineers can help me.

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?
2. if you were to remove 200lbs from the interior of the car, and add 50 lbs to each rotor, how would this effect brake performance?
heat is thermal energy...and it can perform work...

temperature is a measure of heat energy...
the correct term(s) are heat or thermal energy dissipation...

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
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      08-19-2008, 10:28 PM   #129
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OMG!!!

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      08-19-2008, 11:08 PM   #130
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heat is thermal energy...and it can perform work...

temperature is a measure of heat energy...
the correct term(s) are heat or thermal energy dissipation...

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

Thanks for the answers. So it seems heat dissipation is a correct term? Now I can't lie, some of the stuff you say, is right over my feeble mind. Some of the stuff makes sense, and some doesnt(to me). I will just question what doesn't.

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.

2. Now on to the second response, I'm curious to this response, as I was under the assumption that the momentum of the heavier rotor(unsprung weight) would have an inverse affect on performance.

Interesting.....
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      08-19-2008, 11:28 PM   #131
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the M3 will never exceed 110 on most tracks...
...perhaps we are in different locales, but the tracks in my neck of the woods would certainly allow a fairly driven M3 the ability to hit over 120mph:
Watkins Glen
Limerock
Pocono North/South/Double Infield/F-USA
VIR
and a few new ones... I'll be hitting Monticello on Sept26th in the M3.

We'll see how it goes.
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      08-20-2008, 12:03 AM   #132
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I expect to hit 140 mph TWICE at Cal speedway. both followed by hard braking. then a third hard brake from 110.
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