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      08-18-2008, 09:11 PM   #111
swamp2
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Drives: E92 M3
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Quote:
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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