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      08-18-2008, 11:39 PM   #114
Irb Digital
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Drives: ///M E90 MANual Jerez
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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.




Quote:
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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