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      12-02-2008, 06:25 AM   #42
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Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

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Originally Posted by lucid View Post
I don't see the need to respond to the details of your last post. And to try to keep things collegial, I won't refer to your language as "rattle", but do go over your posts to see the tone you used in this exchange.
I chose my tone clearly based on your jabs big guy, tit for tat.

Originally Posted by lucid View Post
You have once again avoided the issue, the clear question I posed, and actually answered, which is simply: How does the kinetic energy of the vehicle end up in the rotor? How does the rotor experience the temperature change the conservation of energy equation dictates? Through what mechanism exactly?
Wait a second friction generating heat, isn't that absolutely common grade school knowledge??? The conversion of energy into heat. Again we must not be communicating, as this is the answer to the question you are asking. I really did not think it warranted a reply.

Originally Posted by lucid View Post
The question has been answered by a domain expert, a scientist, as well in a well respected peer reviewed journal. The man has written a dissertation and a book on the topic and who knows what else, and you question the validity of his explanation--that one needs to increase conductivity to control friction surface temperatures. You think this explanation would have been published in a peer reviewed journal if it was false? Something as basic as that, simply wrong?

Let's see. Who is more credible here? A well-respected and published scientist, who specializes in this specific area, or Swamp, who has worked on mountain bike brakes for two years (not to discredit your experience in that domain, but that is a different domain, a different ball game).
Nope I don't question this particular point. Any effort in any material to increase lateral conductivity will help limit peak temperatures and hence reduce fade. BUT... THIS IS NOT THE QUESTION WE ARE ASKING IT IS SIMPLY ONE SECONDARY EFFECT IN DETERMINING THE PAD TEMPERATURE FOR THE SYSTEMS AND TO THEN COMPARE THOSE TO THEIR RESPECTIVE LIMIT TEMPERATURES. It is again nearly common knowledge and something that was part of my very first explanation saying that you needed to "average" and that there are "second order effects". As you might know the source of all of this emphasis on conductivity of CSiC materials is because many initial materials and perhaps even initial PRODUCTS had a very poor lateral conductivity which only FURTHERS the higher surface temperatures and hence causes the onset of fade EARLIER! You can think of this as part of the rotor - the interior - what should be very "valuable" thermal mass being so insulated from the surface that is does not even participate in the conservation equation. What happens - EARLIER FADE!!

But back the THE expert:

-Who is stating a fact without providing any evidence whatsoever?

-Who is stating a scenario while being terribly (inexcusably IMO) vague with regards to which exact systems are being compared? We've already been through this ourselves and you know you can not make a blanket statement here that all CSiC rotor based systems are superior in terms of fade. Again they are not magic materials. IT IS THE PAD THAT IS ALMOST FOR SURE THE LIMITING FACTOR.

-These massive shortcomings point out excessive marketing and either being light on the science or seriously heavy on the confidentiality.

-I am not calling the experts wrong I am simply saying they may not be universally correct.

-I figured you would pull the punch on bikes being different than cars. But you know what, you are categorically incorrect. That is the good thing about physics as compared to engineering. Physics is universal and conservation of energy is universal as well. And finally disc brakes are disc brakes are disc brakes. They convert kinetic energy to heat by friction, period. Grab a copy of the brake handbook and argue with this "domain expert" if you like.

Originally Posted by lucid View Post
As to your question, I have already answered it. The ultimate temperature gain of the entire rotor will be governed by the conservation of energy equation (which should also account for whatever energy that is transfered to the environment via convection during braking as well). However, the friction surface temperatures will be dictated by how fast you can transfer the energy that is being generated at the surface elsewhere, which is dictated by the conductive heat transfer principles I've been outlining all along, deltaT (temperature difference between the friction surface and the vented surface of the disc) and conductivity. The temperature distribution throughout the rotor is the key issue here. You want that to be uniform as possible during braking (and it clearly will not be uniform) to achieve the lowest friction surface temperatures.
Well we almost have some agreement. But you keep missing the forest for the trees. We agree surface temps are higher during braking and before equilibration, however this is a second order effect and it is not unreasonable to approximate "the" rotor temperature by the spatial average of it. Either way, with any rotor that has a higher surface temperature will simply cause such a system to fade a bit earlier than the conservation equation predits. Finally, to truly compare two systems we must have the friction-temperature curve for a typical CSiC rotor-pad matched set and it seems you may be coming around to this idea. As well it seems you are coming around the the validity of the conservation equation. As you first called it an "over generalization" and "inaccurate" but now state is it yourself just above as a definitive part of a calculation based approach to answering this question.

I'm still sticking firmly to my points #1-#3 from many posts back. I haven't heard any specific disagreement to those yet. If you believe identically as your infallable expert that categorically all CSiC systems provide superior fade resistance you should be disputing my item #1.