Found this interesting article related to the aviation-side of braking systems (where carbon/carbon and carbon-composite brakes were originally developed I believe): Carbon fibre-based brakes are made out of so-called carbon-carbon composite material that consists of two components: weaved carbon cloth and a solid carbon (and other things) matrix. The carbon matrix is formed by Chemical Vapour Infiltration (CVI) method. According to this method, a vapour of gases (such as CCl4) are introduced across the [heated] weaved carbon cloth and react on the surface of these fibres with formation of solid carbon phase which has ceramic and silicon in it. This solid carbon phase is the one that plays important role in friction and wear performance of the brakes. The CVI coating is a few microns thick and is fine grained and harder than similar materials produced using conventional ceramic fabrication processes. There is a general wear mechanism for carbon-carbon aircraft brakes proposed in 1988. According to this mechanism, there are two types of wear: Type I. This type of wear happens at low energy conditions, such as aircraft taxiing, or when low pressure is applied during braking. At these conditions, a particulate powdery wear debris are formed. The worn particles cause abrasive wear which is the most damaging mode in terms of brake wear - it's like applying a sand paper over the brakes. The particles are mostly formed by carbon matrix, not carbon fibres. Type II. This type of wear is at high energy conditions, such as in aircraft landing, or when high pressure is applied during braking. The difference is that at these conditions, a smooth friction film is formed on the brakes which serves as a solid self-lubricant. This film protects the brakes, therefore the brakes wear less. Of coarse, the braking efficiency suffers, meaning that the friction coefficient is lower for brakes that have formed such a film. The mechanism of formation of this film is not completely clear, even though its existence was proved many times by many researchers. Usually, the following explanation is offered: under higher braking energy condition, higher pressure and temperature assist deformation of wear particles to form a debris film. The particles do not melt though, but plastically deform (carbon does not melt). Nobody will say anything more definitive about this film formation, although there have been a lot of research done on density, crystalline structure, porosity, microscopy and X-Ray diffraction of these films. However Malhotra did work on silicon barriers on carbon-carbon and also on ceramics, which makes me think that these are important parts of it. Murdie, Don, Wright at the Materials Technology Center (MTC) at Southern Illinois University, USA (later CAFS / Centre for Friction Studies) did most of the work on the aircraft braking systems, thanks initially to those kind folks from BF Goodrich and Aircraft Braking Systems (and thereafter the sponsors look like a who's who of industry). Because carbon is oxidised in air at temperatures as low as 500 degC, the extensive research aimed to improve the oxidation resistance of carbon-carbon composites. CAFS researchers studied the oxidation of carbon-carbon materials. There were two commonly accepted ways to protect these materials against oxidation. The first method makes use of oxidation-resistant coatings, such as SiC (silicon carbide). The major problem with this method is the fact that coatings usually induce stresses and often lead to crack formation. The other method of protecting C-C composites was by using matrix inhibitors, such as boron or boron carbide. They reduce the carbon oxidation by spreading a sealant borate glass within the composite. However, due to their low melting point, such inhibitors introduce temperature limitations for composite applications and are effective only after an appreciable fraction of carbon has been gasified. In the braking process and at high humidity, a carbon composite loses much of its friction property and becomes greasy--more like a lubricant. This could be a problem operationally [he says tongue-in-cheek]. What MTC did, but won't tell anyone, was to develop a third method of protecting against oxidisation by making sure the carbon didn't get too hot. The nano-composite material uses ceramic particles to protect carbon from high heat in an oxidising environment. I reckon that there is silicon in the coating as well. The silicon forms the film and the ceramic retards the heat transfer to the carbon fibres. Their dynamometer testing (because they had one) showed that the ceramic-enhanced carbon composite had about a 20-fold higher coefficient of friction than a standard carbon composite. For certain friction applications, ceramic doped carbon materials exhibit more braking capability. The upper limit comes because as temperature and braking energy rise even higher (like in a rejected take-off), the silicon friction film would break into chunks due to shear stresses and thus expose the ceramic-carbon mix to higher friction and so the wear rate would increase again. The other bad thing that could happen at extremely high energy braking is the ceramic cannot sufficiently slow the heat transfer to the carbon fibres and the carbon heats over 500 degC and starts to oxidise. This is especially critical if the temperature of the total brake system exceeds 1000 degC because that means that the thermal gradient is too steep, the ceramic can't offer enough protection, the carbon fibres get hotter, and the oxidation of the carbon fibres leads to a very rapid degradation of the brakes. In conclusion, high braking pressure leads to a lower brake wear, but only up to a limit. The lower brake wear is due to the formation of the silicon film at high energy braking which serves as a lubricant and protector of the ceramic/carbon brake material. The formation mechanism of the film is the subject of scientific debates, but it's known that it does not form at low energy braking, and it is destroyed at extremely high energy braking. From: http://www.geocities.com/profemery/aviation/carbon_brakes.html
Very interesting. This would imply that CCM brakes will wear less on the track but wear faster on the street.
It wouldn't surprise me, they have an operating temp that they like to work in. At United, we were told the worst thing we could do to our ceramic brakes on the 777 and 747-400 was to use light application when cold. They told us to wait a bit and bite deeper into the pedal to get some heat in them, otherwise you were grinding material at too low an operating temp. Gary
i had a 360 with regular brakes, and now a 430 with ccm. i love the ccm. they seem to stop much quicker. also, my 360 front wheels always had a coating of brake dust on them; with my 430, after 1500 miles, and 3 track days, i have not noticed any brake dust on the front wheels. incredible!---much easier to wash/clean.
The clean part I would agree with, the faster stopping is not so likely. Since even the iron brakes have enough braking power to lock the wheels to the point of antiskid intervention, the limiting factor is tire traction, so the iron brake car will stop as fast as the carbon brake car, at least given equal tires. Maybe not so by the tenth max effort stop, when fade could be an issue with the iron brakes, but for anything but track use there would be little to choose between the two systems. Pedal feel could well be superior with the carbons, but the braking distance wouldn't be any different. Gary
i am no expert on the subject, but having picked up a steel rotor, and then picked up a ccm rotor, there is a substantial weight reduction in the ccm rotor. i would guestimate the steel rotor weighs 25 pounds, the ccm rotor is incredibly light at 5-10 pounds. i believe that part of the increased stopping power is from having to dissipate less rotational energy from the ccm rotors. this unsprung weight is spinning on the wheel at a high rate of speed. i don't remember much of my physics, but i do remember force=mass*acceleration. less mass then less force/energy used up stopping the wheel from turning consequently more force available to stop the car. the equations when you have rotation i believe are even more dramatic. maybe an expert can explain it to us.
We took our F430 around Goodwood race circuit earlier this year. We have the standard brakes on our F430. They are fine for the road and normal driving, and unless your a race driver or someone with a quite large amount of experience, they are fine for the track. Although, you do notice after having had the car on 'Race' and thrashing the nuts off of it, you can smell the brakes a bit when you come off the track. They got pretty toasty and tried a lock up a little on 'Race', but they held themselves fine. Although cleaning off all the brake dust was a bit of a pain afterwards. I can highly recommend that what ever spec your F430 is, its worth taking it around the track. A really good experience (helps if you do a quick session at the beginning of the day to get the racing lines). And start off in 'Sport', then go to 'Race' when your comfortable with the car on the circuit, also try and fill up with 97 Octane fuel or higher. I wouldnt recommend putting it on the CRT setting (no driving aids) unless you had large amount of experience, as I've seen a normal road F430 lock up its brakes and hitting the gravel pit.
Cooked the brakes on my 360 spider at Silverstone but must say the CS CCM brakes are great ... Bit abrasive at times tho Image Unavailable, Please Login
I have different experienced with F430 steel brake ... at the end of the third laps in Thruxton, the brake started to fade after the long almost straight track part that went into chicane, but I am not an experience track driver. I push the car but not really squish it dry. Maybe steel brake only suitable for street or a light track day. Just my 2 cnt ...
I have stock brakes on my '05 430 coupe but am considering CCB's on my '07 that I'll be spec'ing out soon (hopefully!). I've heard that the CCB's squeak on the street, especially when cold. Has anyone with CCB's experienced that? Barry
I have zero squeak on the street and I can say very little brake dusk ... but the temperature here only ranging from about 72-104F ...
Is the brake fade due to the metal getting soft due to heat? Is this the reason CCBs don't suffer as much?
But what is real cost for CCB per mile? I have hear it a couple way. I do prefer th CCB and love the clean wheels on stradale, but my standard 36 has stck and thru two sets of pad But at what cost per mile for the typical street driver that drives agressive on street?
Yeh. I cant say every account I have heard of CCB and standard brakes have been the same, some people like them, some dont. And some people just have different views on them. We thrashed ours, but we arent proffesional racing drivers, so the car has a lot more in it, but when you use it on the circuit, you tend to naturally use the car harder. The brakes might fade a bit because of the heat, as i mentioned earlier. When we came off the circuit, you could smell the brakes, and they where the hottest they've been before. When we had our 996 GT3 at Brands Hatch, one of the instructors we know said that instead of putting on your hand brake, put the car in gear. As when your not on circuit, the heat doesnt transfer through the pads, so when you do go out again, the brakes are cooler and more effective (thats for steel brakes, CCB are a bit different heat wise). Nothing major, but it helps a bit.
Exactly. Plus, I detest brake squeal. Another option (as you mention below) is to brake earlier. HPDEs forbid passing in the braking zones and we are *not* racing. So one loses a couple of seconds (per lap, estimate?). <shrug> Assuming high temp fluid and all else being equal, I agree w/u Scotty. But it's a subjective matter. Harmonyautosport *may* be correct depending on his specific POV. As above; but you bring up two more issues: 1) Tires! Brakes don't stop the car .... tires do. Think about it. 2) Set-up, driving style, suspension, etc. All will affect braking and of course, lap times. For example, my heavily modded 05 Comp Pckg M3 SMG did mid to high 1:34s (onboard video timing w/Racepack support) on Dunlop SP 9000s w/OEM pads (Ferodo) on Brembo BBK. Note: Pre Supercharger. I was giving up lots of speed thru T4, T6 & T7 (was working on it). And not getting hard on the throttle out of turns. So there was lots of room for improvement. Terminal speeds were 135ish on the back straight and 130ish on the front. All I have is 5 laps of onboard video w/my F430. (first was a warm-up and the last was a cool down). 1:35, 1:34, 1:33. Terminal speeds 5mph faster front & back. But I had to start braking at the 450 on the back and the 500 on the front. Why? Suspension and tires boyzngirsl! Braking as I would on my purpose built M3 (begin @the 350 on the back straight) would grind the front end on the F430 .... haaard. Ask Larry Vollum. A recipe for a spin (and at this point i'd be close to 145 indicated). A real .... ahem .... eye opener. Controllable? Yes! But sooner or later? As for tires .... i'm still not used to the ABS characteristics of the F430 but the Potenzas are definitely a prob. They don't last as long as the SP9000s. Nor do they stick better. I have some onboard video of Todd Harris (of Pro Drive Racing) doing 1:19s on a *true* F430 CS. He didn't seem to be pushing hard. On my F430 Tonycan did 1:24s (reportedly). But the above is not a fair example. And questions remain. EG; How many 10/10ths laps on an OEM F430 can one do before tires give out? Etc. BTW; I figure i'm losing about two seconds per lap under braking due to suspension set-up on my F430 in comparison to the M3. And that's w/CCMs! But i'm still faster. So here's looking forward to 07. Oh yeah!!! But you should have seen my passenger's eyeballs popping as I came into the T10 braking zone, front end slamming into the bumps, skid plate grinding away; while the rear oscillates and appears to be coming within a few inches of the wall. Didn't do that too many times but it sure was fun! And expensive: Over $1300.00 in damage (thx to RTGT for the repairs, looks great). PS, sorry I missed you @AR Scotty. Looks like Jin does a great job detailing. Lucky you. ;-) Regards, Richard.
Never, ever, put on the hand-brake after coming off the track. Never! Not sure what you mean mate. The reason we admonish all our students to leave the handbrakes off is to prevent the pads from "welding" to the rotors. HTH. Regards, Richard.
I cant say i have heard of the pads wealding to the discs, but i can see where your coming from. Brakes can sometimes become a bit softer after a few laps (as described by prodrive), which could (may / may not be the reason) be affected by the heat generated. As they brakes are a bit more affective when they arent really hot. So by not having the hand brake on when your not on the track, the heat wont pass from the discs to the pads, thus making the brakes a bit cooler for when you next go out (making them a bit more effective). Im no expert (I could be wrong about the above), but thats what the guy told us, and i've heard it a few other places. Kind Regards, Lewis
Dunno. Never *seen* it happen either. But I would certainly worry about uneven cooling due to brake pad contact at one point in the rotor. For me it's enuff that those whom I respect and admire, strongly advise not to leave the E-Brakes engaged. No *maybe* to it: It's caused by excessive heat. Fluid boils. Pads have a max operating temp. <shrug> Proper operating temp is the key. I hope I don't seem argumentative but your POV is flawed and *will* lead to probs (TTBOMK). 1) If you leave the E-Brake engaged it will not help your brakes come up to operating temp quicker by any appreciable amount. I could write a thesis length reply. Just take my word for it, OK? 2) You *will* risk "welding/warping." EG; uneven material transfer from pad to disk. This results in what some erroneously call warped disks. And it can happen simply by operating the brakes at a very high (relative to proper op temp) heat range. Seldom are the disks truly warped. What happens is the pads deposit material onto the disks which result in uneven contact. And one feels a pulsing in the brake pedal. Etc. Etc. Trust me .... you're wrong. It's cool. I'm often wrong also. WTS: Unlike you .... I am an "expert." Well, at least an RKI <big grin>. Those whom I spend (or spent) lotsa time chatting with are true *experts* and they contradict what you wrote. If you won't take my word .... take theirs. Refs available on demand. ;-) Which "guy." I'd like to check his bona fides. Not to be ****** .... but because he contradicts everything i've ever learned about proper brake usage. Understood. OTOH, I can name names. And I am a certified HPDE instructor as well. With 30 years motorsports experience (tho mostly in sportbike racing as a sponsor, team owner, etc). I include one AMA national champion and some local championships thru my sponsored riders (or owned teams). I've learned a bit about racing bikes and cars. Enuff about me. Just ask for creds and i'll point you to a few folks. Altho I dare say that there are a few sponsors (and others) on this site who would make me look like a piker when it comes to brakes and just about anything else car related. Likewise Lewis. A pleasure chatting w/u. Richard.
