cannga

After re-reading your post, I found the following summary on the pads you recommended. Obviously it's old news for you , but I thought it good info to post.

Also, I notice your subtle warnings:
>>>At this stage we are not worrying about longevity of pad or rotor or the amount of dust.
>>>>Now expect to have to rebed the brakes on an ongoing basis if you go for the more extreme compounds.

So the way to emulate PCCB is to use ceramic pads with the Big Red's steel rotors? The penalty is more wear and tear? This route would be a little difficult for some of us who are not track diehards, and not as "dedicated" time/effort wise. Playing devil's advocate, is this tacit admission that ceramic IS the better braking compound, well at least for the pads??

So for upgrade choices: ceramic pads with Big Red is high maintenance, PCCB is expensive. Wouldn't the ideal solution be that Porsche offer Brembo GT, instead of PCCB, as the upgrade?


>>>>>>>>>>>>>>>>
The following table summarises the properties of the material types and the characteristics of the pad and possible uses.

RS4-2
BLUE (Carbon-based) The most popular material (known as 'Pagid Blue'), RS4-2 gives a good low temperature response. It is very stable with superior modulation and feel. RS4-2 has a medium co-efficient of friction with good pad and disc life. Suitable for many applications especially gravel rally and wet tarmac, where control is needed. 0.4 0.42 0.46 0.49
@550ºC 350-600ºC 650ºC

RS4-2-1
BLACK (Carbon-based) A very stable material with low disc wear. It has a wide operating range with good low temperature performance and low brake noise. Fitted as original equipment on many high performance road vehicles, this is the best all round pad for road use.

RS4-4
ORANGE (Carbon-based) This material has a high friction level especially at high temperature. It is better for high temperature applications than RS4-2 and has a very stable torque pattern. Suitable for rear axle use on Touring Car applications and very popular in Porsche racing.

RS-7
BLACK (Carbon-based) A material developed for use on rear axle of front wheel drive circuit racing cars with low rear axle weight. Lower friction levels help to reduce rear wheel lock.

RS-14
BLACK (Ceramic-based) A high friction, high temperature material with enviable pad life at this level of friction. Very kind to discs, easily modulated and resistant to wheel lock in extreme use. Suitable for Touring Car, WRC, GT and other forms of medium weight single seater race cars that have good levels of grip.

RS-15
GREY (Ceramic-based) The newest material, a development of RS-14 which combines a 20 percent higher friction level with an improved initial bite. RS-15 has a very good life and exceptional release characteristics. It is also very easily bedded in comparison to it's competitors. Suitable for Touring Car, GT and other applications requiring very high levels of friction and high temperature stability.

RS-19
YELLOW (Ceramic-based) This material provides very good performance at all temperatures with immediate brake response. Very stable pad on ceramic base, with excellent fade resistance and low disc wear. Suitable for endurance racing or applications where exceptional life is required.

cannga

*LAST* questioin: Was I wrong with my "theory," ok, let's be realistic, wild guess, that "better initial bite" doesn't reflect on better overall 60-0 stopping distance because in one, braking is at sub ABS-triggering threshold, whereas in the other (60-0 stopping test), it's all out stomping on the brake, with ABS invoked, and tire adherence becoming the limiting factor?

GG06Si

heres a vid that shows the difference http://www.youtube.com/watch?v=fgeMbs2qsVM

frayed

Robin,

Uhhh, let's see. Ceramics can be insulators, conductors, or semiconductors.

PCCBs are an SiC composite containing, SiC/C. I do not know the weight percentages of each species.

Here's more info:

http://www.sglcarbon.com/sgl_t/indus...sigrasic_e.pdf

Here are the thermal conductivity values (SI units) of the relevant materials:

Thermal conductivity of cast iron: 55
Thermal conductivity of graphite: 119-165
Thermal conductivity of silicon carbide: 120
Thermal conductivity of silcon: 150

So, as you can see, based on your litmus test of thermal conductivity, your cast iron gets an F. The PCCB composite has better thermal stability, better thermal conductivity, better abrasion resistance, and is lighter.

Nordschleife

Well, again - do the empirical test - you will find that not only do ceramic composite brakes stand a great deal of heat, they also hang onto it, longer than iron brakes. Remember the trick with the carbon block in the chemistry lab at school (don't do it, you will maim somebody).

That marketing brochure is hardly going to say 'our product is crap'. In fact I think Tom Waits sang a song about it........

The comparative figures they quote are for raw materials not finished products. The short strand nature of the material that is made up into PCCBs does not perform anything like as well as iron.

The reality is that heat management and fagility becomes a significant problem with PCCBs. To the extent that there is continuous discussion on the subject and a number of very unhappy customers.

PAG have managed this problem worse than Ferrari or Mercedes, both of whom have had rotors shatter whilst driving.

I will be interested to see how well the new material performs, they are closer to carbon-carbon but suitable for street driving.

R+C

Nordschleife

In general terms I would agree with you that some kind of ceramic composite pad material is very efficient.

Anybody intere4sted in this subject might like to consider the problem of stopping France's TGV, the world's fastest train. Technically a nightmare, always cold, very heavy, very high speeds and then vholding the train on them....

As far as brake systems go, yes there are top of the line systems available from Brembo, AP and Movit which will offer extremely high performance, at a cost. Running costs, that is replacement of pads and rotors is up to you, but nothing like as expensive as with PCCBs. Also, one of the plusses about the best 6 piston callipers as opposed to 8 piston callipers, is that the pads are much cheaper to replace.

I was testing a very fast, but fairly heavy car and because it was new, I had not driven it particularly hard, but by the time I arrived at the factory to have the brakes replaced, the very expensive OEM rotors were finished, in 1,600 kilometers. The replacemnt rotors, which had a much harder life as they were being tested, lasted 4,000 kilometers before they were remachined, for reuse. Not only did they improve longevity, but they also improved performance.

R+C

Nordschleife

Yes, it applies whether there is ABS or not. However, with PCCBs it appears to be preferable to modify the ABS program to better manage temperature buildup, without detracting from retardation performance. No, I'm not able to expand upon this, the information is proprietary. Although an assideous search will reveal a US based ABS and ESP engineer who might be tempted to talk off the record about what happens.

R+C

Bob Rouleau

Here is a data point. I was at the Champ car race this weekend. By the way, a great show, easily as good as F1 without the secrecy and snobbery. Champ cars have gone back to iron rotors. They were using carbon (not PCCB, full carbon). The reason for the switch was to make braking distances longer so as to make passing under braking easier.

When I asked if this was because the carbon rotors had shorter stopping distances I was told "yes and no, pro race drivers can overheat any kind of brakes, the carbon rotors dissipate heat faster and tolerate the abuse better. There is no difference in the stopping power between iron and carbon on the first few laps but in a 2 hour race, the carbon rotors tolerate the abuse better and don't require the driver to manage the brakes. To sum it up, for the first ten laps on a circuit that needs a lot of brakes, there is no difference, but by lap 20, the carbon rotors still perform and allow shorter stopping distances. To make passes easier, we have gone back to iron which forces the drivers to brake more gently. The longer distances resulting from having to avoid oveheating the iron brakes, gives drivers a chance to pass under braking."

trobarts

Bob
Good point. I wonder then if one has to manage iron rotors in an endurance race and therefore, braking distances get longer during a stent, would there not be a noticable difference in lap times? I don't know that I seen this, however, but perhaps I have not paid enough attention. Certainly if someone has a big lead, they may slow down, but this is also because of engine preservation as well. If there was a significant difference in braking efficiency over the course of these long races, and carbon brakes are that much better, it is likely that it would become a safety issue which would be addressed by the governing body. Just some observations by someone with little if any expertise.

Bob Rouleau

trobarts - I don' think it is a safety issue. The pros know how to manage brakes. I gather that iron rotors prevent them from brutalizing the brakes without consequences. The issue is about being able to pass under braking. With the carobon brakes the cars can CONSISTENTLY slow from 150 MPH to 40 MPH in less than 100 feet! Figure how long in seconds that takes and then try to imagine trying to outbrake the guy in front to pass. I think it works out to a few thousands of a second ... virtually impossible and likely to cause an accident if you try. F1 suffers from the same problem. I also suspect cost is an issue too, Champ car is trying to keep costs reasonable. Having said that, seeing each team with four huge rigs and twenty or more team members makes me think that this is not budget racing!

Nordschleife

the general aim is to find a brake system which you do not have to worry about for the duration of a race. Some teams may have to change brakes during a 24 Hour race, some don't. The best iron rotor systems do not need cdhanging during a race. There can be a trade off, so you might have to use 'thick' 380mm rotors to last an entire 24 hours, whilst you could drop down to lighter 350mm rotors if you were prepared to change during the race. Its a bit like refuelling, do we use a two stop or three stop strategy?

Professional drivers like to take as little as possible out of a car during an endurance race, that includes being kind to the brakes as well as tyres, engine, gearbox, suspension, chassis.... that way they lessen the risk of their team manager requiring the insertion of a stent during their stint.

R+C

cannga

A couple times now you've mentioned the importance of ABS in PCCB. This is new to me. What do you mean by "ABS optimization" and is this optimization important in street (vs. race) cars?

Do you know if Porsche has different ABS "program" (?) when a car is equipped with PCCB? If yes, does it mean it's not a good idea to replace this PCCB rotor with a steel, ok iron , one?

Also, I don't know where to start reading, so if you don't mind, in one paragraph or less why do you keep stressing that carbon is different from PCCB? Again, to play the devil's advocate, they are more similar to each other than either of them to the iron rotor, no? In that sense, isn't PCCB closer to the gold standard?

Thanks and regards,
Can

cannga

It appears you have tested a lot of cars & brakes?

Do you as a test driver ever feel a performance improvement, not in braking but in other parameters such as handling, acceleration, etc., strictly as a result of a reduction in unsprung weight of one brake system versus another, the order of weight difference being 30-35 lbs or so? (Correct me if I am wrong, but I think this is the weight difference going from iron to PCCB in Porsche's case.)

http://www.porsche.com/pccb/default.asp?market=PCGB

Nordschleife

By optimisation I mean that the parameters controlling the ABS system were subtly altered to achieve maximum performance in the holistic sense. This in combination with variations in rotor formulation, pad material and cooling led to signifricant improvements.

This kind of work is hugely expensive


Some Pcars do have slightly differently programmed ABS systems. In a perfect world one would use an ABS system optimised for either PCCB or iron rotors and pad material. We are talking subtle differences here. I think PAG is still feeling its way forward, but that is only an opinion, not a statement of fact.

Racing brake systems tend to be what is known as carbon-carbon. These are fantastic in terms of performance but absolutely hopeless on the street. They are useless until they are warmed up, so wopuldn't be safe for street driving.

PCCBs are a compromise hybrid material, there has been quite a lot written about them, if yoiu dig around.

Exotic brake rotors are almost 'grown' rather than manufactured, the process tends to involve making an unmachined rotor out of some 'smart' material that you proceed to 'infuse' with carbon over days/weekis. The weak original material is replaced by carbon, this isn't all that happens, but it's the process in a nutshell and results in rotors which are consistent in their structure throughout.

PCCBs are composites, involving different materials and chopped strands, their construction is not as consistent as carbon-carbon brakes.

The rotors in the photograph that I posted above are produced in a manner wich is similar to carbon-carbon brakes, and are designed for road and track use.

R+C

Nordschleife

I have tested a few brake systems, yes.

You can certainly feel big differences between lightweight rotors and heavy rotors. The most obvious example is driving over the expansion joints on elevated sections of freeway. Lie with yoiur cheek againt the floor in the footwell and you will know exactly what I mean. There are all sorts of other benefits, for example, the shock absorber system has an easier job, the springs have less to control, there is less to accelerate......

I hope this explains what I might not have made clear originally.

R+C