JOINING weightwatchers.com would be helathier and cheaper (speaking for myself)

 

This is always a laugh line for cyclists. I've seen guys spend hundreds to shave 1/2 pound off a bike that is already 16 pounds

 

NY991, nice article. Thanks!

 

 

Wish the retailer had some hard numbers of things like shorter braking distances, better acceleration, etc. Otherwise I would not have any idea if it is truly worth the money. I could be wrong but Porsche also never published data on how much improvement in things like braking distance, etc. that PCCBs have over conventional Porsche brakes. Dumb question probably since I'm not an engineer, but what happens to a carbon fiber rim if I hit a really nasty pothole. Does it shatter or maintain its integrity like an aluminum rim?

 

Here is what I think: handling and not acceleration and braking are what lighter wheels buy you. Consider:
Reducing the overall weight of the car will improve its ability to accelerate and slow down. So, if each carbon wheel (with tire) weighs 40 pounds less than the stock wheel (a very dubious proposition) , the effect will be about like not having a 160 lb passenger along for the ride. You can extrapolate to get the advantage of hiring a jockey (or a typical F1 driver) compared to whatever you weigh. In a 400 hp car, you would need a stopwatch to measure the advantage in any case.

Reducing the weight of each wheel (with tire) on the other hand, will allow the springs and shocks to better keep the wheel against the ground. Even a much smaller weight reduction per wheel (~5-10 lbs) would have a substantial effect. How much would depend on your spring rates and rebound mappings- but it would not take much for your car to behave better - whenever the wheels move up and down, they will do it faster.

 

After a certain point, the disks and pad play no role in stopping distance. Up to that level of competence their role is vital, but all brake systems level out at the traction provided by the tires. PCCB's do not improve stopping distance relative to ordinary Porsche brakes. That isn't their advantage.

Gary

 

Agreed. I just would like to see some kind of data/hard numbers on or off track. I understand the advantages from a theoretical level.

 

Gary, Porsche says the obverse on braking distances: "PCCB enables shorter braking distances in even the toughest road and race conditions," and I believe it.

http://www.porsche.com/usa/models/91...detail/safety/

I would like Porsche to tell me by how much someday. Ten thousand bucks is a lot to ask for an undefined capability improvement.

 

They don't tell you because the stopping distance advantage (due to lower vehicle weight) is unimpressively small. They dissipate heat faster and should prevent fade and hold up better- but you would have to be going fast in race conditions to get that advantage over the enormously good standard brakes (especially with the S calipers).

The sales literature states clearly: "The key advantage of PCCB is the extremely low weight of the ceramic brake discs, which are approximately 50% lighter than standard discs of similar design and size. As well as enhancing performance and fuel economy, this represents a major reduction in unsprung and rotating masses. The consequence of this is better road holding and increased comfort, particularly on uneven roads, as well as greater agility and improved handling."

 

Yeah, I know and those advantages, which I believe are also quantifiable, are not published. Wonder if the advantage in those other areas is also small.

 

Of all of the effects, the one that you would feel - in comparison to a car with stock steel brake disks, would be the improvement in suspension response. Even a few pounds per wheel is noticeable. The one thing of which I am certain is that improvements to the technology that affects performance has a constant effect: your bank balance gets lighter and you go faster.

 

PCCB advantage is unsprung weight AND no fade. Had them on both of my GT3s (996 and 997) and after a few laps braking is way better than steel. Do not have to be racing but at 7-8 10ths on a technical track they stay predictable. Just need to sty on the black stuff as they are fragile to impact. Another place to save on rotational mass is the flywheel. The RS provides very good "virtual" HP in 1st-3rd gear. Not sure if the LWFW works in non GT versions.

 

Well done ...

 

Chuck beat me to the response, Holmes. In extreme conditions, the brake system is absorbing more kinetic energy that must be dissipated. Each of the systems, from base to S to PCCB, offer an increase in rate of dissipation. All of them can absorb the kinetic energy of a classic road test (80-0 repeated ten times) without blinking. The biggest contribution of carbon-ceramic brakes is the potential to operate at mean temperatures that are much higher than even that road test creates. As you increase the heat in the brakes, their temperature rises. As their temperature rises, they radiate heat faster. As the average energy input per lap is raised, then the average temperature of the brake system is raised. In other words, the faster my laps, the higher the temperature of my brakes. And it will stay that way lap after lap after lap. Unlike a road test, it never stops. Well, not soon.

Special pads and rotors retain their ability at high temps to grip the disk and modulate the drag in a linear way around the levels that produce tire lock-up. Linear modulation is essential for a highly skilled driver, but also for a top ABS system like ours. The PCCB system presumably -- though I haven't tested them on on a road car -- will operate at those higher temperatures. The iron disks and street pads will not. Fluid boils for example, so it is necessary to add cooling capacity if you push iron disks to that extreme. If the PCCB has those mods as well, then the answer is yes. If it does not, then it will just glow more prettily while it boils the fluid.

Now. Does that shorten stopping distances? Well, certainly if you compare the PCCB's with supplemental cooling to an iron disk system that has been driven to temps so high the fluid boils. In other situations... well, it could retain more controllable linearity to that higher temp. If the system is more linear, then ABS or the highly skilled driver will be able to stop sooner by keeping the tires right on their peak braking level of slip.

We're talking about pretty marginal increases in that last case. Ditto the handling improvement of lower unsprung weight. A related small improvement in braking comes from the more consistent clamping force when the tire is held more adroitly against the pavement by that better suspension. We're talking really fine-grained changes now. But of course efficiency is made up of a great many very small increments of improvement. Whether this particular small increment is worth your money is a very personal decision.

But in general, you cannot push modern Porsche brakes to their extreme with sane driving on public roads. And absent those extreme heating conditions, the car is limited in braking distance by the tires you have mounted.

Gary