Not really, maximum deceleration is limited by the grip available between the tires and the road (and due to aerodynamic effects). Of course, if you were to use a REALLY horrible brake pad, the coefficient of friction that it would generate could potentially be low enough that the brake system couldn't generate the brake torque required for maximum deceleration. This is exactly what happens during brake fade (pad fade, not fluid boiling). The coefficient of friction falls and the system can no longer generate the torque necessary.

The amount of braking torque necessary for maximum deceleration rises only slightly with speed, due to the additional energy needed to slow down the rotating masses on vehicle (i.e. the wheels and tires, brake discs, driveshafts, though in this equation the wheels and tires dominate). Therefore, for a given vehicle it can be treated as nearly constant. The parameters that influence the torque requirement are the mass (static and rotating), and the rolling diameters of the tires. The ideal distribution of this torque between front and rear is determined by the actual deceleration rate, the wheelbase, the center of gravity height, and the static front/rear weight distribution.

 

I think my PCCbs look really cool . . .

 

What about the weight advantage. People often refer to decreasing unsprung weight being far more valuable pound for pound than shedding sprung weight.

And yes Mexico, they do look very cool.

 

The weight advantage is there, but it's negligible. As I posted earlier in this thread, Walter Rohrl (Porsche's famous test driver) is unaware of any real difference in stopping distance between the stock steel brakes and the the lighter and much pricier PCCB brakes, nor is he certain that he can feel the difference produced by the lower unsprung weight in the yellow calipered composite units. If he can't notice the weight advantage, do you think your average driver honestly can?


Trivia question of the day:

Anyone know which car held the 70-0 braking record for 12 years at 149 feet? It was finally beaten by the Carrera GT's 145 foot stop using R-Compounds.

Hint: It's not German, not light, was on standard street rires when it set the record, and used a mediocre braking system that's been around since 1992/1993.

 

Great info, MSV. Thanks.

 

Every picture I've seen here where there were problems with PCCBs seem to be of 1st generation PCCBs. From what I've gathered, there were multiple issues with the 1st generation PCCBs. It also sounds like Porsche has done a terrible job taking responsibility for them. On the other hand, I have not heard of any problems with the 2nd Gen PCCBs. It seems that the problems were solved and the new ones work great. The opinions I've heard is that the 2nd Generations are good if they come with your car, but not worth buying to add on. Though for different reasons, the best Brembo steel brake kits seem to be a better upgrade for the money.

I have 2nd Gen PCCBs on my car right now and love them. I think it would silly for me to change them out for anything else. However, if the track car I purchase in a few years doesn't come with PCCBs already, I surely won't buy them to add. I will be looking at the best Brembo steel brakes that fit my car. OTOH, Just like with all new technology, I predict future generations of PCCBs will eventually make steel brake systems obsolete.

Do any of you out there with 2nd Gen Porsche PCCBs have any complaints about your brakes?

 

[quote=Divexxtreme]The weight advantage is there, but it's negligible. As I posted earlier in this thread, Walter Rohrl (Porsche's famous test driver) is unaware of any real difference in stopping distance between the stock steel brakes and the the lighter and much pricier PCCB brakes, nor is he certain that he can feel the difference produced by the lower unsprung weight in the yellow calipered composite units. If he can't notice the weight advantage, do you think your average driver honestly can?

I noted your earlier reference, and was partly confused by it. People often notice a change in performance if they get heavier steel wheels for winter tires and then find to that they hurt the responsiveness of their vehicles. Similar but opposite experiences have been reported on this forum with people buying lighter wheels.

Now the GT3 and TT have a newer version of PCCB (Gen 2 1/2 or 3 I guess?), than the much maligned GT2's brakes. Was Rohrl's comments in regard to one of the new vehicles?

Thanks for the interesting debate. Still trying to decide whether to get PCCB's on my turbo.

 

Two points:

-Wheels and tires that are similar in weight to brake rotors will cause a more measurable effect on performance due to the larger surface area of their weight (the weight spreads out further from center than the weight of rotors do). The further from a center an object is, the more it's affected by rotational forces.

If you'd like, I could post something that will show you, at least from an acceleration perspective, how little lighter wheels and tires actually help.

-People naturally tend to exaggerate and inaccurately gauge differences in weight, power, etc...when they change something on their car. It’s what's causes the famed "butt-dyno" effect, and isn't really an accurate method of determining performance increases or losses at all.

Quote:

Originally Posted by brnsrgnI

Now the GT3 and TT have a newer version of PCCB (Gen 2 1/2 or 3 I guess?), than the much maligned GT2's brakes. Was Rohrl's comments in regard to one of the new vehicles?

They were the PCCB's on the 997TT he was test driving.

Quote:

Originally Posted by brnsrgnI

Thanks for the interesting debate. Still trying to decide whether to get PCCB's on my turbo.

Don't get me wrong...I'm all about lighter everything. I try to lighten all of my cars as much as practical. My only point was that people should not expect to stop quicker with PCCB's. That's all.

Do I feel they they definitely have their benefits? Definitely.

Do I feel they give you $8k worth of benefits? No. But that's only my opinion.

 

Thanks, seems to be a well informed one. Good point about the rotational inertia effect being related to the diameter of the mass.

So advantages of PCCB are:
lighter weight
less dust
most likely more mileage,
but potentially more fragile

agree??

 

.....Agree.

 

I LOVE MY BRAKES!!!!! All around they are better in everyway!

 

I agree that the 1st gen PCCB were pretty scary, there were lots of problems, and even complete disc failures.

From what I've seen of the new ones, they are much improved.

The basis of this thread was about a relative stopping distance difference between the PCCB and the iron disc cars. Divexxtreme has rightly pointed out that they won't display a significant difference in this regard.

The advantages are pretty well summarized above, and FWIW if I was ordering a new Turbo or GT3 I'd check the box for PCCB. An interesting note on the 997TT compared to the GT3 PCCB systems...I don't know if any of you have noticed the different caliper positions on the front of the TT vs. the GT3 PCCB cars. This is because they use different calipers between the 2. The TT caliper is based on the one that was used on the front of the CGT, and the GT3 caliper is based on the one that was used on the rear of the CGT. The rear systems on the TT and the GT3 are the same. The piston sizes on the GT3 front caliper are smaller than those in the TT, resulting in more agressive front/rear distribution (a topic that I touched on in an earlier post). Just thought you might find it interesting.

 

Sorry but I forgot to say I have the latest version of them.

 

Boris (PCCB nightmare on pg 2) has the right idea - you don't need PCCB to reduce unsprung weight. For MUCH less money, you can get some good 2-piece conventional rotors (slotted or drilled) and have the same effect. It won't be quite as light as PCCB, but combined with some really light wheels, it will do the job. When my stock rotors wear out, I am going to ones like those PF or Alcons.

 

Has anybody seen actual percentages on ordered cars
PCCB yes or no.

Be interesting to see ratio of reg to PCCB in GT3's vs TT's.