PCCB vs Factory steel brake weight difference??
02-28-2015, 11:31 PM
#46
Rennlist Member
Thread Starter
I couldn't agree more with what you are saying, Nova.
My case in point -- my '06 Cayman S has a set of wider-than-stock, and quite heavy (though very pretty) cast wheels, Roderick RW5's with wider, meaty Nitto Invo tires. When my '12 Cayman R was delivered and I took it out for a spin, I immediately noticed how the car seemed to just dance over bumps compared to my S. Felt like a ballerina tiptoeing across the stage compared to Herman the Munster hammering his feet on the ground. The difference was night and day. Of course the R felt a lot more powerful too -- but that's a different story with other contributing factors (engine, tranny, exhaust) than purely unsprung weight.
Some time later when I was changing tires I weighed the mounted rims on the S vs the R. The R, with its lightweight BoxSpy rims and lighter, narrower MPSS tires were 8 pounds lighter in front, 10 pounds rear...
...very very interesting that the Cayman GT will also have about a 10 lb weight difference on each corner - PCCB vs steel rotors...
My case in point -- my '06 Cayman S has a set of wider-than-stock, and quite heavy (though very pretty) cast wheels, Roderick RW5's with wider, meaty Nitto Invo tires. When my '12 Cayman R was delivered and I took it out for a spin, I immediately noticed how the car seemed to just dance over bumps compared to my S. Felt like a ballerina tiptoeing across the stage compared to Herman the Munster hammering his feet on the ground. The difference was night and day. Of course the R felt a lot more powerful too -- but that's a different story with other contributing factors (engine, tranny, exhaust) than purely unsprung weight.
Some time later when I was changing tires I weighed the mounted rims on the S vs the R. The R, with its lightweight BoxSpy rims and lighter, narrower MPSS tires were 8 pounds lighter in front, 10 pounds rear...
...very very interesting that the Cayman GT will also have about a 10 lb weight difference on each corner - PCCB vs steel rotors...
02-28-2015, 11:35 PM
#47
If Röhrl can't feel the difference between PCCBs and iron rotors (not citing Petevb's chat with him, there are other examples of Röhrl mentioning this) and others can, then so be it. Some also think their car is faster since it is painted red or yellow.
03-01-2015, 12:20 AM
#48
But the flywheel effect is not the only difference you would feel, right? That is the effect on acceleration and deceleration. On the other hand, you also have just the total effect on unsprung weight on the suspension. That's what I experienced at least in comparing the 991S with and without PCCB back to back on the street. The car with PCCB was noticeably more composed on roads around here, and that drive made me much more interested in PCCB.
For me the GT4 will be a street and track car. If it were 80% track, I'd go standard brakes probably to avoid risk of going through expensive rotors too quickly. Although, to be honest, if I were going to spend $100k on a dedicated track car it probably wouldn't be a GT4 to begin with.
For a car that will spend a majority of its miles on the street, including to/from tracks, (like mine will) then I go back to that test drive and it makes we want the PCCB. Not because of the flywheel effect on acceleration (in either direction), but just the total unsprung weight and how that felt on normal roads (at least on a 991)
For me the GT4 will be a street and track car. If it were 80% track, I'd go standard brakes probably to avoid risk of going through expensive rotors too quickly. Although, to be honest, if I were going to spend $100k on a dedicated track car it probably wouldn't be a GT4 to begin with.
For a car that will spend a majority of its miles on the street, including to/from tracks, (like mine will) then I go back to that test drive and it makes we want the PCCB. Not because of the flywheel effect on acceleration (in either direction), but just the total unsprung weight and how that felt on normal roads (at least on a 991)
I am by no means claiming that I possess ANY driving skill that Walter Rohrl doesn't, just my impressions and the reason for them.
03-01-2015, 12:26 AM
#49
I would be interested if there was a quote however where he states that he feels NO difference.
03-01-2015, 12:35 AM
#50
Rennlist Member
I wouldn't get PCCBs in this car expecting that it will make the car stop better. And again, if I were looking strictly just at track performance, which is what I suspect Rohrl was actually talking about, I'd probably go standard brakes, no AC and no radio. That would make sense.
But what about a car that won't be my primary DD, but will be one of just 3 cars that I will drive for the next few years? And a car that I will drive hours to and from VIR, etc? That's a very different use case from what Rohrl faces, I would think. Thats why my GT4 (if I manage to get one) will have AC and a radio, and likely PCCBs as well.
03-01-2015, 12:47 AM
#51
Race Director
This is an excellent thread, and petevb's analysis, is as good as we can hope for to give some real understanding of the potential increase in durability on a "lighter" car with "less" power like the gt4.
I've experienced the value of lighter rims on motorcycles going from cast aluminum to magnesium in my track bike and it really was.. Night and day. On the flip side, going to a relatively heavy 19" cast wheel on my BMW makes absolutely thud over potholes and road imperfections.
While getting a lighter wheel than the stock gt4 one may be possible, I remember reading that they make them pretty light to begin with. The implied handling advantage that pccb offers for that car may be a worthwhile expenditure when I consider that
1, they are same size as gt3 but for 25% less cost
2. The aforementioned handling advantage discussed
3. The probably durability increase deduced by petevb
4. The fact that I would use the car mostly on the road (very crappy roads at that) and to go to and from the track maybe 1/month.. Realistically 6/year.
5. The cool factor of having massive 410mm rotors on a "small" car and the oh so sacred for a poseur like me... No brake dust.
Pccb aren't off the table yet.
I've experienced the value of lighter rims on motorcycles going from cast aluminum to magnesium in my track bike and it really was.. Night and day. On the flip side, going to a relatively heavy 19" cast wheel on my BMW makes absolutely thud over potholes and road imperfections.
While getting a lighter wheel than the stock gt4 one may be possible, I remember reading that they make them pretty light to begin with. The implied handling advantage that pccb offers for that car may be a worthwhile expenditure when I consider that
1, they are same size as gt3 but for 25% less cost
2. The aforementioned handling advantage discussed
3. The probably durability increase deduced by petevb
4. The fact that I would use the car mostly on the road (very crappy roads at that) and to go to and from the track maybe 1/month.. Realistically 6/year.
5. The cool factor of having massive 410mm rotors on a "small" car and the oh so sacred for a poseur like me... No brake dust.
Pccb aren't off the table yet.
03-01-2015, 01:57 AM
#52
Guys, I've got no problem with PCCB rotors. I've had my share of non standard rotors. I encourage a blind test drive of both rotor types, there is a lot of psychology involved in this. Weight differences are not as mitigated with PCCB rotors as much as one thinks. The rotational inertia (angular momentum) involved in turning in of larger brakes cancels a lot out. Try moving a bicycle wheel while it is rotating. Then try a larger wheel that is lighter but larger. PCCB / iron rotor weight differences are not as significant to counteract these diameter differences.
When hitting bumps the rotor momentum change will also be faster than the iron disc ones. Just as the recovery would be. I won't get into math, etc. But it's pretty easy to verify this with undergraduate classical physics. No need to pound out Lagrangians.
When hitting bumps the rotor momentum change will also be faster than the iron disc ones. Just as the recovery would be. I won't get into math, etc. But it's pretty easy to verify this with undergraduate classical physics. No need to pound out Lagrangians.
03-01-2015, 03:50 AM
#53
Burning Brakes
Guys, I've got no problem with PCCB rotors. I've had my share of non standard rotors. I encourage a blind test drive of both rotor types, there is a lot of psychology involved in this. Weight differences are not as mitigated with PCCB rotors as much as one thinks. The rotational inertia (angular momentum) involved in turning in of larger brakes cancels a lot out. Try moving a bicycle wheel while it is rotating. Then try a larger wheel that is lighter but larger. PCCB / iron rotor weight differences are not as significant to counteract these diameter differences.
When hitting bumps the rotor momentum change will also be faster than the iron disc ones. Just as the recovery would be. I won't get into math, etc. But it's pretty easy to verify this with undergraduate classical physics. No need to pound out Lagrangians.
When hitting bumps the rotor momentum change will also be faster than the iron disc ones. Just as the recovery would be. I won't get into math, etc. But it's pretty easy to verify this with undergraduate classical physics. No need to pound out Lagrangians.
03-01-2015, 10:12 AM
#54
Rennlist Member
03-01-2015, 02:16 PM
#55
I think there is a decent argument to be made for the PCCB option on the street. Keep in mind that they are expensive performance: even at $7.4k they are still a decent fraction of the price difference between the GT4 and the GT3, and they won't buy you nearly that same fraction of performance difference. There are also other places you could put that money, for example running Trofeo Rs that wear out 2x faster than PSC2s, that will get you more performance. Despite which they are probably worth considering.
Feel is actually a negative for me, because I don't like the over-assisted PCCB pedal feel. I wish Porsche would use a larger master cylinder for PCCBs to counter this; I understand their test drivers would generally prefer a firmer pedal, but customers pull them to a softer one.
Performance there is a slight advantage to PCCBs, but I'm not sure if that's material on the street. If I was running SCCA solo (where the GT4 probably won't be competitive anyway) I'd need to order PCCBs, as they are probably worth .1 to .2 seconds. Similarly I designed adapters and hats to put PCCBs on my '69 due to the unsprung weight advantage- on a light car you can feel it, though the difference will be much smaller than changing tire brands. Keep in mind though that even the PCCBs aren't hugely light- for street duty the regular Cayman's brakes, either steel or 350mm PCCB, would probably be the better choice.
Cost on the street you'd simply need to assume you never replace rotors. If you did the only prices I found were $5k each. The rears are the same diameter and thickness and the Z28's, which might become available at some point for ~$1k each if history holds, so there is a chance those could be fit.
On the track it'd be very difficult for me to justify PCCBs. A set of 19" track wheels would not only cancel out the rotating inertia advantage, it would let you use real track rubber and track brake pads. Converting to lightweight steel Brembo rotors would offer all the performance needed for this application, would cut the PCCB's weight advantage in half, and would be far cheaper to run. If Porsche worked with Michelin/ Pirelli to provide a less streetable 20" tire option for their street cars that could compete with a Hoosier of NT-01 then the PCCBs would be more attractive to guys who track. As it is they effectively lock you into some of the most expensive tires available, so increasing your track running costs even before the rotor bill eventually comes due. Thus unless you're not sensitive to costs or lap times (a strange combination) or running in a class I think guys who track consistently will again skew towards the steel brakes despite the improved trackability and lifespan we can expect from the upgraded PCCBs.
Feel is actually a negative for me, because I don't like the over-assisted PCCB pedal feel. I wish Porsche would use a larger master cylinder for PCCBs to counter this; I understand their test drivers would generally prefer a firmer pedal, but customers pull them to a softer one.
Performance there is a slight advantage to PCCBs, but I'm not sure if that's material on the street. If I was running SCCA solo (where the GT4 probably won't be competitive anyway) I'd need to order PCCBs, as they are probably worth .1 to .2 seconds. Similarly I designed adapters and hats to put PCCBs on my '69 due to the unsprung weight advantage- on a light car you can feel it, though the difference will be much smaller than changing tire brands. Keep in mind though that even the PCCBs aren't hugely light- for street duty the regular Cayman's brakes, either steel or 350mm PCCB, would probably be the better choice.
Cost on the street you'd simply need to assume you never replace rotors. If you did the only prices I found were $5k each. The rears are the same diameter and thickness and the Z28's, which might become available at some point for ~$1k each if history holds, so there is a chance those could be fit.
On the track it'd be very difficult for me to justify PCCBs. A set of 19" track wheels would not only cancel out the rotating inertia advantage, it would let you use real track rubber and track brake pads. Converting to lightweight steel Brembo rotors would offer all the performance needed for this application, would cut the PCCB's weight advantage in half, and would be far cheaper to run. If Porsche worked with Michelin/ Pirelli to provide a less streetable 20" tire option for their street cars that could compete with a Hoosier of NT-01 then the PCCBs would be more attractive to guys who track. As it is they effectively lock you into some of the most expensive tires available, so increasing your track running costs even before the rotor bill eventually comes due. Thus unless you're not sensitive to costs or lap times (a strange combination) or running in a class I think guys who track consistently will again skew towards the steel brakes despite the improved trackability and lifespan we can expect from the upgraded PCCBs.
03-01-2015, 03:44 PM
#56
Burning Brakes
As it is they effectively lock you into some of the most expensive tires available, so increasing your track running costs even before the rotor bill eventually comes due. Thus unless you're not sensitive to costs or lap times (a strange combination) or running in a class I think guys who track consistently will again skew towards the steel brakes despite the improved trackability and lifespan we can expect from the upgraded PCCBs.
We really need to start a thread re non-OEM wheel and tire options (of all sizes) for the GT4, not just 18's.
03-01-2015, 03:55 PM
#57
Correct, but the point is that it'll be very difficult to impossible to fit 19s over the 410mm PCCBs, so choosing those brakes may well in effect eliminate that option.
03-01-2015, 04:38 PM
#58
Race Director
A question from one who would do 6 max track days/yr due to having too many hobbies to follow any of them 100%... So no dedicated wheel sets for the car.. Just using it as a bone stock, arrive and drive machine with minimal extras.
TIRES-how long does a set of these tires last realistically? More specifically, one track day equates to how many road miles? Does one day **** your tires completely or can you drive the track on new tires, enjoy the day, then use them reasonably for 10,000 miles more?
BRAKES-I heard that the stability control or torque vectoring really does a number on rear rotors.. With smooth driving on track, how many days can you get out of a set of steel brakes/pads? I'm trying to estimate what consumables would cost for about 6 days/yr.
FLUIDS: do these need to be flushed (brakes), oil change after a single track day, or can you use a normal maintenance schedule with the occasional track use every 2 months or so?
TIRES-how long does a set of these tires last realistically? More specifically, one track day equates to how many road miles? Does one day **** your tires completely or can you drive the track on new tires, enjoy the day, then use them reasonably for 10,000 miles more?
BRAKES-I heard that the stability control or torque vectoring really does a number on rear rotors.. With smooth driving on track, how many days can you get out of a set of steel brakes/pads? I'm trying to estimate what consumables would cost for about 6 days/yr.
FLUIDS: do these need to be flushed (brakes), oil change after a single track day, or can you use a normal maintenance schedule with the occasional track use every 2 months or so?
03-01-2015, 04:53 PM
#59
Addict
Rennlist Member
Rennlist Member
Aren't the Trofeo R's a pretty good track option? I imagine that they're almost as fast as Hoosiers and far better for commuting to the track (Hoosiers are easily punctured). They come in the exact GT4 sizes. I'm not put off by the tire choices, just their cost. 19's are no bargain either. The 15's on my 911 are so much easier on the wallet.
03-01-2015, 05:20 PM
#60
Burning Brakes
On the subject of brakes: I don't believe that many people with track experience and who expect to track their GT4 will choose the PCCB option. The steel brakes on this car are a PHENOMENAL upgrade from just about everything else that's available for a Cayman! As an example, I'm considering a Brembo "big brake" (350mm) front upgrade kit on my Cayman R for $4,000 (that's just the cost of the parts). The kit uses 4-piston calipers. The GT4 option is nicer. They are so much more capable than the average driver will ever be able to realize, both in sheer braking power and resistance to fade. I would also expect pad life to be reasonably good considering how oversized they are for the weight and power of the car. But that will depend largely on how hard the car is driven and what pad compound is used. As far as appearance goes, the PCCB brakes can't be beat. But for just about every other reason, I'd take steel.
On the subject of tires: One of the reasons I am eager to find aftermarket wheels for my car is because serious track use destroys the finish on wheels. Maybe not after a day or two of track use. But, over time, track wheels start to look like crap. They become subject to tremendous heat which can hurt the finish, and brake dust and other track debris can also be scarring. The OEM wheels look gorgeous and I'm sure they will be extraordinarily expensive. I'd prefer to save the OEM wheels for my street driving and then throw on a set of track wheels and tires that I wouldn't care about thrashing.
On the subject of tires: One of the reasons I am eager to find aftermarket wheels for my car is because serious track use destroys the finish on wheels. Maybe not after a day or two of track use. But, over time, track wheels start to look like crap. They become subject to tremendous heat which can hurt the finish, and brake dust and other track debris can also be scarring. The OEM wheels look gorgeous and I'm sure they will be extraordinarily expensive. I'd prefer to save the OEM wheels for my street driving and then throw on a set of track wheels and tires that I wouldn't care about thrashing.