Actual (REAL ) weight savings with PCCB's ?
05-29-2015, 03:15 PM
#16
Nordschleife Master
Calipers are nearly identical, though the PCCB pads are noticeably larger in front:
PCCB
Iron
I look it up- the front pads for iron rotors weigh 7.6 lbs for the set. I didn't find the PCCBs pad weight, but pad area is roughly 15% larger- should work out to about about 1.4 lbs, plus a little for the caliper. Call it just under 2 lbs total- a bit more than I'd estimated above. Splitting hairs, but we should probably say the PCCBs save 37 lbs, not 40. And swapping from a full tread-depth tire to a shaved one will make a bigger difference in terms of feel behind the wheel.
PCCB
Iron
I look it up- the front pads for iron rotors weigh 7.6 lbs for the set. I didn't find the PCCBs pad weight, but pad area is roughly 15% larger- should work out to about about 1.4 lbs, plus a little for the caliper. Call it just under 2 lbs total- a bit more than I'd estimated above. Splitting hairs, but we should probably say the PCCBs save 37 lbs, not 40. And swapping from a full tread-depth tire to a shaved one will make a bigger difference in terms of feel behind the wheel.
05-29-2015, 05:02 PM
#17
First realize that rubber is surprisingly heavy, and it's located way out at the edge of the wheel. Shaving 1/8" of rubber works out to roughly 4 lbs on our width tires, but since it's out at the edge of the wheel as opposed to close to the center, this difference has an outsized effect on moment of inertia (MOI). That 4 lbs is roughly equal, in fact, to the MOI of the entire 14.8 lb PCCB brake disk, meaning it's just as hard to accelerate, turn, etc.
This has a different effect than simple unsprung weight which effects ride, of course, but the flywheel effect on turn-in is often described as being the most noticeable difference for PCCBs- the ease with which the wheel turns.
In terms of this the iron rotors do have a 37% higher MOI than PCCB, but that's only equivalent to roughly 1 mm more tread rubber- not exactly a big difference when viewed this way.
If we then simply focus on "unsprung weight" the difference is also much smaller than first appears. One must keep in mind that the iron rotors lose nearly 2.5 lbs before they hit the wear limit, while PCCBs do not lose nearly as much. Thus looking at the front, worn iron rotors and pads with a shaved tire will cut the absolute weight difference to PCCBs to zero (4 lbs of shaved rubber, 2.5 lbs of lost rotor mass, 1.5 lbs for worn pads, while the calipers and pads were 1 lb lighter to begin with = 9 lbs, where the stock PCCB rotor is ~9 lbs lighter to begin with). This setup will also have a nearly 40% lower moment of inertia than the PCCB setup with fresh rubber, so in virtually every way could be expected to perform better.
I don't find it impossible to believe that some people could tell the difference with PCCBs, and in absolute terms they should be fractionally faster when all else is equal. The difference you're trying to feel, however, is in most ways smaller than fresh vs shaved rubber, particularly with worn vs new rotors and pads. In other words it's really quite small, and in the real world dwarfed for me by other effects such as brake feel, etc.
Throw in the added front downforce the iron rotor generates on the GT4 and I do start to wonder which car would be ultimate faster on fast tracks over a single lap, a worn iron rotor car or a PCCB car...
Where the PCCBs still retain a big advantage is in absolute braking capacity. A 918 equipped with the GT4's iron rotors could dump enough power into them to overheat and fade them. The PCCBs on the other hand have more surface area to shed heat, as well as a higher allowable peak operating temperature. This means you can push them harder before they give up. The GT4, however, has less than half the 918's engine power- likely not enough to practically be able to overheat the standard metal disks. They are after all the same dimensions as you'll find on many cars at Le Mans, so in this instance the PCCB's thermal advantage is somewhat academic. On a 918 however it's clearly not.
Food for thought as you decide how to spend your $$.
Last edited by Petevb; 05-29-2015 at 07:35 PM.
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ace37 (12-09-2021)
05-29-2015, 05:33 PM
#19
Rennlist Member
Thread Starter
It is quite surprising the way it works out. In terms of moment of inertia, which changes turn-in, acceleration, etc, the position of the mass matters more than the quantity, which leads to some surprising results when you look at the wheel and tire package as a system:
First realize that rubber is surprisingly heavy, and it's located way out at the edge of the wheel. Shaving 1/8" of rubber works out to roughly 4 lbs on our width tires, but since it's out at the edge of the wheel as opposed to close to the center, this difference has an outsized effect on moment of inertia (MOI). That 4 lbs is roughly equal, in fact, to the MOI of the entire 14.8 lb PCCB brake disk, meaning it's just as hard to accelerate, turn, etc.
This has a different effect than simple sprung weight which effects ride, of course, but the flywheel effect on turn-in is often described as being the most noticeable difference for PCCBs- the ease with which the wheel turns.
In terms of this the iron rotors do have a 37% higher MOI than PCCB, but that's only roughly equivalent to roughly 1 mm more tread rubber- not exactly a big difference when viewed this way.
If we then simply focus on "sprung weight" the difference is also much smaller than first appears. One must keep in mind that the iron rotors lose nearly 2.5 lbs before they hit the wear limit, while PCCBs do not lose nearly as much. Thus looking at the front, worn iron rotors and pads with a shaved tire will cut the absolute weight difference to PCCBs to zero (4 lbs of shaved rubber, 2.5 lbs of lost rotor mass, 1.5 lbs for worn pads, while the calipers and pads were 1 lb lighter to begin with = 9 lbs, where the stock PCCB rotor is ~9 lbs lighter to begin with). This setup will also have a nearly 40% lower moment of inertia than the PCCB setup with fresh rubber, so in virtually every way could be expected to perform better.
I don't find it impossible to believe that some people could tell the difference with PCCBs, and in absolute terms they should be fractionally faster when all else is equal. The difference you're trying to feel, however, is in most ways smaller than fresh vs shaved rubber, particularly with worn vs new rotors and pads. In other words it's really quite small, and in the real world dwarfed for me by other effects such as brake feel, etc.
Throw in the added front downforce the iron rotor generates on the GT4 and I do start to wonder which car would be ultimate faster on fast tracks over a single lap, a worn iron rotor car or a PCCB car...
Food for thought as you decide how to spend your $$.
First realize that rubber is surprisingly heavy, and it's located way out at the edge of the wheel. Shaving 1/8" of rubber works out to roughly 4 lbs on our width tires, but since it's out at the edge of the wheel as opposed to close to the center, this difference has an outsized effect on moment of inertia (MOI). That 4 lbs is roughly equal, in fact, to the MOI of the entire 14.8 lb PCCB brake disk, meaning it's just as hard to accelerate, turn, etc.
This has a different effect than simple sprung weight which effects ride, of course, but the flywheel effect on turn-in is often described as being the most noticeable difference for PCCBs- the ease with which the wheel turns.
In terms of this the iron rotors do have a 37% higher MOI than PCCB, but that's only roughly equivalent to roughly 1 mm more tread rubber- not exactly a big difference when viewed this way.
If we then simply focus on "sprung weight" the difference is also much smaller than first appears. One must keep in mind that the iron rotors lose nearly 2.5 lbs before they hit the wear limit, while PCCBs do not lose nearly as much. Thus looking at the front, worn iron rotors and pads with a shaved tire will cut the absolute weight difference to PCCBs to zero (4 lbs of shaved rubber, 2.5 lbs of lost rotor mass, 1.5 lbs for worn pads, while the calipers and pads were 1 lb lighter to begin with = 9 lbs, where the stock PCCB rotor is ~9 lbs lighter to begin with). This setup will also have a nearly 40% lower moment of inertia than the PCCB setup with fresh rubber, so in virtually every way could be expected to perform better.
I don't find it impossible to believe that some people could tell the difference with PCCBs, and in absolute terms they should be fractionally faster when all else is equal. The difference you're trying to feel, however, is in most ways smaller than fresh vs shaved rubber, particularly with worn vs new rotors and pads. In other words it's really quite small, and in the real world dwarfed for me by other effects such as brake feel, etc.
Throw in the added front downforce the iron rotor generates on the GT4 and I do start to wonder which car would be ultimate faster on fast tracks over a single lap, a worn iron rotor car or a PCCB car...
Food for thought as you decide how to spend your $$.
Gotta love Jesse !!
05-29-2015, 06:19 PM
#20
Don't forget to factor in the weight savings from how much lighter your wallet is with the PCCB's.
The weight of a paper US note is about 1gram. As the $20 bill is probably the most often carried, the roughly $20k replacement cost for PCCB rotors (parts only) is equal to 1000 $20 bills. That equates to about 2.2 pounds of money spent and is a significant weight reduction. As opposed to the weight of the rotors, a 2.2# savings in wallet weight would certainly be noticeable!
Now, if we were to consider the Morgan dollar at face value, the weight savings would be a tremendous 1177.5 pounds! But that would be ridiculous.
The weight of a paper US note is about 1gram. As the $20 bill is probably the most often carried, the roughly $20k replacement cost for PCCB rotors (parts only) is equal to 1000 $20 bills. That equates to about 2.2 pounds of money spent and is a significant weight reduction. As opposed to the weight of the rotors, a 2.2# savings in wallet weight would certainly be noticeable!
Now, if we were to consider the Morgan dollar at face value, the weight savings would be a tremendous 1177.5 pounds! But that would be ridiculous.
05-29-2015, 06:21 PM
#21
Nordschleife Master
Don't forget to factor in the weight savings from how much lighter your wallet is with the PCCB's. The weight of a paper US note is about 1gram. As the $20 bill is probably the most often carried, the roughly $20k replacement cost for PCCB rotors (parts only) is equal to 1000 $20 bills. That equates to about 2.2 pounds of money spent and is a significant weight reduction. As opposed to the weight of the rotors, a 2.2# savings in wallet weight would certainly be noticeable! Now, if we were to consider the Morgan dollar at face value, the weight savings would be a tremendous 1177.5 pounds! But that would be ridiculous.
05-29-2015, 06:36 PM
#22
Drifting
It is quite surprising the way it works out. In terms of moment of inertia, which changes turn-in, acceleration, etc, the position of the mass matters more than the quantity, which leads to some surprising results when you look at the wheel and tire package as a system:
First realize that rubber is surprisingly heavy, and it's located way out at the edge of the wheel. Shaving 1/8" of rubber works out to roughly 4 lbs on our width tires, but since it's out at the edge of the wheel as opposed to close to the center, this difference has an outsized effect on moment of inertia (MOI). That 4 lbs is roughly equal, in fact, to the MOI of the entire 14.8 lb PCCB brake disk, meaning it's just as hard to accelerate, turn, etc.
This has a different effect than simple sprung weight which effects ride, of course, but the flywheel effect on turn-in is often described as being the most noticeable difference for PCCBs- the ease with which the wheel turns.
In terms of this the iron rotors do have a 37% higher MOI than PCCB, but that's only equivalent to roughly 1 mm more tread rubber- not exactly a big difference when viewed this way.
If we then simply focus on "sprung weight" the difference is also much smaller than first appears. One must keep in mind that the iron rotors lose nearly 2.5 lbs before they hit the wear limit, while PCCBs do not lose nearly as much. Thus looking at the front, worn iron rotors and pads with a shaved tire will cut the absolute weight difference to PCCBs to zero (4 lbs of shaved rubber, 2.5 lbs of lost rotor mass, 1.5 lbs for worn pads, while the calipers and pads were 1 lb lighter to begin with = 9 lbs, where the stock PCCB rotor is ~9 lbs lighter to begin with). This setup will also have a nearly 40% lower moment of inertia than the PCCB setup with fresh rubber, so in virtually every way could be expected to perform better.
I don't find it impossible to believe that some people could tell the difference with PCCBs, and in absolute terms they should be fractionally faster when all else is equal. The difference you're trying to feel, however, is in most ways smaller than fresh vs shaved rubber, particularly with worn vs new rotors and pads. In other words it's really quite small, and in the real world dwarfed for me by other effects such as brake feel, etc.
Throw in the added front downforce the iron rotor generates on the GT4 and I do start to wonder which car would be ultimate faster on fast tracks over a single lap, a worn iron rotor car or a PCCB car...
Food for thought as you decide how to spend your $$.
First realize that rubber is surprisingly heavy, and it's located way out at the edge of the wheel. Shaving 1/8" of rubber works out to roughly 4 lbs on our width tires, but since it's out at the edge of the wheel as opposed to close to the center, this difference has an outsized effect on moment of inertia (MOI). That 4 lbs is roughly equal, in fact, to the MOI of the entire 14.8 lb PCCB brake disk, meaning it's just as hard to accelerate, turn, etc.
This has a different effect than simple sprung weight which effects ride, of course, but the flywheel effect on turn-in is often described as being the most noticeable difference for PCCBs- the ease with which the wheel turns.
In terms of this the iron rotors do have a 37% higher MOI than PCCB, but that's only equivalent to roughly 1 mm more tread rubber- not exactly a big difference when viewed this way.
If we then simply focus on "sprung weight" the difference is also much smaller than first appears. One must keep in mind that the iron rotors lose nearly 2.5 lbs before they hit the wear limit, while PCCBs do not lose nearly as much. Thus looking at the front, worn iron rotors and pads with a shaved tire will cut the absolute weight difference to PCCBs to zero (4 lbs of shaved rubber, 2.5 lbs of lost rotor mass, 1.5 lbs for worn pads, while the calipers and pads were 1 lb lighter to begin with = 9 lbs, where the stock PCCB rotor is ~9 lbs lighter to begin with). This setup will also have a nearly 40% lower moment of inertia than the PCCB setup with fresh rubber, so in virtually every way could be expected to perform better.
I don't find it impossible to believe that some people could tell the difference with PCCBs, and in absolute terms they should be fractionally faster when all else is equal. The difference you're trying to feel, however, is in most ways smaller than fresh vs shaved rubber, particularly with worn vs new rotors and pads. In other words it's really quite small, and in the real world dwarfed for me by other effects such as brake feel, etc.
Throw in the added front downforce the iron rotor generates on the GT4 and I do start to wonder which car would be ultimate faster on fast tracks over a single lap, a worn iron rotor car or a PCCB car...
Food for thought as you decide how to spend your $$.
05-29-2015, 07:17 PM
#23
Thanks. I edited the above to include the following to make clear that PCCBs are not without benefit in some situations. The only problem from the pocketbook's perspective is that place you'll find this benefit is the same place you'll be eating your PCCBs at a tremendous rate: extremely high temperatures. The bit I added:
Originally Posted by Petevb
Where the PCCBs still retain a big advantage is in absolute braking capacity. A 918 equipped with the GT4's iron rotors could dump enough power into them to overheat and fade them. The PCCBs on the other hand have more surface area to shed heat, as well as a higher allowable peak operating temperature. This means you can push them harder before they give up. The GT4, however, has less than half the 918's engine power- likely not enough to practically be able to overheat the standard metal disks. They are after all the same dimensions as you'll find on many cars at Le Mans, so in this instance the PCCB's thermal advantage is somewhat academic. On a 918 however it's clearly not.
05-29-2015, 07:26 PM
#24
Racer
Wow Petevb, that's some incredible rationale! Ortho, you schooled me on how the reasonable track junkie would never run PCCBs. I can't say enough how I appreciate this sort of detail, provided for free by fellow enthusiasts. I will never have the time, expertise, or the patience to contribute as you and others have and I just want to say thanks 
I'm getting the PCCBs anyway
I'm only 10-12 trackdays per year. I have <13,000 miles on a 2012 CR and I flog those brakes at every stop. I've had two steel cars and the composites I just like better. I get warm and fuzzy feelings everytime I look at them and that's worth every extra dime to me. Wheels always look clean and having just replaced my front pads last week, I think $600-ish is a small price to have these so far. This is MY driving habits and this works for ME. The overall look of these huge rotors is also irresistible and I don't really like the color red to begin with. But that's just me...
Would I pay the equivalent of replacement price to have them specced on a new car? Not a chance. Would I get them for a car slated primarily for track use? No way. Orthojoe has taught me better and Petevb just blew me away with all that unsprung weight/ factual-stuff. Amazing!
I'm getting the PCCBs anyway
I'm only 10-12 trackdays per year. I have <13,000 miles on a 2012 CR and I flog those brakes at every stop. I've had two steel cars and the composites I just like better. I get warm and fuzzy feelings everytime I look at them and that's worth every extra dime to me. Wheels always look clean and having just replaced my front pads last week, I think $600-ish is a small price to have these so far. This is MY driving habits and this works for ME. The overall look of these huge rotors is also irresistible and I don't really like the color red to begin with. But that's just me...Would I pay the equivalent of replacement price to have them specced on a new car? Not a chance. Would I get them for a car slated primarily for track use? No way. Orthojoe has taught me better and Petevb just blew me away with all that unsprung weight/ factual-stuff. Amazing!
05-29-2015, 07:44 PM
#25
I was reading a thread earlier, and when push came to shove, it seemed that the actual weight savings were, not that significant...??
Also if one was interested in tracking the car at times ( and another set of wheels were desired, going to a smaller 19 inch, which would allow for a more vast tire selection) one's options would be very limited , as they, the PCCB's would not accommodate a smaller 19 inch wheel.....
Do I have all of the correct ??
Also if one was interested in tracking the car at times ( and another set of wheels were desired, going to a smaller 19 inch, which would allow for a more vast tire selection) one's options would be very limited , as they, the PCCB's would not accommodate a smaller 19 inch wheel.....
Do I have all of the correct ??
Maybe not, Forgeline supposedly has a 19" that will fit (according to my local Forgeline dealer) over the PCCB. I ordered a set about 4-5 weeks ago. They are in production and should ship the end of next week. When they get here, we will have them test fit to the car. My wheel supplier tells me that Someone(s), don't know who, I would have thought they might be on Rennlist, had been testing the wheel fitment since sometime late last year. Bueller?
As re: the weight saving, I think it's "substantial" but. . . . it's also not just the gross weight alone that is important. The weight (mass) distribution is also relevant. The CCB at 410mm in diameter puts some of the rotor weight farther from the axis of rotation, and that has an effect on the whole wheels "moment of inertia" balance.
Never mind, just went back thru the thread and Petevb's said it all better.
05-29-2015, 07:49 PM
#26
Rennlist Member
FWIW it was during a casual conversation
05-29-2015, 07:51 PM
#27
Very much looking forwards to your next round of PCCB measurements, which I think are the best measure we have so far of real Gen 3 PCCB wear, and the basis for much of running costs math we're working on. Thanks for doing that.
Last edited by Petevb; 05-30-2015 at 03:39 AM.
05-29-2015, 07:55 PM
#28
Rennlist Member
Maybe not, Forgeline supposedly has a 19" that will fit (according to my local Forgeline dealer) over the PCCB. I ordered a set about 4-5 weeks ago. They are in production and should ship the end of next week. When they get here, we will have them test fit to the car. My wheel supplier tells me that Someone(s), don't know who, I would have thought they might be on Rennlist, had been testing the wheel fitment since sometime late last year. Bueller?
As re: the weight saving, I think it's "substantial" but. . . . it's also not just the gross weight alone that is important. The weight (mass) distribution is also relevant. The CCB at 410mm in diameter puts some of the rotor weight farther from the axis of rotation, and that has an effect on the whole wheels "moment of inertia" balance.
Never mind, just went back thru the thread and Petevb's said it all better.
As re: the weight saving, I think it's "substantial" but. . . . it's also not just the gross weight alone that is important. The weight (mass) distribution is also relevant. The CCB at 410mm in diameter puts some of the rotor weight farther from the axis of rotation, and that has an effect on the whole wheels "moment of inertia" balance.
Never mind, just went back thru the thread and Petevb's said it all better.
There really is a very small gap from the caliper to the wheel. I've already had a rock grind up my wheel & dig into my caliper with my PCCB's on 20s, can't imagine what it would be like with 19s on there. I'd expect it to effect brake cooling quite a bit too.
Very interested to see how the wheels turn out for you!
05-29-2015, 08:29 PM
#29
Nordschleife Master
Thanks. I edited the above to include the following to make clear that PCCBs are not without benefit in some situations. The only problem from the pocketbook's perspective is that place you'll find this benefit is the same place you'll be eating your PCCBs at a tremendous rate: extremely high temperatures. The bit I added:
05-30-2015, 02:51 AM
#30
Rennlist Member
Thread Starter
Maybe not, Forgeline supposedly has a 19" that will fit (according to my local Forgeline dealer) over the PCCB. I ordered a set about 4-5 weeks ago. They are in production and should ship the end of next week. When they get here, we will have them test fit to the car. My wheel supplier tells me that Someone(s), don't know who, I would have thought they might be on Rennlist, had been testing the wheel fitment since sometime late last year. Bueller?
As re: the weight saving, I think it's "substantial" but. . . . it's also not just the gross weight alone that is important. The weight (mass) distribution is also relevant. The CCB at 410mm in diameter puts some of the rotor weight farther from the axis of rotation, and that has an effect on the whole wheels "moment of inertia" balance.
Never mind, just went back thru the thread and Petevb's said it all better.
As re: the weight saving, I think it's "substantial" but. . . . it's also not just the gross weight alone that is important. The weight (mass) distribution is also relevant. The CCB at 410mm in diameter puts some of the rotor weight farther from the axis of rotation, and that has an effect on the whole wheels "moment of inertia" balance.
Never mind, just went back thru the thread and Petevb's said it all better.
Yea I am just going to go with the steel ...
I just want the damn car so bad ...I feel like a child wanting his ice cream !!
Best regards
Ed