to pccb or not to...
#46
05-20-2008, 07:38 AM
Your unsprung weight write up was an insight but I think it was interpreted way too simply. I can’t quite work out nor find the formula of how a 25kg can equal 480 pounds static weight saving you came up with?
http://en.wikipedia.org/wiki/Moment_of_inertia
The simpler approach would go something like this;
997TT; 1580kg/480 = 303bhp per tonne.
Ceramics are 5.6kg per corner lighter but that’s included in the above weight. So are the 18 inch wheels (lighter on a 996TT) versus 997TT 19 inch wheels.
My 996TT; 1540kg/530 = 344bhp per tonne.
Just by having PCBS on your car there is no way you can actually gain 48BHP.
So, back in the real world;
997TT from my friend makes the 100-200kmh run in 8.9 secs.
My 996TT does same run in 7.0 secs dead.
No driver errors.
So it must be those PCBS horses you’ve got are either very hungry or very old and tired indeed?
PCBS are better brakes when hot. Period, no question there. However, they are not as good as steels on the initial bite when cold and are actually less suitable for the street if an emergency situation arises more so if they are wet. They are expensive and racing drivers unless pro’s and or money is no object don’t use them. They produce less dust which is good, but be aware of the first generation as they are not as good – prone to chipping. The bottom line? PCBS are better than steel when hot. However the difference is not night and day. Tests have shown that the stopping distances are similar and I am yet to get fade on my brakes in seriously fast street driving with my steels. However once on the track brakes on a 996TT need to be upgraded whilst the 997TT’s ceramics don’t. But then again the ceramics won’t last you 100K on the track like claimed for the street and the replacement will be very costly. So as always there are horses for courses...
http://en.wikipedia.org/wiki/Moment_of_inertia
The simpler approach would go something like this;
997TT; 1580kg/480 = 303bhp per tonne.
Ceramics are 5.6kg per corner lighter but that’s included in the above weight. So are the 18 inch wheels (lighter on a 996TT) versus 997TT 19 inch wheels.
My 996TT; 1540kg/530 = 344bhp per tonne.
Just by having PCBS on your car there is no way you can actually gain 48BHP.
So, back in the real world;
997TT from my friend makes the 100-200kmh run in 8.9 secs.
My 996TT does same run in 7.0 secs dead.
No driver errors.
So it must be those PCBS horses you’ve got are either very hungry or very old and tired indeed?
PCBS are better brakes when hot. Period, no question there. However, they are not as good as steels on the initial bite when cold and are actually less suitable for the street if an emergency situation arises more so if they are wet. They are expensive and racing drivers unless pro’s and or money is no object don’t use them. They produce less dust which is good, but be aware of the first generation as they are not as good – prone to chipping. The bottom line? PCBS are better than steel when hot. However the difference is not night and day. Tests have shown that the stopping distances are similar and I am yet to get fade on my brakes in seriously fast street driving with my steels. However once on the track brakes on a 996TT need to be upgraded whilst the 997TT’s ceramics don’t. But then again the ceramics won’t last you 100K on the track like claimed for the street and the replacement will be very costly. So as always there are horses for courses...
#47
05-20-2008, 09:48 AM
Interesting analysis. Not sure about your math. For starters, it looks like you are using speculated crank horespower. Could you take both cars to the dyno and get some real awhp dyno numbers. Then the math might start to make more sense. Also, one shouldnt combine roational weight with static weight to determine bhp per tonne. For example do you think that two cars that weigh 3000 pounds and put out the same hp would run the 1/4 mile in equal times if one car had 2000 pounds of static weight and 1000 pounds of rotational weight and the other car had 2800 pounds of static weight and 200 pounds of rotational weight.
#48
05-20-2008, 10:39 AM
When my Reds were new brake dust was an issue but now after 10K miles its not so bad. I do treat my rims with Zymol Wheel Coat and most of the dust hoses off. Also a quick spin around the block after a wash dries up the rotors (+ your car) and eliminates the rust factor which is nothing to be concerned about in the first place. If I don't take it for a quick spin I notice that if I leave the car sitting for a few days the rear pads (from the parking brake) adhere to the rotors and you get a "pop" sound when it unsticks. I do set the handbrake hard which probably contributes to the sticking. Never had Ceramics so I can't give a comparison. Most likely will get them next time around, especially if they come down in price.
#49
05-20-2008, 11:00 AM
I really regret not getting the PCCBs but there was alot of availability problems with them during my order. I even saw a GT3RS on the showroom floor of my dealer with no PCCBs presumably for the same reason, availability problems, dunno how true that was. Oh well, next time definitely going with PCCBs.
#51
05-20-2008, 06:56 PM
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#52
05-24-2008, 04:12 PM
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Join Date: Apr 2008
Location: Covington, Louisiana
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PCCB Physics
My math is spot on for working out bhp/tonne which is the only way to work out what power different weight cars might have. Yes it’s crank. But this is not the discussion here. The debate here is that I am doubtful that the PC brake system by being 5.8kg lighter per corner would give your car 48bhp advantage. I have given you a real world scenario (and believe me it’s not about the pissing match) that my modestly tuned 996TTX50 car @ estimated 530bhp/crank (<>10bhp) walks away from a stock 480bhp/crank PCCB equipped car. No driver error as we also tried it from through gear acceleration. Not to mention my car is manual and the 997TT is auto in sport mode – so more chances for me to ****-up the shift/change. I am just saying that PCCB cannot give you 48bhp advantage in power. Maybe someone who is a physics expert could chime in here and work out exactly what advantage due to PCCB weight saving translated to power you are actually rally getting. I would love to know.
Further on the question of PCCBs vs not, I took a trip down memory lane with my college physics book today and did some energy balance calculations based on the following assumptions.
The kinetic energy of 4 steel discs at a selected speed minus the kinetic energy of 4 ceramic discs at the same speed gives the incremental kinetic energy that must be supplied by the engine to reach the selected speed with the heavier steel discs. The incremental kinetic energy divided by the time required to reach the selected speed determines the average incremental HP required to reach that speed with steel discs (energy change per unit time = power). For simplicity, it is assumed that sufficient power is available to reach the selected speed in the same elapsed time with either type of disc.
So keep that in mind for the moment. The incremental HP required with steel discs vs. ceramic discs to get to some selected speed also depends on the time interval taken to get to that selected speed.
Calculation Basis
Weight of 1 steel disc: 11 kg
Diameter of steel disc: 350mm
Weight of 1 ceramic disc (front): 6 kg
Diameter of ceramic disc (front) 380mm
Weight of 1 ceramic disc (rear) 5.5 kg
Diameter of ceramic disc (rear) 350mm
All other unsprung component weights assumed identical (as for the rest of the car).
The kinetic energy of each disc consists of translational energy (forward motion) plus rotational energy (spinning motion).
Translational kinetic energy of the disc = ½mv<SUP>2</SUP> (m = mass of disc, v = forward velocity).
Rotational kinetic energy of the disc = ½Iω<SUP>2 </SUP>(I = moment of inertia, ω = angular velocity)
Moment of Inertia for disc = ½mr<SUP>2 </SUP>(m = mass of disc, r = radius of disc)
Since I needed to calculate the tire (rotor) rpm, I needed the overall tire diameter. I used a wheel diameter of 19 inches and added 2 x times the sidewall height based on the stock tire size. Tire diameter gives me tire circumference (pi x d). From forward speed and tire circumference, I calculated the rotor rpm. From rotor rpm, I calculated angular velocity.
Results
Case 1: 60 mph in 3.4 seconds Incremental power = 3.5 HP
Case 2: 100 mph in 7.9 seconds Incremental power = 4.2 HP
Case 3: 60 mph in 10 seconds Incremental power = 1.2 HP
Case 4: 100 mph in 20 seconds Incremental power = 1.7 HP
So there is a small benefit in HP consumption with ceramic discs and the benefit is highest for the maximum acceleration cases. For cases with less than maximum acceleration, the HP advantage becomes smaller which is what would be expected.
Since torque is the change in angular momentum per unit time, a steel disc requires double the torque of a ceramic disc (of the same diameter) to spin it up to the same speed in the same time interval. To put the torque value into perspective, for a single steel disc (front) the torque required to spin it up to 60 mph equivalent rotational speed in 3.4 seconds is about 3 ft-lbf (total available max torque is 460 ft-lbf without overboost on a stock TT).
Also, the rule of thumb of 10 lbs weight savings = 1HP looks about right, at least for small incremental weight savings. A weight savings of 21 kg (46 lbs) for 4 ceramic discs gives a HP advantage of around 4 HP (see Cases 1 and 2 above).
Somebody let me know if all this sounds reasonable. If anybody is interested, I have all this on an Excel spreadsheet.
My head really hurts now and I'm going to stop. I think I pulled a muscle in my brain.
#53
05-24-2008, 04:29 PM
With the additional 100+hp, the powerful breaks definitely compliments the extra power.
I am not sure what after market brakes would compare. But, I would make that an upgrade plan in the future.
enjoy...
#54
05-24-2008, 04:37 PM
Your unsprung weight write up was an insight but I think it was interpreted way too simply. I can’t quite work out nor find the formula of how a 25kg can equal 480 pounds static weight saving you came up with?
http://en.wikipedia.org/wiki/Moment_of_inertia
The simpler approach would go something like this;
997TT; 1580kg/480 = 303bhp per tonne.
Ceramics are 5.6kg per corner lighter but that’s included in the above weight. So are the 18 inch wheels (lighter on a 996TT) versus 997TT 19 inch wheels.
My 996TT; 1540kg/530 = 344bhp per tonne.
Just by having PCBS on your car there is no way you can actually gain 48BHP.
So, back in the real world;
997TT from my friend makes the 100-200kmh run in 8.9 secs.
My 996TT does same run in 7.0 secs dead.
No driver errors.
So it must be those PCBS horses you’ve got are either very hungry or very old and tired indeed?
PCBS are better brakes when hot. Period, no question there. However, they are not as good as steels on the initial bite when cold and are actually less suitable for the street if an emergency situation arises more so if they are wet. They are expensive and racing drivers unless pro’s and or money is no object don’t use them. They produce less dust which is good, but be aware of the first generation as they are not as good – prone to chipping. The bottom line? PCBS are better than steel when hot. However the difference is not night and day. Tests have shown that the stopping distances are similar and I am yet to get fade on my brakes in seriously fast street driving with my steels. However once on the track brakes on a 996TT need to be upgraded whilst the 997TT’s ceramics don’t. But then again the ceramics won’t last you 100K on the track like claimed for the street and the replacement will be very costly. So as always there are horses for courses...
http://en.wikipedia.org/wiki/Moment_of_inertia
The simpler approach would go something like this;
997TT; 1580kg/480 = 303bhp per tonne.
Ceramics are 5.6kg per corner lighter but that’s included in the above weight. So are the 18 inch wheels (lighter on a 996TT) versus 997TT 19 inch wheels.
My 996TT; 1540kg/530 = 344bhp per tonne.
Just by having PCBS on your car there is no way you can actually gain 48BHP.
So, back in the real world;
997TT from my friend makes the 100-200kmh run in 8.9 secs.
My 996TT does same run in 7.0 secs dead.
No driver errors.
So it must be those PCBS horses you’ve got are either very hungry or very old and tired indeed?
PCBS are better brakes when hot. Period, no question there. However, they are not as good as steels on the initial bite when cold and are actually less suitable for the street if an emergency situation arises more so if they are wet. They are expensive and racing drivers unless pro’s and or money is no object don’t use them. They produce less dust which is good, but be aware of the first generation as they are not as good – prone to chipping. The bottom line? PCBS are better than steel when hot. However the difference is not night and day. Tests have shown that the stopping distances are similar and I am yet to get fade on my brakes in seriously fast street driving with my steels. However once on the track brakes on a 996TT need to be upgraded whilst the 997TT’s ceramics don’t. But then again the ceramics won’t last you 100K on the track like claimed for the street and the replacement will be very costly. So as always there are horses for courses...
I don't know much about the physics of ceramic brakes. I can only tell you this. I drove my 997s for 3 years with the red brakes. I swore that I would not spend the extra 8500 for the ceramics. Then I test drove a 997TT with ceramics. I was actually sold on the breaks!!! It was so much more responsive. I could accelerate and I had no doubts that I could stop that car in no time! I really felt this way and I could tell the difference driving my 997s back home. Do you know how these breaks rate on stopping distances? If you have not driven a car (preferably a 997s) with ceramics, you have to try them.
#55
05-24-2008, 05:34 PM
Mr. Madison, what you've just said is one of the most insanely idiotic things I have ever heard. At no point in your rambling, incoherent response were you even close to anything that could be considered a rational thought. Everyone in this room is now dumber for having listened to it. I award you no points, and may God have mercy on your soul.
Im kidding, Im kidding. Could not resist though.
Im kidding, Im kidding. Could not resist though.
#56
05-24-2008, 05:35 PM
Terminator,
I don't know much about the physics of ceramic brakes. I can only tell you this. I drove my 997s for 3 years with the red brakes. I swore that I would not spend the extra 8500 for the ceramics. Then I test drove a 997TT with ceramics. I was actually sold on the breaks!!! It was so much more responsive. I could accelerate and I had no doubts that I could stop that car in no time! I really felt this way and I could tell the difference driving my 997s back home. Do you know how these breaks rate on stopping distances? If you have not driven a car (preferably a 997s) with ceramics, you have to try them.
Are you sure the extra hundred+ HP was not the cause?
I don't know much about the physics of ceramic brakes. I can only tell you this. I drove my 997s for 3 years with the red brakes. I swore that I would not spend the extra 8500 for the ceramics. Then I test drove a 997TT with ceramics. I was actually sold on the breaks!!! It was so much more responsive. I could accelerate and I had no doubts that I could stop that car in no time! I really felt this way and I could tell the difference driving my 997s back home. Do you know how these breaks rate on stopping distances? If you have not driven a car (preferably a 997s) with ceramics, you have to try them.
Are you sure the extra hundred+ HP was not the cause?
#57
05-24-2008, 05:42 PM
Further on the question of PCCBs vs not, I took a trip down memory lane with my college physics book today and did some energy balance calculations based on the following assumptions.
The kinetic energy of 4 steel discs at a selected speed minus the kinetic energy of 4 ceramic discs at the same speed gives the incremental kinetic energy that must be supplied by the engine to reach the selected speed with the heavier steel discs. The incremental kinetic energy divided by the time required to reach the selected speed determines the average incremental HP required to reach that speed with steel discs (energy change per unit time = power). For simplicity, it is assumed that sufficient power is available to reach the selected speed in the same elapsed time with either type of disc.
So keep that in mind for the moment. The incremental HP required with steel discs vs. ceramic discs to get to some selected speed also depends on the time interval taken to get to that selected speed.
Calculation Basis
Weight of 1 steel disc: 11 kg
Diameter of steel disc: 350mm
Weight of 1 ceramic disc (front): 6 kg
Diameter of ceramic disc (front) 380mm
Weight of 1 ceramic disc (rear) 5.5 kg
Diameter of ceramic disc (rear) 350mm
All other unsprung component weights assumed identical (as for the rest of the car).
The kinetic energy of each disc consists of translational energy (forward motion) plus rotational energy (spinning motion).
Translational kinetic energy of the disc = ½mv<SUP>2</SUP> (m = mass of disc, v = forward velocity).
Rotational kinetic energy of the disc = ½Iω<SUP>2 </SUP>(I = moment of inertia, ω = angular velocity)
Moment of Inertia for disc = ½mr<SUP>2 </SUP>(m = mass of disc, r = radius of disc)
Since I needed to calculate the tire (rotor) rpm, I needed the overall tire diameter. I used a wheel diameter of 19 inches and added 2 x times the sidewall height based on the stock tire size. Tire diameter gives me tire circumference (pi x d). From forward speed and tire circumference, I calculated the rotor rpm. From rotor rpm, I calculated angular velocity.
Results
Case 1: 60 mph in 3.4 seconds Incremental power = 3.5 HP
Case 2: 100 mph in 7.9 seconds Incremental power = 4.2 HP
Case 3: 60 mph in 10 seconds Incremental power = 1.2 HP
Case 4: 100 mph in 20 seconds Incremental power = 1.7 HP
So there is a small benefit in HP consumption with ceramic discs and the benefit is highest for the maximum acceleration cases. For cases with less than maximum acceleration, the HP advantage becomes smaller which is what would be expected.
Since torque is the change in angular momentum per unit time, a steel disc requires double the torque of a ceramic disc (of the same diameter) to spin it up to the same speed in the same time interval. To put the torque value into perspective, for a single steel disc (front) the torque required to spin it up to 60 mph equivalent rotational speed in 3.4 seconds is about 3 ft-lbf (total available max torque is 460 ft-lbf without overboost on a stock TT).
Also, the rule of thumb of 10 lbs weight savings = 1HP looks about right, at least for small incremental weight savings. A weight savings of 21 kg (46 lbs) for 4 ceramic discs gives a HP advantage of around 4 HP (see Cases 1 and 2 above).
Somebody let me know if all this sounds reasonable. If anybody is interested, I have all this on an Excel spreadsheet.
My head really hurts now and I'm going to stop. I think I pulled a muscle in my brain.
The kinetic energy of 4 steel discs at a selected speed minus the kinetic energy of 4 ceramic discs at the same speed gives the incremental kinetic energy that must be supplied by the engine to reach the selected speed with the heavier steel discs. The incremental kinetic energy divided by the time required to reach the selected speed determines the average incremental HP required to reach that speed with steel discs (energy change per unit time = power). For simplicity, it is assumed that sufficient power is available to reach the selected speed in the same elapsed time with either type of disc.
So keep that in mind for the moment. The incremental HP required with steel discs vs. ceramic discs to get to some selected speed also depends on the time interval taken to get to that selected speed.
Calculation Basis
Weight of 1 steel disc: 11 kg
Diameter of steel disc: 350mm
Weight of 1 ceramic disc (front): 6 kg
Diameter of ceramic disc (front) 380mm
Weight of 1 ceramic disc (rear) 5.5 kg
Diameter of ceramic disc (rear) 350mm
All other unsprung component weights assumed identical (as for the rest of the car).
The kinetic energy of each disc consists of translational energy (forward motion) plus rotational energy (spinning motion).
Translational kinetic energy of the disc = ½mv<SUP>2</SUP> (m = mass of disc, v = forward velocity).
Rotational kinetic energy of the disc = ½Iω<SUP>2 </SUP>(I = moment of inertia, ω = angular velocity)
Moment of Inertia for disc = ½mr<SUP>2 </SUP>(m = mass of disc, r = radius of disc)
Since I needed to calculate the tire (rotor) rpm, I needed the overall tire diameter. I used a wheel diameter of 19 inches and added 2 x times the sidewall height based on the stock tire size. Tire diameter gives me tire circumference (pi x d). From forward speed and tire circumference, I calculated the rotor rpm. From rotor rpm, I calculated angular velocity.
Results
Case 1: 60 mph in 3.4 seconds Incremental power = 3.5 HP
Case 2: 100 mph in 7.9 seconds Incremental power = 4.2 HP
Case 3: 60 mph in 10 seconds Incremental power = 1.2 HP
Case 4: 100 mph in 20 seconds Incremental power = 1.7 HP
So there is a small benefit in HP consumption with ceramic discs and the benefit is highest for the maximum acceleration cases. For cases with less than maximum acceleration, the HP advantage becomes smaller which is what would be expected.
Since torque is the change in angular momentum per unit time, a steel disc requires double the torque of a ceramic disc (of the same diameter) to spin it up to the same speed in the same time interval. To put the torque value into perspective, for a single steel disc (front) the torque required to spin it up to 60 mph equivalent rotational speed in 3.4 seconds is about 3 ft-lbf (total available max torque is 460 ft-lbf without overboost on a stock TT).
Also, the rule of thumb of 10 lbs weight savings = 1HP looks about right, at least for small incremental weight savings. A weight savings of 21 kg (46 lbs) for 4 ceramic discs gives a HP advantage of around 4 HP (see Cases 1 and 2 above).
Somebody let me know if all this sounds reasonable. If anybody is interested, I have all this on an Excel spreadsheet.
My head really hurts now and I'm going to stop. I think I pulled a muscle in my brain.
#58
05-24-2008, 07:46 PM
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Join Date: Apr 2008
Location: Covington, Louisiana
Posts: 166
Rep Power: 37
Terminator, you got a deal! All that ciphering made me thirsty. Next time I'm through London I'll drop you an email. I actually get through there once in a while. Am in Nigeria at the moment on business.
I had agreed with your previous post on the subject and it got me wondering. A 48hp gain did seem to good to be true just from swapping out rotors. Anyway, to me the benefit of the PCCBs is in the stopping, not the going.
I had agreed with your previous post on the subject and it got me wondering. A 48hp gain did seem to good to be true just from swapping out rotors. Anyway, to me the benefit of the PCCBs is in the stopping, not the going.
#59
05-24-2008, 10:27 PM
The pccb's are one of my favorite options on my car and worth every cent. I drove them first in Europe last fall for a week on a C4S and was amazed by how responsive they were. Now I have them on my new Turbo and LOVE them. They can stop on a dime, no break dust, look amazing, and were worth every cent. I live in Seattle where we have had lots of rain since I got my car. I believe I have a new generation of these breaks (generation 3). I really cannot notice any difference in the rain or dry conditions - they handle great in all conditions so far. You will not regret ordering these.
