Carbon Brakes - walk away or worth it?
Discussion
Whatever MrD feels to be the case must be right, irrespective of both the tests (which have been posted) and the science that explains the test results (which has been kindly dumbed down for us and set out patiently and helpfully).
It could not, for example, be the case that differences in brake feel and perceived braking do not equate to differences in actual performance, could it?!
Sometimes, MrD, you are a parody of yourself :-)
It could not, for example, be the case that differences in brake feel and perceived braking do not equate to differences in actual performance, could it?!
Sometimes, MrD, you are a parody of yourself :-)
ORD said:
Whatever MrD feels to be the case must be right, irrespective of both the tests (which have been posted) and the science that explains the test results (which has been kindly dumbed down for us and set out patiently and helpfully).
It could not, for example, be the case that differences in brake feel and perceived braking do not equate to differences in actual performance, could it?!
Sometimes, MrD, you are a parody of yourself :-)
What the 60-0 mph test lol , You can over come the tyre grip at 60mph.It could not, for example, be the case that differences in brake feel and perceived braking do not equate to differences in actual performance, could it?!
Sometimes, MrD, you are a parody of yourself :-)
The real test are in the 120mph figures, I,ll post my result do you want to take a wager ?
It's very easy to lock a front tyre on a 911 - especially on slicks - without ABS. You can always tell a rookie in a 997 cup because he is constantly locking his front tyres in the brakng zone. You do need not need carbon brakes to overcome grip generated by a slick on GT3 or GT3 Cup. Steels will do that quite well enough. What stops a road going porsche from locking early in the braking zone is abs. if you trigger abs, your braking zone will be extended whether you run steels or ceramics. The last thing that you want to do is trigger the abs in the braking zone because it's not quick.
Road going cars do not generated anywhere near the grip levels from their tyre/aero combination to benefit from ceramic retardation. LMP2/1 do but big sports cars do not. There is a benefit to GT cars in terms on servicing times on long stints during 6/12/24hour endurance racing but in terms of lap time it's very marginal.
It is very difficult to compare the relative braking efficiencies between 2 different cars as one ( a GT3 compared to a boxter for example ) may be approaching the braking zone at a much higher speed than the other and therefore may need to brake earlier in order to make the apex.
The ceramic/steel argument is an emotive one. From my perspective as a racing driver with a fair bit of experience in GT3's, in terms of race pace, the marginal improvement in performance is so small as to be negligable. Especially when compared to the increase in running budgets. Porsche will have you believe that the improvement of Supercup times over Carrera Cup is due to the ceramic brakes on the Supercup cars compared to the Steel counterpart on the Cup car. This is absolute rubbish. The times are quicker solely because the rubber laid down by the F1 cars provide far more grip to the cars. I have seen test data from a Supercup car and a Cup car driven by the same driver on the same day. The times were near identical. Porsche run them in Supercup because they need to justify their performance over the steel to their markets and the Supercup budgets are so huge that the marginal cost of ceramics are therefore easier to absorb.
Obviously there may be other practical reasons why a driver may wish to specify ceramic brakes to a road car over steels but when in terms of performance there is no discernable gain.
Road going cars do not generated anywhere near the grip levels from their tyre/aero combination to benefit from ceramic retardation. LMP2/1 do but big sports cars do not. There is a benefit to GT cars in terms on servicing times on long stints during 6/12/24hour endurance racing but in terms of lap time it's very marginal.
It is very difficult to compare the relative braking efficiencies between 2 different cars as one ( a GT3 compared to a boxter for example ) may be approaching the braking zone at a much higher speed than the other and therefore may need to brake earlier in order to make the apex.
The ceramic/steel argument is an emotive one. From my perspective as a racing driver with a fair bit of experience in GT3's, in terms of race pace, the marginal improvement in performance is so small as to be negligable. Especially when compared to the increase in running budgets. Porsche will have you believe that the improvement of Supercup times over Carrera Cup is due to the ceramic brakes on the Supercup cars compared to the Steel counterpart on the Cup car. This is absolute rubbish. The times are quicker solely because the rubber laid down by the F1 cars provide far more grip to the cars. I have seen test data from a Supercup car and a Cup car driven by the same driver on the same day. The times were near identical. Porsche run them in Supercup because they need to justify their performance over the steel to their markets and the Supercup budgets are so huge that the marginal cost of ceramics are therefore easier to absorb.
Obviously there may be other practical reasons why a driver may wish to specify ceramic brakes to a road car over steels but when in terms of performance there is no discernable gain.
fioran0 said:
Its about the dT.
Q is provided by the kinetic energy, the mass and Cp are fixed. So under braking temp changes. As a result the pccb will see a larger rise in temp for the same energy. This requires more cooling to reduce this increased temp. There are various ways to address this.
But PCCB also have a critical upper temp limit since the carbon oxidises at around 750 deg making it even more important.
Did you mean to say radiative heat transfer? Its a 4th power equation (though most usually a power of 3 when calculating). There's also conductive and convective heat transfer occurring.
With larger dT, the rate of joules transferred per second as heat loss is larger but as dT reduces the rate reduces too. Once the dT is the same as steel the rates of heat loss will be the same.
Specific heat capacity is about the amount of energy required to cause a change in temp. The lower the figure, the less energy needed to cause temp to rise.
Accepting all this, there is also the issue of comparative surface area and when the carbon disc is down to the same temperature as the steel it retains far less heat energy. QED, the carbon brakes as optioned will dispose of braking heat far more efficiently than the steel originals fitted as standard.Q is provided by the kinetic energy, the mass and Cp are fixed. So under braking temp changes. As a result the pccb will see a larger rise in temp for the same energy. This requires more cooling to reduce this increased temp. There are various ways to address this.
But PCCB also have a critical upper temp limit since the carbon oxidises at around 750 deg making it even more important.
Did you mean to say radiative heat transfer? Its a 4th power equation (though most usually a power of 3 when calculating). There's also conductive and convective heat transfer occurring.
With larger dT, the rate of joules transferred per second as heat loss is larger but as dT reduces the rate reduces too. Once the dT is the same as steel the rates of heat loss will be the same.
Specific heat capacity is about the amount of energy required to cause a change in temp. The lower the figure, the less energy needed to cause temp to rise.
Edited by fioran0 on Friday 23 May 00:33
Given that carbon disc wear with sensible use is now good, and given all the other advantages that have been "worn out" ... for many people the Carbon Brakes offer a tangible advantage.
I have lost more value of steel discs to wear and corrosion (different cars !) than I have value of Carbon discs in an equivalent driving mileage.
More statistics and misleading facts !!
But, I like them ...
Had a few minutes to sort through some stuff to add into this thread. Some test sheets for different Porsches. Variety of transmissions, weights, tyres, brake systems (PCCB and non PCCB) and models. There are track variations (surface differences) and temp variations. Braking distances are given for multiple 70-0mpg stops.
70mph stops are pointless imo, that is all about tyre grip. and how good the driver is at Threshold braking.
get ABS cutting in and the distance goes up 20 feet.
you need to be testing 120mph in the real world, to test braking performance.
Just tried my R and got 154 feet but was not a great stop on a rough road.
means nothing at 70mph imo.
get ABS cutting in and the distance goes up 20 feet.
you need to be testing 120mph in the real world, to test braking performance.
Just tried my R and got 154 feet but was not a great stop on a rough road.
means nothing at 70mph imo.
Edited by mrdemon on Thursday 5th June 15:42
I don't have any disparaging or sarcastic comments to make I am afraid.
Just to say, I would love to spec a car with pccb but feel it's too much of an outlay for my needs, but would love to get a used car with them as it seems to be a very quickly depreciating option.
Even just from the fact they are six pots not four pots and a bigger disc is good in my book.
Just to say, I would love to spec a car with pccb but feel it's too much of an outlay for my needs, but would love to get a used car with them as it seems to be a very quickly depreciating option.
Even just from the fact they are six pots not four pots and a bigger disc is good in my book.
I just thought I'd add my experience to this. I'm a very keen driver and do many track days, I'm pretty competitive and tend to get decent lap times too for the machinery I'm in.
Any way, I have pccb on my '08 cayman s and love them, when looking to buy my car I drove 2x cayman s' with steel brakes and the pccb where much better.
That said, I agree the pad choice is much better on steels.
Pccb are very expensive yes, but a lot of people seem to overlook the fact that uprated two piece discs are damned expensive also.
I fitted a stoptech bbk to my previous car and it completely solved the braking issues I had (wear rate, not braking power) but again this was also an expensive option.
The fact that the standard cayman s brakes are 319x28mm front and 299x24mm alone warrants the pccb option. As they are 350x34 front and 350x28. Even if the discs where to fail you are still left with a bigger braking system when replaced with steel discs and that will allow for better heat absorption due to the size, and much better wear rates.
Any way, I have pccb on my '08 cayman s and love them, when looking to buy my car I drove 2x cayman s' with steel brakes and the pccb where much better.
That said, I agree the pad choice is much better on steels.
Pccb are very expensive yes, but a lot of people seem to overlook the fact that uprated two piece discs are damned expensive also.
I fitted a stoptech bbk to my previous car and it completely solved the braking issues I had (wear rate, not braking power) but again this was also an expensive option.
The fact that the standard cayman s brakes are 319x28mm front and 299x24mm alone warrants the pccb option. As they are 350x34 front and 350x28. Even if the discs where to fail you are still left with a bigger braking system when replaced with steel discs and that will allow for better heat absorption due to the size, and much better wear rates.
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