Differences Between Brembo 380mm/380mm BBK and 365mm/345mm BBK

[lucid]

Originally Posted by JAJ

The Hamann front splitter has openings to the left and right of the center lower oil cooler air intake that look like they'd be perfect for brake cooling. I thought of getting one just to see if I could make it work, but then I saw one on a car and realized it wasn't for me. Still thinking about how to do it.

You might find this amusing, but I bet if we look around long enough we can use cheap plastic vacuum cleaner tubes (rigid ones). They come in all sizes and shapes, and they do have those flat adapters (not sure if we can find one large enough but I think we can.) There are plenty of screws under that part of the car holding things in place, so it would be a matter of safely screwing that stuff under the car and then using regular ducting to get the air to the axle. Then you need the backing plates though, and you'd porbably have to remove that setup after the track day. I wonder if any of the backing plates Turner is selling can be made to work?

http://www.turnermotorsport.com/html...&BackingPlates

[SenorFunkyPants]

These figures are quite interesting, the E92 M3 turns out some pretty decent figures.
All from German Sport Auto, (some of the data was taken on different days/tests) normally using Nurburgring and Kliner Hochenheim, 2D logger and same driver.

M3 E92, 245 front/265 rear,cups, 1640kg.
Single piston calipers 360/350mm rotors
100-0 cold: 34,1 m = 11,3 m/s²
100-0 warm: 34,3 m = 11,3 m/s²
200-0 warm: 133,9 m = 11,5 m/s²
22 degree outside, 28 degree tarmac
----------------------------------------------------------
Gallardo Superleggera 235 front/295 rear,Corsa r-compound, 1528kg full
of fuel.
6 piston calipers, 380/380mm rotors, carbon-ceramic
100-0 cold: 34,4 m = 11,2m/s²
100-0 warm: 33,8 m = 11,4 m/s²
200-0 warm: 149,1 m = 10,3 m/s²
20 degree outside, 24 degree tarmac
----------------------------------------------------------------------
CSL, 235 front/265 rear,Cup, 1421kg full of fuel.
Single piston calipers, 345/328mm rotors
100-0 cold: 33,0 m = 11,7m/s²
100-0 warm: 32,4 m = 11,9 m/s²
200-0 warm: 129,7 m = 11,9 m/s²
26 degree outside, 34 degree tarmac
----------------------------------------------------------------------
Ferrari 599 GTB Fiorano F1, 245 front/305 rear, Pirelli P zero street
tire, 1748kg full of fuel.
Multi piston calipers and carbon-ceramic rotors(brake kit cost 16000 Euro)
355/330mm rotors
100-0 cold: 35,5 m = 10,9 m/s²
100-0 warm: 35,6 m = 10,8 m/s²
200-0 warm: 140,4 m = 11,0 m/s²
24 degree outside, 29 degree tarmac
----------------------------------------------------------------------
Ferrari 360 Challenge Stradale
225 front/285 rear, Pirelli P Zero Corsa R-Compound,1387kg full of fuel.
BBK, 380/350mm rotors
100-0 cold: 35,1 m= 11,0 m/s²
100-0 warm: 35,4 m = 10.9 m/s²
200-0 warm: 140,3 m / 11,0 m/s²
-------------------------------------------------------
Porche Carrera GT
265 front/335 rear,Michelin Pilot Sport (N0), 1473kg full of fuel.
BBK, 380/380mm rotors
100-0 cold: 35,4 m / 10,9 m/s²
100-0 warm: 33,8 m / 11.4 m/s²
200-0 warm: 134,2 m / 11,5 m/s²
----------------------------------------------------------------------
997 GT2
235 front/325 rear,Cup tire, 1497kg full of fuel.
BBK 6piston front/4rear alu monoblock, 380/350mm ceramic-rotors
100-0 cold: 36 m = 10,7m/s²
100-0 warm: 35 m = 11 m/s²
200-0 warm: 134,2 m = 11,5 m/s²
17 degree outside, 26 degree.tarmac
-------------------------------------------------------
R8
235 front/295 rear,Pirelli P zero, 1595kg full of fuel.
BBK 8piston front/4rear, 380/356mm keramic-rotors
100-0 cold: 35,2 m = 11m/s²
100-0 warm: 33,3 m = 11,6 m/s²
200-0 warm: 130,7 m = 11,8 m/s²
20 degree outside, 25 degree.tarmac

[robc]

Dryer ducts and braking late is all you need. Multi-piston and bigger kits are completely unnecessary unless you really need those extra 2-3 seconds/lap. "Might" track the car? Why on earth would you ever upgrade the brakes? I did the dryer ducts and stopped braking 1/4 mile from turn in and I went about 26 days (track events) last year on a single set of Pagid RS19's and Motul 600 -- there is NO brake fade. This car does NOT need bigger/multi-piston brakes to outbrake almost anything. I know there are folks even faster than me (by a lot) that don't even have the add-on ducts and see no need for a BBK. I had bigger heat problems when I first got the car (and was much slower) braking LONGER before turn-in, as I got faster and started braking LATER and SHORTER, all my heat issues went away.

[lucid]

Where exactly you start braking has nothing to do with how much heat you put into the system. The only thing matters is how much kinetic energy you end up losing (and converting into heat), meaning the speed at which you start braking and the speed at which you stop braking. That is the only thing that matters, the rest is not a factor. That is the basic physics. Yes, if you slow more than you need to, you will put more heat into the rotors, but that means you are putting in slow laps. And, the stock system without cooling will eventually run into trouble with RS19s if you put in many hot laps in a row. RS19s have a fairly flat friction curve, but they do have a lower MOT than race pads, and you will reach that eventually if you pound on the brakes lap after lap.

[SenorFunkyPants]

Wouldn't braking hardest and shortest produce a benefit in that the rotor would reach a much higher temperature (than a longer softer braking period) and thus lose heat at a higher rate?

[lucid]

Originally Posted by SenorFunkyPants

Wouldn't braking hardest and shortest produce a benefit in that the rotor would reach a much higher temperature (than a longer softer braking period) and thus lose heat at a higher rate?

The surface of the rotor would indeed reach a higher temperature if you brake harder and shorter during braking (conductivity of the rotor and the time scale is a factor there). But again, convection during braking is negligable, so any heat loss consideration to the environment is not an issue during that time interval. After braking, the temperature distribution across the rotor will equalize rapidly (since conduction is occurs much more faster than convection in this case), so focusing on how much kinetic energy is being dissipated is descriptive for the purposes of this discussion.

[robc]

Sort of, in a closed system yes, kinetic energy is all that matters mass * velocity = X no matter whether it takes 5 seconds to go from v1 to v2 or 10 seconds. However -- you have significantly less time to cool if you are on the brakes too much. My statement is simply that as I got faster (better lap times), I was on the brakes for a shorter duration into each corner, and I had lower brake temps -- measured with an infrared thermometer adjusted for track temp and cool down lap times. I did say that I had lower brake temps when I was "faster" -- meaning faster lap times, so, yes, I was "putting in slow laps", that was my assertion.

Second theory: temperature created at lower pedal pressure for longer (lower pad to rotor pressure) actually creates higher temperature than higher pressure for shorter duration due to unknown (to me) properties of brake pad material.

I do not know how long it will take to reach the max temp (is that what MOT means?) of the RS19's (1382F/750C), but the hottest temp I ever was able to record was at Laguna Seca with no cool-down lap, 1000F -- and there did not seem to be any damage to the pads, I went on to use them for another 12 days or so. Longest session in normal events is 35 min, and that has not been a problem temp wise since I "learned" to drive the car.

[lucid]

Originally Posted by robc

Sort of, in a closed system yes, kinetic energy is all that matters mass * velocity = X no matter whether it takes 5 seconds to go from v1 to v2 or 10 seconds. However -- you have significantly less time to cool if you are on the brakes too much.

Convection rate <<< conduction rate, and as I said above, the heat you are transferring into the environment via convection while braking is negligable unless you really are sitting on the pedal for a much longer time than you need to, but who brakes that way anyway? You'd be going painfully slow.

Originally Posted by robc

My statement is simply that as I got faster (better lap times), I was on the brakes for a shorter duration into each corner, and I had lower brake temps -- measured with an infrared thermometer adjusted for track temp and cool down lap times. I did say that I had lower brake temps when I was "faster" -- meaning faster lap times, so, yes, I was "putting in slow laps", that was my assertion.

My point is that you were converting less kinetic energy to heat as you starting going faster (you were braking LESS and scrubbing less speed). That IS the explanation for why your temps were lower as opposed to the specific of your deceleration rate and the time you spent on the brakes (yes, they are related to how much kinetic energy you are losing).

Originally Posted by robc

Second theory: temperature created at lower pedal pressure for longer (lower pad to rotor pressure) actually creates higher temperature than higher pressure for shorter duration due to unknown (to me) properties of brake pad material.

What is the basis for this theory??? I don't see any.

Originally Posted by robc

I do not know how long it will take to reach the max temp (is that what MOT means?) of the RS19's (1382F/750C), but the hottest temp I ever was able to record was at Laguna Seca with no cool-down lap, 1000F -- and there did not seem to be any damage to the pads, I went on to use them for another 12 days or so. Longest session in normal events is 35 min, and that has not been a problem temp wise since I "learned" to drive the car.

I saw 610C at the paddoc at Watkins Glen. My Pagids held up, but wore down.

I am not familiar with West Coast tracks. How many major braking zones, and what were the top speeds you were reaching before them (corner entry speeds would help as well)?

MOT is max operating temp. The sustainable limit for the RS19s is 700C. 750C is for a very short period of time, meaning it is probably pretty close to breaking down at that point.

[robc]

Originally Posted by lucid

Convection time constant <<< conduction time constant, and as I said above, the heat you are transferring into the environment via convection while braking is negligable unless you really are sitting on the pedal for a very long time, but who brakes that way anyway? You'd be going painfully slow.

My point is that you were converting less kinetic energy to heat as you starting going faster (you were braking LESS and scrubbing less speed). That IS the explanation for why your temps were lower as opposed to the specific of your deceleration rate and the time you spent on the brakes (yes, they are related to how much kinetic energy you are losing).

The use of caps and grammar implies you are arguing with me somehow, I hope you realize you are agreeing with me, because you are.

What is the basis for this theory??? I don't see any.

Me neither. Sorry, wrong word, meant "hypothesis". A crazy one at that, agree here as well.

I am not familiar with West Coast tracks. How many major braking zones, and what were the top speeds you were reaching before them?

Laguna is known as one of the heaviest braking tracks, I hit about 135 (speedo) before turn 2, not sure of top speeds at other corners, but they are consistently quite high.

[lucid]

Originally Posted by robc

The use of caps and grammar implies you are arguing with me somehow, I hope you realize you are agreeing with me, because you are.

Caps is to emphasize. Not sure what you mean by grammar. What I don't agree with is the hypothesis you stated below. I heard it from other people as well. Doesn't make sense to me.

Originally Posted by robc

Me neither. Sorry, wrong word, meant "hypothesis". A crazy one at that, agree here as well.

Laguna is known as one of the heaviest braking tracks, I hit about 135 (speedo) before turn 2, not sure of top speeds at other corners, but they are consistently quite high.

If you try a track like the Glen where you hit 150+ before a brazing zone, which has many other hard braking zones, you will run into issues without cooling with the RS19s and the stock system, which is what I am saying. Having said that, the BBK is not the solution to that. It will simply delay the issue. We need cooling.

Anyway, I am very curious to hear more about how you implemented the cooling ducts as I am in the process of coming up with something. Please let us know.

[robc]

Sorry, re-reading again -- you are in fact stating that the additional cool down is not at all a factor in the brake temps, and it is simply that I was causing a greater speed delta into each corner with slow lap times than fast lap times. Ok, I understand that, but I still feel that time on the brakes is a factor. You think that the extra few seconds of cooling are insignificant related to the overall joules put into the rotors?

[lucid]

Originally Posted by robc

You think that the extra few seconds of cooling are insignificant related to the overall joules put into the rotors?

Yes, that is correct. The rate at which you are converting kinetic energy to heat via friction and conducting through the rotor is much much higher than the rate at which you are convecting energy to the environment. 1-2 seconds more convection will not change that. You can do the basic calculations and find out. I did this a few months ago.

[robc]

Originally Posted by lucid

Having said that, the BBK is not the solution to that. It will simply delay the issue. We need cooling.

I am glad I am not the only...person...to think this. The stock brakes STOP. Very, very, very well. Bigger diameter/more pistons *might* make it stop faster, *might* hold more energy, but, yes, the heat is still staying in the #!@#!$% wheel well.

The stoptech's seem to be the only ones which may actually help dissipate more heat, due to the rotor design, however, for much less than $6k, you can put some air in the wheel well (or suck it out), and do very well with stock brakes in non-competitive environments.

I am in fact working with a carbon fiber manufacturer to produce a part which we will be selling for a few-hundred $'s that combined with the hoses, should nearly solve this issue for most of us (again, as long as you are not racing) with stock brakes.

[robc]

Originally Posted by lucid

Yes, that is correct. The rate at which you are converting kinetic energy to heat via friction and conducting through the rotor is much much higher than the rate at which you are convecting energy to the environment. 1-2 seconds more convection will not change that. You can do the basic calculations and find out. I did this a few months ago.

As little as there is, *some* air does flow through there, how did you determine the rate of heat dissipation at the "highest speed" points of the track? (right before you start braking before each corner -- here I go with one of my crazy hypotheses again -- if you brake 2 seconds earlier into each corner, you lose cooling at the point of the greatest rate of heat dissipation)

[robc]

I really need to proofread my posts better -- I did not mean to state that cooling is completely unnecessary -- I have been ranting about the absurdity of no cooling ducts in this car since my first track day in March 2008 -- an M car -- with NO brake cooling?!?!!

My initial statement was meant to state that a BBK is not going to help you on the track (due to lack of cooling in the car), and a BBK is probably a complete waste of money, (unless you are competing).

[lucid]

Originally Posted by robc

As little as there is, *some* air does flow through there, how did you determine the rate of heat dissipation at the "highest speed" points of the track? (right before you start braking before each corner -- here I go with one of my crazy hypotheses again -- if you brake 2 seconds earlier into each corner, you lose cooling at the point of the greatest rate of heat dissipation)

I was using published data a from a brake manufacturer that designed the brake system for the Veyron. They provide convective heat transfer coefficients for different parts of the disc. I did that some time ago, and I can't remember the details, but I remember being rather liberal and the convection rate was still less than 2% of the heat creation/conduction rate. That was a rough estimate, but it is in the ball park.

[lucid]

Originally Posted by robc

I am glad I am not the only...person...to think this. The stock brakes STOP. Very, very, very well. Bigger diameter/more pistons *might* make it stop faster, *might* hold more energy, but, yes, the heat is still staying in the #!@#!$% wheel well.

The stoptech's seem to be the only ones which may actually help dissipate more heat, due to the rotor design, however, for much less than $6k, you can put some air in the wheel well (or suck it out), and do very well with stock brakes in non-competitive environments.

I am in fact working with a carbon fiber manufacturer to produce a part which we will be selling for a few-hundred $'s that combined with the hoses, should nearly solve this issue for most of us (again, as long as you are not racing) with stock brakes.

I agree. The stock brakes have impressive stopping power as long as there are no temperature issues. A BBK would most likely improve pedal feel and modulation charactersitics though, but that is just an opinion at this point.

I would be very interested in what you come up with in terms of a backing plate for the rotor that one can hook cooling hoses to. Turner currently sells such a CF part for the E46 M3. They said they are developing something for the E9X M3, but wouldn't give an ETA.

[robc]

Originally Posted by lucid

I was using published data a from a brake manufacturer that designed the brake system for the Veyron. They provide convective heat transfer coefficients for different parts of the disc. I did that some time ago, and I can't remember the details, but I remember being rather liberal and the convection rate was still less than 2% of the heat creation/conduction rate. That was a rough estimate, but it is in the ball park.

Interesting. This specific data for our car would be incredibly useful in sizing the cooling setup. Due to the fact that any solution will either "obtrude" from the standard bodywork somehow, or, steal air from the CAI or oil cooler, knowing how small of a setup is necessary would make the process of producing a useful (and safe, allowing necessary cooling of other components) setup that much more efficient.

[lucid]

Originally Posted by robc

I have been ranting about the absurdity of no cooling ducts in this car since my first track day in March 2008 -- an M car -- with NO brake cooling?!?!!

I couldn't agree more!

[lucid]

As to what a solid BBK can do at the hands of a pro driver, see James Clay's post #28 here:

http://www.m3post.com/forums/showthr...=232463&page=2

He is saying he was able to brake 25' later than stock with the PFC system.

One can debate what that would mean for an enhusiast though...

[robc]

Originally Posted by lucid

As to what a solid BBK can do at the hands of a pro driver, see James Clay's post #28 here:

http://www.m3post.com/forums/showthr...=232463&page=2

He is saying he was able to brake 25' later than stock with the PFC system.

One can debate what that would mean for an enhusiast though...

I would love to debate that.

But seriously -- and I am not trying to actually start a debate -- here is my thought process on significantly reducing braking distance:

--can you threshold brake? if yes, then what does additional braking power give you?

Question: if I can lock up my wheels X feet from turn in, how does having more braking "power" help me? Does your leg get tired so you can't brake as hard next time?

My opinion is that modulation is key -- the more consistent and the better the feedback the more reliably you can modulate to achieve same level of braking lap after lap, but, to "reduce" your braking by 25' is something I do not understand. To be able to consistently brake at the same point due to increased confidence I understand.

[lucid]

Originally Posted by robc

I would love to debate that.

But seriously -- and I am not trying to actually start a debate -- here is my thought process on significantly reducing braking distance:

--can you threshold brake? if yes, then what does additional braking power give you?

Question: if I can lock up my wheels X feet from turn in, how does having more braking "power" help me? Does your leg get tired so you can't brake as hard next time?

My opinion is that modulation is key -- the more consistent and the better the feedback the more reliably you can modulate to achieve same level of braking lap after lap, but, to "reduce" your braking by 25' is something I do not understand. To be able to consistently brake at the same point due to increased confidence I understand.

Nothing wrong with a healthy respectful debate.

Yes, if the limiting factor is the grip your tires can provide you, you can't benefit from the increased breaking torque a better system can provide you. I guess one possibility is that the stock system's ability to provide more breaking torque than your tires can deal with diminishes with prolonged use and rising temps, whereas that might not be true for a BBK. I present that as a possiblity. No data to test it.

And yes, improved ability to modulate is important. And a high quality BBK should be able to offer better modulation ability than stock or not?