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Message: The base brakes are astounding actually. And the real limiting factor to braking is.... (treatise)
Changed By: grant
Change Date: November 21, 2012 08:43PM
The base brakes are astounding actually. And the real limiting factor to braking is.... (treatise)
Change Date: November 21, 2012 08:43PM
The base brakes are astounding actually. And the real limiting factor to braking is.... (treatise)
heat. Specifically heat dissipation for prolonged, repeated use. Not one big stop, nro two. Lap after lap of 130--> 50 mph at threshold.
There are various ways to deal with this. For real racing, you do "all the below". For normal human beings however we can:
1. build huge heat sink capacity and surface area (dissipation area) via huge rotors and calipers
2. Accept that the brembos on there are plenty large as stopping devices, and condition the system to handle the heat rise. This means
2a. put high temp pads in there - 800 deg minimum; 1000-1200 true track; > 1200 HD race
2b. make sure the fluid does not boil. DOT3 = 401degF DOT 4 = 441 deg F DOT 5.1 = 518deg F Motul = 600deg F Castrol SF = hotter than the sun degF. All figures dry. Corollary is change it regularly so its dry.
Now, a rel racer probably wants bigger brakes than i have on my girly-man's car. He might need 17" tires so the rotors can fit within; and might also want the larger calipers to dissipate the heat and hold more fluid in the caliper cavity. But 19? 20?
let's look at some numbers.
I recently ran my 4000 lb Audi S6 avant (aka wagon) at VIR. The S6, like most audis, is a 911 in revers - lots of weight in front of the front axle. Teh rear brakes, under weight transfer, do not too much. So this is actually a good lab for what happens when you haul a Big Pig down from real fast to a whole lto less fast (say 115 --> 55 at the end of the back straight just before and during turn 14).
After a session (taking it overall pretty easy), and after a cool-down lap, and on a cool day ( and of course a cool driver), the front rotors were 560 degF. That's pretty hot - indicating they were what - 800+ at peak? More?
But the calipers were just under 300 deg. So that indicates that the rotor heat is the most critical - and can be dealt with by pads and rotor materials (race pads and if needed composite rotors). Or just an upsize to 17" wheels - i was running 16s on my Audi at the time - clearing the huge rotors and HP2 calipers.
It also suggests that DOT4 fluid was probably sufficient. I had 600 deg ST fluid in for safety ( and would again).
Did i mention there's a cult that upgrades hot-rod Audis to *BASE* Boxster brakes?
So, are there many circumstances that require 18s, 19s or 20s on 3000 lb cars?
For street - not even remotely close. Give up.
For track - not really, although it might occasionally be expedient.
For pro racing - they dont run stock cars anyway, so STFC?
QED.
Grant
There are various ways to deal with this. For real racing, you do "all the below". For normal human beings however we can:
1. build huge heat sink capacity and surface area (dissipation area) via huge rotors and calipers
2. Accept that the brembos on there are plenty large as stopping devices, and condition the system to handle the heat rise. This means
2a. put high temp pads in there - 800 deg minimum; 1000-1200 true track; > 1200 HD race
2b. make sure the fluid does not boil. DOT3 = 401degF DOT 4 = 441 deg F DOT 5.1 = 518deg F Motul = 600deg F Castrol SF = hotter than the sun degF. All figures dry. Corollary is change it regularly so its dry.
Now, a rel racer probably wants bigger brakes than i have on my girly-man's car. He might need 17" tires so the rotors can fit within; and might also want the larger calipers to dissipate the heat and hold more fluid in the caliper cavity. But 19? 20?
let's look at some numbers.
I recently ran my 4000 lb Audi S6 avant (aka wagon) at VIR. The S6, like most audis, is a 911 in revers - lots of weight in front of the front axle. Teh rear brakes, under weight transfer, do not too much. So this is actually a good lab for what happens when you haul a Big Pig down from real fast to a whole lto less fast (say 115 --> 55 at the end of the back straight just before and during turn 14).
After a session (taking it overall pretty easy), and after a cool-down lap, and on a cool day ( and of course a cool driver), the front rotors were 560 degF. That's pretty hot - indicating they were what - 800+ at peak? More?
But the calipers were just under 300 deg. So that indicates that the rotor heat is the most critical - and can be dealt with by pads and rotor materials (race pads and if needed composite rotors). Or just an upsize to 17" wheels - i was running 16s on my Audi at the time - clearing the huge rotors and HP2 calipers.
It also suggests that DOT4 fluid was probably sufficient. I had 600 deg ST fluid in for safety ( and would again).
Did i mention there's a cult that upgrades hot-rod Audis to *BASE* Boxster brakes?
So, are there many circumstances that require 18s, 19s or 20s on 3000 lb cars?
For street - not even remotely close. Give up.
For track - not really, although it might occasionally be expedient.
For pro racing - they dont run stock cars anyway, so STFC?
QED.
Grant
Original Message
Author: grantDate: November 21, 2012 08:42PM
The base brakes are astounding actually. And the real limiting factor to braking is....
heat. Specifically heat dissipation for prolonged, repeated use. Not one big stop, nro two. Lap after lap of 130--> 50 mph at threshold.
There are various ways to deal with this. For real racing, you do "all the below". For normal human beings however we can:
1. build huge heat sink capacity and surface area (dissipation area) via huge rotors and calipers
2. Accept that the brembos on there are plenty large as stopping devices, and condition the system to handle the heat rise. This means
2a. put high temp pads in there - 800 deg minimum; 1000-1200 true track; > 1200 HD race
2b. make sure the fluid does not boil. DOT3 = 401degF DOT 4 = 441 deg F DOT 5.1 = 518deg F Motul = 600deg F Castrol SF = hotter than the sun degF. All figures dry. Corollary is change it regularly so its dry.
Now, a rel racer probably wants bigger brakes than i have on my girly-man's car. He might need 17" tires so the rotors can fit within; and might also want the larger calipers to dissipate the heat and hold more fluid in the caliper cavity. But 19? 20?
let's look at some numbers.
I recently ran my 4000 lb Audi S6 avant (aka wagon) at VIR. The S6, like most audis, is a 911 in revers - lots of weight in front of the front axle. Teh rear brakes, under weight transfer, do not too much. So this is actually a good lab for what happens when you haul a Big Pig down from real fast to a whole lto less fast (say 115 --> 55 at the end of the back straight just before and during turn 14).
After a session (taking it overall pretty easy), and after a cool-down lap, and on a cool day ( and of course a cool driver), the front rotors were 560 degF. That's pretty hot - indicating they were what - 800+ at peak? More?
But the calipers were just under 300 deg. So that indicates that the rotor heat is the most critical - and can be dealt with by pads and rotor materials (race pads and if needed composite rotors). Or just an upsize to 17" wheels - i was running 16s on my Audi at the time - clearing the huge rotors and HP2 calipers.
It also suggests that DOT4 fluid was probably sufficient. I had 600 deg ST fluid in for safety ( and would again).
Did i mention there's a cult that upgrades hot-rod Audis to *BASE* Boxster brakes?
So, are there many circumstances that require 18s, 19s or 20s on 3000 lb cars?
For street - not even remotely close. Give up.
For track - not really, although it might occasionally be expedient.
For pro racing - they dont run stock cars anyway, so STFC?
QED.
Grant
There are various ways to deal with this. For real racing, you do "all the below". For normal human beings however we can:
1. build huge heat sink capacity and surface area (dissipation area) via huge rotors and calipers
2. Accept that the brembos on there are plenty large as stopping devices, and condition the system to handle the heat rise. This means
2a. put high temp pads in there - 800 deg minimum; 1000-1200 true track; > 1200 HD race
2b. make sure the fluid does not boil. DOT3 = 401degF DOT 4 = 441 deg F DOT 5.1 = 518deg F Motul = 600deg F Castrol SF = hotter than the sun degF. All figures dry. Corollary is change it regularly so its dry.
Now, a rel racer probably wants bigger brakes than i have on my girly-man's car. He might need 17" tires so the rotors can fit within; and might also want the larger calipers to dissipate the heat and hold more fluid in the caliper cavity. But 19? 20?
let's look at some numbers.
I recently ran my 4000 lb Audi S6 avant (aka wagon) at VIR. The S6, like most audis, is a 911 in revers - lots of weight in front of the front axle. Teh rear brakes, under weight transfer, do not too much. So this is actually a good lab for what happens when you haul a Big Pig down from real fast to a whole lto less fast (say 115 --> 55 at the end of the back straight just before and during turn 14).
After a session (taking it overall pretty easy), and after a cool-down lap, and on a cool day ( and of course a cool driver), the front rotors were 560 degF. That's pretty hot - indicating they were what - 800+ at peak? More?
But the calipers were just under 300 deg. So that indicates that the rotor heat is the most critical - and can be dealt with by pads and rotor materials (race pads and if needed composite rotors). Or just an upsize to 17" wheels - i was running 16s on my Audi at the time - clearing the huge rotors and HP2 calipers.
It also suggests that DOT4 fluid was probably sufficient. I had 600 deg ST fluid in for safety ( and would again).
Did i mention there's a cult that upgrades hot-rod Audis to *BASE* Boxster brakes?
So, are there many circumstances that require 18s, 19s or 20s on 3000 lb cars?
For street - not even remotely close. Give up.
For track - not really, although it might occasionally be expedient.
For pro racing - they dont run stock cars anyway, so STFC?
QED.
Grant