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      01-31-2011, 12:35 PM   #30
The HACK
Midlife Crises Racing Silent but Deadly Class
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Drives: 2006 MZ4C, 2021 Tesla Model 3
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Lucid is 100% correct. The difference here, is some of you are talking about "learning" the process to go fast, but Lucid is talking about if you're already near the capabilities of your car, i.e. if you're good enough to consistently lap at a very high speed.

What I've found, is if you find that the "less" you brake the faster you go, you've simply not found the proper braking point/threshold on a consistent enough basis. Meaning you're over-braking for most of the brake zones and giving up unnecessary speed through the turns. So if you're going slower at the beginning of the turn, you'll be going slower through the middle of the turn and you will in turn be going slower by the end of the straight. The end result is there won't be enough cooling available in the slower section to dissipate heat. It's easy to see how a beginner to intermediate driver can potentially be braking too much to overwhelm a brake system.

But, the ultimate physics equation does not change. The faster you go, the more heat you will generate in the brake system. Some of you, if not most, will eventually get fast enough to experience this. So the question here is, how exactly do you alleviate the additional heat generated by faster laps? There are two ways to solve this. One is to upgrade the equipment. The other is by extending your braking zone, start your braking early and do the majority of your braking early in the braking zone to allow your system a longer period of time to cool down. The key in the 2nd method, is you MUST only do the same amount of braking but do it early enough so you can carry the same speed through the turns.

So what's the difference between the two methods? Method 2 is slower. Meaning you're potentially giving up .1-.2 second per braking zone depending on how "weak" your braking system is. On a complicated track this can be as much as a second per lap slower. For time-trial and racers, that is a freakin' eternity and the difference between podium and coming in LAST. So they'll go ahead and choose option number 1 by upgrading their system to a point where they can no longer overwhelm their brakes no matter how long and how fast they drive. And that's why you'll also see racers and time-trial dudes often pick up a second or two on brake upgrades ALONE.

The only point I will disagree with Lucid on, is the way temperature is measured and when/how it's measured as compared to the system's capacity. It is true that the boiling/flash point of typical DOT 4 fluid is around 400º F, and if you don't do a cool-down lap and come in and measure the rotor temp, you'll likely see anywhere between 500º F to 1,000º F depending on how hard you're pushing and where the pit is located. It doesn't necessarily mean that the brake system is being overwhelmed.

Now, if brake fluid boil at 400-600º F, how can a system that measures up to 1,000º F be okay? Well, it takes a while to boil the fluid. The brake rotors may be at 600º F, but the fluid will take a while to reach that temp, if the rotor continues to radiate that 600º F then eventually the fluid will boil and the system will be compromised. However, a well designed system should allow the heat to evacuate quickly and bring that temperature down rapidly if the rotor continues to turn (if vented, thus drawing air and heat away from the system) and not allow the fluid to reach boiling temp.

Unfortunately we don't have F1 like budget to have live telemetry on brake rotor temp, but I think what most of us will find is that the rotors on typical street cars used on track will reach around 250º F on straights (pulling numbers out of my @ss here) and as much as 1,000º F in the braking zones. Obviously, if the heat is allowed to build up and stay with the rotors then the number will climb and eventually cause a brake system failure, but I'll bet it'll be the brake PAD maximum operating temperature that'll be exceeded first.

Typically "fluid" fade problems stem from cars that does not get the opportunity to get a nice cool down lap before it comes in, or does not get a sufficient break between sessions (i.e. back to back sessions where heat is allowed to build up within the fluid). But to the rest of Lucid's point, I agree 100%...And not because O-cha disagrees.
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