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      01-30-2011, 05:14 PM   #27
lucid
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Drives: E30 M3; Expedition
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Quote:
Originally Posted by jragan View Post
I completely disagree with this as a blanket statement. As new drivers get better, they do in fact get faster by using the brakes less. It's a fact that new-to-tracking drivers do overuse the brakes because they have neither the confidence nor the ability to brake later and carry more speed through the turn so they brake early and long thus going slower and over-using the brakes. Not to mention, newer drivers leave DSC on which is also going to overuse and overwork the brakes thus resulting in slower average speeds and a potentially failed braking system.

As drivers get better, they do use use the brakes less and less until they reach the terminal velocity that their car/equipment is able to sustain through a curve. You then increase the car's ability to handle additional speed around the curve via suspension modifications, weight-loss, etc so you can then brake even less and maintain even more speed through. Then you rinse, repeat, and do the process all over again until you reach the maximum capability you and your current equipment can achieve...and then you buy a lighter, lower, higher-horsepower car.
The basic physics behind all this has to do with the conservation of energy principle. First, define what using the brakes "less" means. What does it mean really? What does it mean to carry more or less speed through a corner and how is that related to using the brakes more or less?

So, a novice driver is more likely to overheat their brakes because he/she used "more" brakes compared to an advanced driver? Is that what you are saying? If it is, that's pretty much false.

The only way to objectively quantify what it means to "use" brakes is to consider how much kinetic energy is being converted to heat during braking, which is why your car slows down.

A novice driver will convert less kinetic energy to heat during braking in general, and therefore will use the brakes less. That's because he/she will aproach the braking zone at lower speeds (despite the fact he/she will exit at lower speeds). Note that kinetic energy is proportional to the square of the velocity.

Total energy converted to heat during the braking event = 0.5*mass_vehicle*(v_initial^2-v_final^2)

where

v_initial is the velocity when you apply the brakes
v_final is the velocity when you release the brakes

To think through this, let's take a braking zone before a corner where you normally do a 200kph --> 80kph. If you were to corner faster and exit that zone at 110kph instead, you wouldn't be braking less because since you are cornering faster you must now be approaching that zone at a higher straighaway speed, say 220kph (a guess; this would get very complicated if we got into drag losses etc). If you do the math on kinetic energy change for those 2 scenarios, you'll see that the faster scenario will result in more kinetic energy loss (as heat), so you used more brakes (about 8% more actually according to my quick calculations; for a 215-->110 scenario, it is ~2% more).

This is simply why, at any given trackday, in similar cars, almost none of the novice drivers overheat their brakes whereas some of the faster and more advanced drivers might.

If this wasn't the case, as people got faster, their demands on the brake system would decrease and not increase, and they wouldn't have to shell out big money to upgrade their brakes. Club race cars could run on completely stock systems, etc.

Of course, there is another dimension to this, which has to do with how much heat the rotors are transferring into the enviroment, and the faster you go on the straights, the more heat your transfer out, but that doesn't seem to be an overwhelming factor (especially for cars that do not have direct forced cooling) since if it was, again, faster drivers would not need to upgrade their brakes and racecars could run on stock system, etc.
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Last edited by lucid; 01-30-2011 at 05:59 PM..
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