Brake Overheating, Brake System Improvements

by Rob Schermerhorn on July 1, 2011

Energy Conservation: Brake System Preparation/ Best Practices

Preparation is the key to a successful day at our performance drivers school; the brake system is priority two (#1 is tires) on your pre-event list. Proper maintenance is not an expensive proposition, just plan ahead.

Here’s the checklist:

  • Brake pad thickness, not more than 50% worn
  • Brake fluid fresh, not more than three months old

Looks pretty simple and it is. If you’re a novice the above inspections and required maintenance carried out by a qualified technician is all you need to help you have a fun-filled first event.

Intermediate level performance drivers: read on…

Here’s the recipe: MIX the following on a racetrack

  • 4,000 pounds
  • 400 horsepower
  • Five deceleration zones
  • 120 mph – 45 mph in four seconds
  • Three mile long lap
  • 20 minute session length

Five times per lap, six laps per session: THAT’S A LOT OF ENERGY!

Some eye-opening numbers (with help from my race engineer friends at Precision AutoResearch):

At a deceleration rate of about 0.90G (which virtually any modern unmodified car can produce) this equates to over 2,300 BTU of energy; unit conversion to put this in perspective:

825 HORSEPOWER PER BRAKE ZONE!

Wow, bet that number gets your attention; now perhaps it’s easier to understand how intermediate level performance drivers—using their brakes harder now with more experience—suffer brake system issues with some frequency.

1100°F+ rotors... smokin!

This amount of kinetic energy must first be absorbed by your cast iron (or carbon ceramic if you’re an exotic car owner) front brake rotors (70% of braking energy is managed by front brakes), raising their temperature during the first stop from ambient to about 800°F, by the second lap you’re flirting with 1,000°F, two laps later sparks of molten iron are tossed onto the inside of your wheels (and subsequent scrubbing of embedded particles from the wheel paint). The kinetic energy is transformed to heat; but the unmodified rotor cannot shed the heat quickly enough and some of that heat is transferred through the brake pad (ostensibly an insulator) to caliper pistons, piston seals and brake fluid, raising fluid temperature to over 500°F, beyond the dry boiling point of generic brake fluid.

Enter Señior Spongy Brake Pedal!

What can you do to prevent, reduce severity or delay this from happening?

  1. Fresh high-quality fluid with a dry boiling point greater than 500°F
  2. Thick brake pads in a compound formulated to perform at 1,000°F (not combo street-track pad formulations)
  3. Heat insulating titanium brake pad shims (titanium is a thermal insulator)
  4. Duct air directly to the center of vented front brake rotors
  5. Add low volume flow water aspirator to brake air duct

Okay, so items 1 – 3 are easy for anyone to perform and add to their preparation list, not so easy with 4 and 5. All of this is exactly what I’ve done in my former career as race engineer; it’s the only way a production-based or tube-frame race car can survive more than just a few laps. Brake air ducting kits are becoming more common as manufacturers and the aftermarket realize their customers participate in performance driving events.

We’ll have product reviews and evaluations in the future; in the meantime bookmark in your browser or subscribe via RSS feed. Feel free to link to this post in forums.

Questions, comments please!

{ 3 comments… read them below or add one }

Kent Beecher December 13, 2011 at 5:51 am

There are a number of air ducting add-ons used by C5 Corvette owners. The least expensive one I’ve found is to buy two C6 Z06 under bumper to front wheel-well ducts and combine them with the existing C5 ducts to get air back to between the A-arms. Then, it’s relatively easy to add some high-temp 2 1/2 inch hose tie wrapped to the upper A-arm to get the air directly to the rotor. Even with Motul 600, fresh pads and almost new drilled and vented Baer rotors, I suffered significant brake overheating at Road America so I’ve added the above ducting for the coming season. Part of my problem may have been that I didn’t take an “easy” lap after a couple of hot laps to let things cool down – was having too much fun!!

Reply

Rob Schermerhorn December 13, 2011 at 6:22 am

Hi Kent, great solution! Adding ducting (properly) by designing your own is a lot of work but worth the effort. I agree, Road America can be tough on brakes (three long straights followed by slow corners three times per lap, so every minute your brakes absorb more than 800hp! That’s a lot of energy… see you next season!

Reply

Rick Schoonover December 13, 2011 at 6:53 am

GREAT article Rob! Do you know of anyone that has a good brake duct kit for my E90 BMW 335i? As you know I’m already running track specific (Performance Friction) pads, high temp fluid, and brake my “company car” harder than anyone has the right to brake a car that the owner of their company technically owns!!

Thanks, Rick

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