How Do Brake Systems Work?

[FTS]

A detailed and very informative seminar session on how modern street and racing brake systems work. This Part I, and hopefully they will make Part II available as well.

We sincerely thank Apex Performance, David Murry Track Days and of course PFC and Darrick Dong, PFC Director of Motorsports for providing the information and video.

[FTS]

Few notes I took away from the video; I am paraphrasing my understanding, so draw your own conclusions after watching the video:

• Street cars sensors for ABS, yaw, wheel speed, etc. are all integrated into a single unit; whereas purpose-built professional race cars have individual systems, which allows them to adjust setting for each individual system for optimum configuration given the track and conditions
  
• Street cars have reactive ABS systems, whereas race car systems have proactive configuration options in addition to reactive algorithms
  
• Torque vectoring - for track use, disable it. ECU looks into yaw, Long and Lat g sensors and as it detects slip on the unloaded wheel (inside rear) in a corner, activates the brakes through ABS to drag that wheel to help increase traction and reduce cornering radius. It is an overuse of the brakes that is not optimal for track use.
• Drivers objective is to figure out the fastest way to get to maximum braking performance approaching/entering a corner. Slamming the brakes is not the best approach; instead initial application needs to be one of squeezing the brakes and then rapidly increasing pressure on the pedal towards maximum deceleration performance. If brakes are slammed on street-based cars, the ECU thinks an accident is imminent and panic algorithms are initiated reducing brake fluid pressure to only ~60% regardless of what the driver is doing. This, coupled with rapid unloading of the rear wheels, results in what is known as 'ice mode.' Best way to avoid it is to initially squeeze the brakes and then rapidly increase pedal pressure and avoid ABS intervening.
  
• For 997 cars, ones possible approach is to run less aggressive pads compare to the rears.
  
• Modern ABS systems have a sampling rate of about 1 every 5 ms, which quite rapid and has become more difficult to detect its engagement, especially on rough surfaces.
  
• Two-piece brake rotors allow proportional growth of the rotor outward evenly as heat builds up, which gives the driver a more consistent feel and are less prone to cracking and deforming under stress compared to one-piece rotors.
  
• Bleed the brakes in a way that you can do both front and rear at the same time. When performing a complete flush out of the brake fluid, cycle out the ABS pumps as well. Bleed first the in-board valves first then out-board ones.
  
• When rebuilding or assembling calipers wet the seals in brake fluid for 2-3 hours. If a caliper has changed color towards a burnt shade, it is time to change the calipers. If aluminum calipers reach ~450-500 degF in a sustained manner, their overall performance and feel consistency will drop nearly 50%.
  
• One way to visually inspect calipers is to look for roundness of pistons are maintained, the pistons are able to freely move in and out even only with 5 psi air pressure and that seals have not cracked and are still soft to the touch.

Add your own as needed...

[bman]

That is a great video. I watched in full and will watch again.

Thank you for posting!

[FTS]

[FTS]

Here are two comparative videos on how BMW MDM (their version of stability control) works at the track. One of the drivers purposefully did not turn off this MDM thing and kept pushing on the corners, after a session one of his front brake pads were completely gone.

Look at the individual wheel brakes. On several occasions, even the brake pedal is not pressed, individual front outside brakes are applied. Also, you can see that the amount of brake pressure applied at the individual wheels are not always the same.

BMW MDM is On:

VS.

BMW MDM Off:

[FTS]

Part 2 of the Seminar: