theCARhack

First thing we’re all familiar with is the brake pedal. We all know that you push the pedal and the car slows down. What is happening (behind the dashboard) is the pedal is attached to an arm that has leverage about a fulcrum pushing on a rod connected to a piston. This piston is located in the master cylinder and the cylinder is filled with brake fluid and pressurized by the piston. The pressure is then split between the front and rear brake lines in what is essentially a pressure regulator. The reason for this is more pressure is sent to the front than the rear because of the weight of the car – more accurately the weight transfer. As a car slows down, weight is transferred to the front tires giving them more grip than the rear. This increased grip allows a higher percentage of the brake force to be generated by the front tires compared to the rear.

The brake fluid flows through a tube (or brake line) under pressure actuating a piston that is located inside the brake caliper. When there is line pressure this piston pushes on the brake pads which in turn push on the brake disk (or rotor). When the pads contact the disk it generates friction between the two surfaces causing the disk to slow down. The byproduct of this friction is heat, sometimes extreme. To dissipate the heat there are vents in the rotors and they look like little webs between the two rotor surfaces. These vents essentially pump air through the webs from the inside out when rotating. Race cars often put flexible air ducts from an inlet on the front of the car to the rotor giving a better supply of cool air. Due to the high temperatures these components are subjected to a good boil resistant brake fluid is necessary. This fluid should be bled or changed regularly-- more frequently with aggressive use.

Rotors

Rotors have been developed significantly through racing and the technology is readily available for the street. To better deal with the heat generated by repeated use, rotors have taken on a two piece construction. The rotor is separate from the center portion commonly known as the hat which connects the rotor to the hub and wheel. The hat is usually made from aluminum while the rotor is often cast iron. These two components are attached together with small bolts. The main benefit of having a two piece (or floating) rotor is that it allows the rotor to expand and contract with the change in temperature which significantly reduces warping tendencies of solid one piece rotors. The attachment holes that the bolts go through are slightly oval in shape and this allows the rotor grow in diameter. These attachments also give the rotor the ability to move slightly in and out from a cross car perspective. Springs are sometime used to keep the rotor from moving too freely which can generate noise.

Holes and Grooves

Another detail of rotors is the holes (a.k.a. cross drilled) or grooves (a.k.a. slotted) in the friction surface itself. Cross drilled rotor holes go all the way through the rotor while a slotted rotor has grooves cut partially into the surface in a variety of different patterns. Cross drilled and slotted rotors are effective because these features allow the gasses generated to escape from between the pad and rotor. Gas generation is normal when the pad material is ground off against the rotor. The problem with not allowing these gasses an escape route is they will actually cause the pads to float slightly on the rotor not unlike an air hockey puck. These features also help a similar case where if the brake system is wet it gives the water a place to go allowing optimal performance of the brake system.

Calipers

Moving on to brake calipers there are two basic kinds - floating and fixed. Floating calipers go with fixed rotors while fixed calipers go with floating rotors. A floating caliper typically has just one large piston located on the inboard side of the caliper and a structure that wraps around the rotor allowing it to retain two pads. This style of caliper is floating because it is able to move in a cross car direction with the application of the brakes and also to adjust as the pads wear down. It is strong, effective and less expensive to produce than a fixed caliper.

The fixed caliper’s body does not move just its piston move to push the pads to the rotor. The designs do vary, but the most common type is a 4 piston set up whereby two pairs of horizontally opposed pistons provide the pushing force of the pads to the rotor. These caliper structures are designed to be strong to withstand high pressure, better dissipate heat and high overall brake performance. Another term you might hear is “monoblock” and this means the caliper is machined from a solid billet of aluminum. This is beneficial because it is the best combination of weight and strength while avoiding the seam whereby two halves are bolted together as with most fixed calipers. Race cars often use monoblocks, but they are more expensive due to the added machining time. The pistons are also important in how they are sized for the weight of the car and master cylinder.

Pads

Pads are an important part of the equation too. They have a significant impact on the systems overall performance because they can be made from a number of different compounds all designed to give different levels of friction and longevity. Pads for a street car would likely target low noise, good friction properties and longevity. On the other hand a track pad may have no noise considerations, high friction properties and depending on the length of the race, longevity may be a few hours. Brake pad dust is another thing that street pads try and minimize, but we’ve all cleaned wheels to find out it doesn’t last as long as we would like.

Lines

One last thing I want to bring up is brake lines. Not the main lines running from the master cylinder to each corner of your car, but the reinforced rubber lines that run the short distance from where the steel line terminates to the caliper fluid inlet. Due to suspension movement these cannot be hard lines. One popular upgrade for those going to the track is the replacement of the rubber lines with braided stainless steel lines. These are stronger; reducing the expansion of the line as pressure goes up in the system. This stronger line improves pedal modulation and feel.