From Trackpedia
Brake Systems
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All the horsepower in the world is of no use if you have no way to stop it. In this section we'll examine all of the key elements of braking systems, and discuss how they come together to provide a complete system. For hints on using the braking system, head over to the driving tips section.
Brake Fluid
Brake Lines
Calipers
Brake Pads
Brake Accessories
Once you've assembled the mechanicals and fitted them to your vehicle, you need to ensure that they are all working well on your vehicle. There are some common issues that you are bound to encounter. Below, read some suggestions on how to handle them.
Common Issues
Managing Heat
Nearly every issue brake system issue has one thing in common: Too much heat. While there are non-heat related issues, such as pad knock-back, almost everything else comes from excessive heat build up.
The two main situations that arise from heat management problems are Fade and Boiled Fluid. You can read about both of these situations on the Heat Management page.
Soft Pedal
A soft or mushy feeling pedal is typically the result of boiled brake fluid or pad knock-back.
Pad Knock-Back
The following is paraphrased from the article "A Common Racing Phenomenon"
by James Walker, Jr. of scR motorsports. The full article can be found at StopTech's website.
As the wheel, hub, and wheel bearing deflect during cornering, the rotor hat sandwiched in-between is forced to go along for the ride. Because the caliper (red in the illustration) is attached to a more rigid suspension component – the upright – the parallelism between the rotor face (gray in the illustration) and the brake pads (yellow in the illustration) is altered. In so many words, the deflection of the rotor relative to the brake pads actually forces the brake pads away from one another. This spreading action pushes the caliper pistons (blue in the illustration) back into their bores a tiny amount (horizontal green arrows in the center illustration) so that when the deflection goes away (when the cornering event is over) there is not enough springback in the piston seal to push everything back together again (green arrows in the rightmost illustration). The pads are now pushed off the rotor and will stay put until the brakes are next applied.
Pad Knock-Back In Action
Unfortunately, the next time the brakes are applied the initial travel will be used exclusively to push the pistons back up against the pads and rotor. This requires forcing fluid into the system, so the pedal feels as if it drops away toward the floor. Because this action does not build any line pressure, no torque is generated and for a brief moment the car will not slow down.
So what can you do about knockback?
There are many schools of thought on addressing knockback, each with their own pros and cons. We’ll list them here not in order of preference or recommendation, but rather to assist you, the reader, in making your own best decision.
1. Minimize wheel end deflections during cornering
While it may sound obvious, making sure that your wheel bearings are fresh and tight is the first major step toward addressing knockback. Following the wheel bearing itself, upgrading hubs and other suspension components to achieve less deflection during cornering will also serve to minimize knockback. At times, heavy-duty or race-specification components may be available for bolt-on installation. A little bit of research here can go a long way.
Most professional race teams will actually take the time to disassemble, blueprint, reassemble, and shim their wheel bearings prior to use. In addition to minimizing clearances and running gaps, the grease is upgraded as well to make sure that the bearing generates as little deflection as possible while on track.
Note that if you are experiencing knockback only after either right-hand or left-hand turns, it may be indicative of a single wheel bearing on the fritz. As right turns load left bearings and vise-versa, a little on-track analysis can sometimes lead you directly to the suspect component(s).
2. Tap-up the brakes when necessary
This practice may not sound glamorous, but you might be surprised to find how many professional road racers use this technique on a regular basis. All that is usually necessary is a one- or two-tap application of the brake pedal just moments before your braking zone arrives. It takes some practice to get used to, but like heel-toe downshifting eventually it just becomes habit. Note that if you are applying the brakes hard enough to feel the car decelerate you are applying too much pressure – you only need enough pressure to seat the components, not to build torque!
3. Install active knockback springs
In some applications the best solution is to install a spring behind the caliper piston to actively push the pad against the rotor face, even when the brake pedal is not applied. While this creates a situation where the running drag of the system goes up significantly (the brake are always applied!), it can be of great help in solving otherwise terminal knockback issues. It should be noted that this is not typically an applicable solution for street-driven vehicles – it’s primarily found on track-only cars.
4. Increase master cylinder diameter and/or reduce caliper piston diameter(s)
Both of these changes will alter the hydraulic ratio of the braking system in such a way that for a given amount of deflection, the amount of fluid displaced is reduced. While this might sound like a good solution at first pass, keep in mind that the fundamental brake system characteristics will be impacted as well! Both of these changes will require the driver to apply more pedal effort for a given level of deceleration and will certainly impact the front-to-rear bias of the braking system at the same time.
Bias/Balance
Brake System Manufacturers
Reference Links
