Do you need that big brake kit? When should you bleed your brakes? What's the difference between fixed and sliding calipers? All this and more, answered.
By Jack Baruth, May 21, 2018
Somebody once wrote, "you become a folk guitarist to meet girls, but you end up talking to other middle-aged men about your fingernails." By the same token, I became a track rat to experience high speeds, but I've ended up talking to other middle-aged men about brake compounds. It always surprises me what my friends and fellow drivers don't know about brakes, brake pads, brake fluid, and other topics along these lines. Sometimes it surprises me what I don't know.
So let's go over some of the basics that you won't hear from your friends or the average enthusiast-car forum. If you read through all of this and you still have questions, ask them in the comment section at the bottom of this page, and I'll try to address them in a future article. On your marks, set, go!
How do disc brakes slow me down?
When you press your brake pedal, it moves a hydraulic piston inside a cylinder. This piston is typically narrow (small bore) and it covers a long distance (long stroke), pushing fluid out to the four corners of the car. At each wheel, there is a wide but shallow piston–or several pistons–squeezing the brake pads against a spinning disc that is mounted to the wheel hub or axle. The friction from the contact of brake pads against the brake disc slows the disc down, generating heat in the process.
How can a person pushing a brake pedal have enough strength to stop a car?
Originally, this was done with leverage. The different diameters of the brake master cylinder and the four brake pistons decrease the amount of distance that the brake pads travel while increasing the force. You push the brake pedal three or four inches; the brake pads move maybe a quarter of an inch or less, but with much greater force. Here's a great explanation of the basics of hydraulic systems and how they change motion in to force.
Modern cars have power brakes. Older systems used the vacuum from the running engine to help "boost" the driver's foot force. Many newer systems have a separate electrical pump that can generate its own brake pressure with or without your help.
How do anti-lock brakes work?
A computer compares the speed of all four wheels as the brakes are being applied. If any one wheel is slowing down faster than the rest, the computer operates an electro-hydraulic valve to "pump" the brakes on that individual wheels.
What is "threshold braking"?
It's when you use the maximum brake pressure that will slow the car without locking the wheels (in a car without ABS) or engaging the ABS (in an equipped car).
What stops me faster: Threshold braking or ABS?
If you are absolutely perfect at threshold braking, it works better than ABS. The vast majority of track rats and club racers are not perfect, so don't be too self-critical if ABS kicks in for you. In race classes where ABS is permitted, it is a major advantage
Nearly every car has brakes strong enough to activate the ABS and exceed the grip of the tires. Why do some cars have bigger brakes than others?
It's a matter of heat resistance. Larger brakes resist heat better. On the street, this is rarely an issue unless you're descending a long hill. On the track, we use the brakes hard, often several times a minute, building up heat that can't easily be shed. Which leads to fade.
Why are my brakes fading on track?
Because you're using them! Brakes heat up even in normal street use. If they can't cool off before the next time they're engaged, they'll heat up more. At some point, if the heat from the brake calipers continues to climb, it will boil the brake fluid in the pistons, causing air bubbles to develop in the fluid. If you've ever filled up balloons with water and air, you know that fluid does not compress but gases do. When your brake lines contain air bubbles in the fluid, that air gets "squished" when you hit the brake pedal, absorbing the movement of the fluid like a spring–and the brake pistons won't move until the air bubbles stop squishing, usually at very high pressure.
The fix for this? Use a high-temperature brake fluid with a 600-degree or higher boiling point.
The bad news? Racing brake fluid is limited-life stuff. If you don't flush it at least once a year, it will start breaking down, at which point it performs worse than regular street fluid.
I boiled my brakes in the last session, but they got better between sessions. Now I'm back on track and my pedal is on the floor again! What's going on?
When boiled brake fluid returns to normal temperature, it can absorb some of the air bubbles and regain normal operation. But once it's been boiled, the chemicals in the fluid have been altered, making it even more likely to boil again. The only solution: Bleeding the brakes.
Why, how, and when do you bleed brakes?
Bleeding the brakes ejects the heat-damaged brake fluid as well as the bubbles that developed during extremely high-temperature braking. The "how" depends on your particular car. The "when" is simple: Once a year at the minimum, plus every time the pedal gets soft on track.
What makes a "track" brake pad different from a street pad?
Every brake pad works best at a particular temperature. Street brake pads are optimized for use in normal driving conditions. They have to work at below-freezing ambient temperatures and they have to work in Death Valley. But they don't handle the heat of constant on-track application very well. For that, you'll need high-temperature brake pads. They work better on track, but they can result in iffy, frightening stops when they're cold, and street driving probably won't bring them up to operating temperature. They also make a lot of noise. The best thing to do is to change pads at the track.
If I have high-temperature fluid and the right pads, do I really need bigger brakes?
Often, the answer is no. Both of my race cars–a Plymouth Neon and a Mazda Miata MX-5 Cup car–use the stock factory calipers and discs, front and rear. Changing the pads to Hawk's DTC compound and changing the fluid to Motul 600 is enough to make them race-ready. On heavier, more powerful cars, you might need to do more than that.
Fixed vs. sliding calipers: What's the difference?
Once upon a time, most disc brake calipers had one piston on each side of the disc. The original disc brakes on jet airliner landing gear worked like this; so did the brakes on the Porsche 917. Then somebody figured out how to make a single piston squeeze both sides of the disc via a sliding sleeve mechanism. This was cheaper and easier to fix, so it became almost universal on street cars. In the past 20 years, "fixed" calipers with pistons on both sides have become popular again, often with as many as four pistons on each side.
The advantages of fixed calipers: Easy pad changes, a stiffer pedal, more heat resistance.
The advantages of sliding calipers: Much cheaper to maintain, better at shedding heat between brake applications.
Why do some cars have almost equal size front and rear brakes, while others have big brakes up front and tiny calipers in back?
Sometimes it's because of weight distribution. With a front-drive, transverse-engine car, there's almost no weight in back, so the calipers don't have much of a job to do. Mid-engined and rear-engined cars need a more balanced arrangement.
It's become common in recent years for new cars to have a "performance brake" option that combines name-brand fixed calipers up front with plain-jane sliders in back. That's usually done for cost reasons, and it's a shame.
Should I upgrade to an aftermarket "big brake kit"?
Not unless you are experiencing significant fade using proper race-compound pads and high-temp fluid in the factory system. Changing to a big brake kit can increase wear and tear on the car. It can confuse the ABS and the stability control. Last but not least, the kind of money you would spend on a brake kit could pay for a whole season of track days.
Should I buy the factory big brake option on a new car, if I have the chance?
If you have any plans to track the car, absolutely. All the issues with aftermarket big brake kits that I mentioned above will have been solved by the factory engineers.
Should I buy the carbon-ceramic brakes if they're an option on my new car?
I'm personally wary of the cost of carbon-brake consumables. Make sure you understand how much it will cost to swap pads and rotors each time–and make sure you understand how often it will happen. Even financially successful track rats will often find the cost of a full carbon brake "refresh" to be a bit daunting. I like to stick with the steel brakes and change the parts out more often, but that's just me.
What else can I do to increase my brake performance?
On many cars, you can pull your fog lights or cut holes in your lower valance, then run some tubing from those holes to your front calipers for increased airflow across the brakes. This can cool the brakes off faster and reduce fluid boiling.
Since the stability control system uses your brakes, turning it off can reduce your brake temperatures, particularly in the rear calipers. However, that often causes a whole new set of problems. Proceed with caution.
Last but not least, get in the habit of proper racetrack brake application. Using your brakes correctly will reduce the rate at which they heat up, thus allowing you to get more stopping power from the same setup.
What if, even after considering all of the above, my brakes are still terrible?
If you've had a qualified mechanic look at them and tell you, "that's all there is," you can always change your driving style to suit your brakes. I've had plenty of very happy days on track in bone-stock rental sedans like Camrys and Malibus. In those cars, I use the brakes sparingly and I come off the throttle for a while before each brake application. It's kind of like the way people used to race in the drum-brake era, where a single hard use would ruin your brakes for a few laps, if not the whole race. You can still have a lot of fun without threshold-braking up to every single turn-in point all day. It's better than not being on track at all.
Eventually, however, you'll get tired of that and start thinking about your next brake setup, or your next car. When that happens, and you find yourself sitting in the paddock talking to a bunch of middle-aged dudes about "pad compound" and "caliper clearance"... well, you can't say I didn't warn you!