How Brake Rotors Work


Most people know what a brake rotor looks like -- but they're not all the same. Which type of brake rotor is right for you?
Most people know what a brake rotor looks like -- but they're not all the same. Which type of brake rotor is right for you?
Felix Alim/iStockphoto

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Most drivers know that they need to perform a little routine maintenance to keep their vehicle in good, working condition. That may involve regularly changing the engine oil, maintaining proper tire pressure and occasionally monitoring the levels of each of the vehicle's vital fluids. Some components and systems require a little more maintenance and others require a little less. In terms of your vehicle's braking system, if you regularly check the fluid and change your brake pads, you have nothing to worry about, right?

­­­W­ell, not quite. You're forgetting about the rest of the brake part­s, including your brake rotors. Brake rotors are an import­ant component in the braking system that stops your vehicle. Brake rotors (they're also called brake discs) are what your vehicle's brake pads clamp down on to stop the wheels from spinning. Some people may be surprised to learn that the brake rotors are just as important to stopping their vehicle as the brake pads are. Like other brake parts, there are several different types of brake rotors available. We'll take a look at a variety of them throughout this article -- pointing out the strong points and drawbacks of each along the way.­

­Keep reading to learn more about the many different types of brake rotors. You may even be able to determine which are best suited for your car or truck, and how you can maintain them.

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Drilled Brake Rotors

A lot of high-performance brake rotors are drilled, like these rotors, on the Audi R8.
A lot of high-performance brake rotors are drilled, like these rotors, on the Audi R8.
MICHAEL LATZ/AFP/Getty Images

There are two major types of high-performance brake rotors -- drilled and slotted. We'll discuss the drilled rotors here and move on to the slotted rotors on the next page. Drilled brake rotors, as the name implies, have holes drilled in them. Having a holes drilled into any of your brake parts may seem counterintuitive, especially the brake rotors -- after all, a rotor full of holes means that there's less surface area for the brake pads to grab and stop the car -- but there are a few reasons drilled rotors make sense. 

The first is heat. When the brake pad grabs the rotor, it creates friction, which creates heat. If that heat can't escape, it leads to brake fade, which reduces the brakes' stopping power. The second reason is gas build up. This actually isn't much of a problem any more; however, the materials used in some older types of brake pads caused gas to build up between the rotors and pads. That gas also limited stopping power. The last reason is water. If a car drives through a puddle, a carwash or even a rainstorm, the brake rotors can get wet. A wet brake rotor is slippery and difficult for the brake pads to grab. Having drilled holes on a brake rotor makes it easy for heat, gas and water to be quickly moved away from the rotor surface, keeping the brake performance strong. 

The downside of using drilled rotors on your vehicle is that all of those holes tend to weaken the rotors -- just like punching holes in the wall of a house would weaken the wall. After repeated stressful driving, the rotors can even crack. 

But what if you're into driving performance? Are drilled rotors right for you, or should you consider another kind of brake part for your spirited driving? Keep reading to find out.

Slotted Brake Rotors

Slotted brake rotors are great for high-performance braking; however, you'd better be ready to change the brake pads more often.
Slotted brake rotors are great for high-performance braking; however, you'd better be ready to change the brake pads more often.
Brent Melton/iStockphoto

Slotted brake rotors u­se slots carved into the flat metal surface

to move gas, heat and water away from the surface of the rotors.

You can think of the slots as irrigation ditches that move the unwanted materials safely out of the way.

Slotted brake rotors are popular with performance car drivers because the type of driving they

do puts a lot of stress on the rotors. As we mentioned on the previous page, drilled rotors have been weakened, which makes them prone to cracking around the holes, particularly when they've been repeatedly driven hard. Because they tend to be a little more durable than the drilled brake rotors, slotted brake rotors may be a better brake part choice for some performance car drivers.

Of course, slotted brake rotors aren't perfect, either. They tend to wear down brake pads very quickly. Because of this, the most common type of performance brake rotors found on production performance cars are of the drilled variety. While that type of construction is seen as too weak for racing applications, most everyday drivers should have no trouble with drilled rotors on their street cars and can save the slotted rotors for cars that are racetrack-bound.

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So how much different are car and truck brake parts -- particularly car and truck brake rotors -- from motorcycle brake rotors? Read the next page to find out.

Motorcycle Brake Rotors

Of course they're functional, but motorcycle brake rotors often have a decorative appearance, too.
Of course they're functional, but motorcycle brake rotors often have a decorative appearance, too.
Franz-W. Franzelin/iStockphoto

­Motorcycle brake rotors work much in the same way as car brake rotors. The rotors spin along with the wheel, and when the brakes are applied, the brake pads grab the rotor to stop the wheel from spinning. On a motorcycle, however, the front and rear brakes usually operate independently of each other, in contrast to car brakes, which work to slow or stop all four wheels at once. Most motorcycles have independent, hand-operated controls for each brake -- front and rear. The front brake tends to be more effective; delivering the lion's share of the stopping power, with the rear brake assisting to slow or stop the bike. Obviously, motorcycle brake rotors are considered a key component of motorcycle safety. 

Most street driven motorcycles come equipped with drilled brake rotors; however, most high-performance or on-track bikes will typically use slotted rotors. Since motorcycle brake rotors are more visible brake parts than car brake rotors -- especially on the front wheel of the bike -- the drilled brake rotors often provide a custom look. In fact, many custom cycle builders use decorative drilling or shaping of their rotors to make their bikes stand out. 

Stopping a motorcycle takes a relatively small amount of effort compared to bringing a heavy-duty truck to a halt. Find out about truck brake rotors in the next section.

Truck Brake Rotors

Large trucks place a lot of stress on their braking systems. The brake rotors have to be heavy-duty to hold up under the pressure.
Large trucks place a lot of stress on their braking systems. The brake rotors have to be heavy-duty to hold up under the pressure.
TIM MCCAIG/iStockphoto

­Because trucks are so big and heavy, their brake rotors are especially important brake parts.

It takes a lot of force to stop a truck. Slowing down or stopping a heavy vehicle requires, among other factors, a lot of friction from the brakes. The friction between the brake pads and the brake rotors generates a lot of heat, too. The extra weight and heat means that the rotors in a large truck are under a lot more stress than they would be in a smaller vehicle. 

Even with the extra stresses truck brake rotors are under, they're still largely the same as the ones used on cars and smaller trucks. Truck brake rotors tend to be made of cast iron or steel, and they're typically much larger than the brake rotors found on cars. However, truck rotors may require service more often than car rotors. That's not because the rotors themselves don't last, but rather, due to the extra stress of stopping a truck, the truck's brake pads tend to wear out more quickly. If worn brake pads aren't changed early enough, they can cause damage to the brake rotors. Worn pads can scratch or even warp the rotors to the point where they need to be either machined to a new smooth surface or replaced. While this can (and does) happen on cars too, it tends to happen more frequently on heavy trucks because their brake pads tend to wear out sooner. 

Read the next section to find out the brake part that makes all the difference to high performance drivers on the street and on the track.

Performance Brake Rotors

High-performance brake rotors are used on the street by enthusiasts and on the track by professionals.
High-performance brake rotors are used on the street by enthusiasts and on the track by professionals.
JOSE LUIS ROCA/AFP/Getty Images

­Some brake parts get less attention than others. That's just the way it is. For example, high-performance brake pads tend to get a lot more attention than high performance brake rotors. As we mentioned earlier, when you're talking about high performance rotors, slotted, not drilled, rotors are the choice of most racers. The benefit of the slots is that they allow hot gases, water and other debris to move off of the face of the rotor; however, they do tend to wear the brake pads down faster. That's likely not a problem for most performance drivers. Most probably already have ceramic or carbon fiber brake pads which are pretty long-wearing anyway.  

High performance brake rotors are also vented to allow even more heat to dissipate away from the braking system and prevent brake fade. While the slots in slotted brake rotors are carved into the face of the rotors, the vents run around the edge of the rotor. As the rotor spins, the heat escapes through the vents. Without the extra heat, there's less of a chance for brake fade, which makes the car perform better on the track. 

If you're thinking about slowing down or stopping, this isn't a good time. The next page is full of lots more information about braking, brake rotors and other related topics -- just follow the links.

Related HowStuffWorks Articles

More Great Links

More Great Links

Sources:

  • Auto Parts Warehouse. "Brake Rotors." (Nov. 6, 2008) http://www.autopartswarehouse.com/search/?Ntt=Brake+Rotors
  • Brakes R Us. "Performance Brake Rotors." (Nov. 6, 2008) http://www.brakesrus.com/performance-brake-rotors.htm
  • Toboldt, William K. Johnson, Larry and Gauthier, W. Scott. "The Goodheart-Wilcox Automotive Encyclopedia." The Goodheart-Wilcox Company. 2006. (Oct. 30, 2008)