What are brake discs?

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Brake rotors slow wheel spin and stop vehicles, with various materials and designs available. Cross-drilling is no longer used on racing vehicles, but is common on high-performance motorcycles and mountain bikes. Carbon and ceramic rotors are lighter and stronger than iron, but more expensive. Warpage is a common problem that can be corrected through machining, but rotors can only be machined a certain number of times before needing replacement.

Brake rotors are the parts inside a car’s wheels that are squeezed by brake pads to slow wheel spin and stop the vehicle. Depending on the type of vehicle, your brake rotors can be made in a variety of materials and designs. Some are made of heavy cast iron, while others may be made of carbon, Kevlar, or other more specialized materials.

Some brake rotors are cross-drilled, which means they have small holes drilled through them. This was originally done on racing vehicles, because gas would sometimes get trapped between the brake rotors and pads, impairing performance. Since modern brake pads don’t have this problem as much as old ones, and because brake rotors can eventually crack where holes are drilled, cross-drilling is no longer done on racing vehicles.

Cross-drilling is now more common on high-performance motorcycles and mountain bikes, such as those used for downhill racing. The purpose of this is to aid in the dissipation of heat that could otherwise warp the rotor when the brakes are applied quickly. Brake rotors can also be slotted, a process in which shallow slots are carved into the rotor, accomplishing the same task on race cars that used to be cross-drilled. Slotted rotors are neither necessary nor practical for most cars, as they cause brake pads to wear quickly, and excessively worn brake pads can lead to damaged rotors.

While iron and steel are the most common materials for brake rotors, others may be used on certain vehicles. Reinforced carbon is a common choice for race car brake rotors due to its superior high-temperature performance compared to iron. Carbon is also much lighter than iron, which is an important consideration in racing.

Slightly less common than carbon rotors are those made from ceramic materials. Once again, the main advantage in this case is light weight, as well as low maintenance requirements. They are also strong enough to tolerate high temperatures, but are significantly more expensive than iron.

There are several ways that brake rotors can become damaged. Excessive rust is a hazard in rotors made of iron, for example. A small amount of rust is universal, but it is possible for the rotor to rust to such an extent that it needs to be replaced. Warpage is perhaps the most common rotor problem. When a rotor warps, excessive heat causes a disproportionate expansion of the braking surface of the rotor. This can cause vibrations in the steering wheel and elsewhere when braking.

To correct this problem, the rotor is removed from the car and turned through a machining tool to give it a smoother surface. This can only be done a certain number of times before the rotor needs to be replaced. Other problems are somewhat less common, such as cracking in cross-drilled rotors or scoring that occurs when worn brakes cause scratches and gouges on the rotor surface.

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