Galfer Wave® rotors are made of a proprietary 420 high carbon stainless steel for increased memory retention during heat cycles
HOW OVERSIZE BRAKE ROTORS WORK
When you think about performance and how to win races, it’s speed and horsepower that quickly comes to mind. Although the power of your motorcycle is an important factor, controlling that power is equally as important in the recipe to get you to the podium. All of that forward momentum needs to be slowed and stopped at the appropriate times on your way to the finish line and that control comes from your brakes.
Many riders replace their stock brake rotors with oversized aftermarket rotors from companies like Galfer and Braking USA. What exactly is an oversized brake rotor going to do for you that the stock rotor won’t, to help you get into that win column?
First, it’s best to understand how the whole braking process works in order to understand how an oversized rotor improves it.
Disc brake basics
Force transmitted from your brake lever to the calipers hydraulically causes them to squeeze the brake pads against the rotor. Friction between the pads and the disc slows the disc down. Pretty simple so far, however a moving motorcycle has a certain amount of kinetic energy built up, and the brakes must remove this energy from the bike in order to stop it. How do the brakes do this? Each time you stop your bike, your brakes convert the kinetic energy to heat generated by the friction between the pads and the disc. The quicker you can transfer kinetic energy to heat and remove the heat, the quicker you can stop. The rotor dissipates the generated heat over the surface that is not in contact with the pads. The larger the surface, the greater the cooling area. Heat that transfers to the rotor must be dissipated or the rotor will warp. Warping is most often caused by excessive heat buildup. It’s all about removing energy from the motorcycle by converting it to heat witout overheating the parts that are performing this function.
The main causes of overheating are: undersized/overmachined brake rotors and/or excessive braking in racing situations or when descending hills/mountains.
Larger Diameter Rotors
The advantage of a larger diameter disc is that it provides more stopping power, and better cooling by transferring kinetic energy to heat and removing that heat quicker than a stock rotor is capable of. The oversized rotor does this because the portion of the rotor that is dissipating heat is larger than that on a stock rotor, allowing the oversized rotor to manage more heat faster. The larger surface on the oversized disc dissipates the heat quicker because of this larger “cooling” surface that is not in contact with the brake pads. The area that is in contact with the pads is where all the friction and heat are being generated. The advantage of oversized rotors is this ability to whisk away more of the heat that is being generated.
A common disadvantage, especially with offroad motorcycles, is that the larger size rotor has a greater chance of coming in contact with something potentially damaging, like a rock, fallen tree or even the motorcycle of another racer.
Oversized wave rotors are designed with a wave along the edge instead of the perfectly round edge of a standard rotor. This allows the rotor to cool even more efficiently. On a normal round rotor, the leading edge of the brake pad is in contact with the entire height of the rotor as the pressure is applied. Because the contact covers the entire height of the rotor heat takes much less time to occur and you end up with heat related problems like brake fade, thermal lock up and inconsistent braking performance. What the wave pattern does is take the leading edge of contact between the blade and pad and constantly move it up and down, thus minimizing heat build up and its inherent problems.
Rotor warping occurs when there is excessive heat and the disc's friction area is at a substantially higher temperature than the inner portion causing the thermal expansion of the friction area to a greater degree than the inner portion of the rotor. Floating rotors were designed to eliminate this problem by creating a separate inner portion and allowing the friction area to float. "Floating" rotors decouple the friction area from the inner portion and allow thermal expansion to occur at different rates that would otherwise warp a solid rotor.
Benefits of better braking
The benefits of all this kinetic energy and heat management is immediately evident once you’ve made the conversion from stock rotors to oversized wave and floating rotors. For motocrossers it is the ability to brake later in corners that oversized rotors allow that translates into lower lap times. For offroaders in sitiuations of excessive braking such as long down hills you will eliminate the risk of of warping your rotor, eliminate brake fade while improving the overall feel of your brakes. With an oversized rotor you will experience more consistant braking under excessive braking conditions without the common heat related problems normally associated with heavy braking improving your confidence and riding.