When most riders go hunting for speed, they pore over catalogs of engine parts like acolytes searching for illumination. Cams and pistons and pipes, oh my! What they forget in their frenzied search for power is that if they can't slow down from the terminal velocities their mega-motors generate, they'll simply punch a bigger hole in the scenery as they miss the turn.
A better idea, perhaps, would be to take the opposite tack; that is, look for gear that would help them slow down more rapidly, more efficiently and more controllably. And one of the latest weapons in the braking armada for streetbikes is the wave (or petal) rotor. Such rotors were first used on off-road bikes almost a decade ago, and only fairly recently have trickled down to streetbikes.
Galfer U.S.A. uses a special...
Galfer U.S.A. uses a special computer program--COSMOS, one of the most widely used analysis software products--to check the strength distribution in its rotor designs to ensure the rotor is structurally safe.
Several companies make wave rotors these days, and some of them will have you believe the discs not only improve your bike's stopping power, but will get you a hot date on Saturday night, too. In order to sort the truth from the merely interesting fiction we spoke to Sandro Milesi, general manager of Galfer U.S.A. Milesi's grandfather started Galfer Spain in 1946, and Galfer owns the original patent on wave rotors. He's also a straight-talker, so he seemed the perfect person to explain what are the real advantages of wave rotors for streetbikes.
"The main advantage I would say is the feel of the brake system itself," Milesi says. "The idea is to make a rotor that has better brake-lever feel, so that when the guy jumps on the bike he gets a noticeable difference. He says, `Oooh, my brake-lever effort has been reduced,' meaning, `I can squeeze on that brake lever and I've got more bite out of the brake system.'
"When a brake pad finds a brand-new leading edge or a brand-new surface every time, it has better brake-lever feel. It initiates new bite, y'know? So basically that's the whole idea.
All of Galfer U.S.A.'s high-carbon...
All of Galfer U.S.A.'s high-carbon 420 stainless steel rotors are laser-cut, not stamped. Stamping puts unwanted stresses in such high-memory steel.
"The wave shape adds leading edge to the contact between the pad and the rotor. That's very good. So as it rotates, the depth of the cut of the wave is what we believe gives the brake system its feel."
That's not all, though. Milesi mentions that while testing a wave rotor for an ATV application, they found a consistent 20-degree drop in rotor temperature--pretty significant for what is usually a fairly small and overworked part to begin with. So, wave rotors also dissipate heat better than round discs. Why?
"Turbulence, basically. When the rotor turns and the bike is going forward, you're catching fresh air and putting it on top of the brake-pad surface. The rotor continues to turn, of course, and it rotates through the pads. As the pad heats up and releases dust, the heat and dust are actually being pushed forward and out of the rotor along the path of the wave.
"As the path of the wave comes in it brings cold air; but it is also moving heat and pad dust out of the way of the brake pad itself. That's why you'll see on our rotors a wave will have one shape, the next wave a different shape, and then the next back to the first design. So it goes back and forth, back and forth; that's why it dissipates heat better.
Note the irregularly shaped...
Note the irregularly shaped holes. Round holes tend to trap heat and dust, whereas tapered shapes induce turbulence that keeps the heat and dust from remaining stationary.
"Actually I just gave you a pretty good secret," he says, laughing. But aren't wave rotors also lighter than conventional discs?
"I get e-mails constantly from people asking me how much lighter [a wave rotor] is than stock," Milesi says. "Well, sometimes it's not lighter than stock. That wasn't the idea. I have never told our designers the weight of a stock rotor. Because if we're going to design a rotor based on that, just being lighter, you are jeopardizing so much; it's not worth it. It wasn't part of the idea behind wave rotors.
"And when people ask me, `Am I going to get a huge amount of difference [with your wave rotors]?' For street use, probably not. On the racetrack? That I have no doubt about. That's how we designed that rotor. On a racetrack the rider is reaching the area where the rotor was truly designed to outperform, to make a difference. He's using it harder, he's pounding more heat into it.
"We're at the racetrack all the time. If we sell something to you, and it's really worthless, do you think I'm going to be stupid enough to go to a racetrack and face you?"