Reverse-Rotating Rotors Update
By Kevin Duke and Bart Madson
In February we received an intriguing press release about a new invention in the motorcycle world. Inventor Robby Kasten had come up with a potentially revolutionary design to "eliminate speed-related steering effort while increasing stability." His idea was Reverse Rotating Rotors (RRR) which would counteract the gyroscopic effect of the front wheel by spinning the rotors in the opposite direction of the wheel.
It was an idea that piqued our interest and one we planned to keep an eye on. Now word has reached us that Kasten has just finished testing his prototype on the street and, even more recently, out on the track at the Jennings GP raceway in northern Florida.
Kasten's idea first came to him about six years ago when out riding with friends. One of them suggested he try counter-steering: the act of pushing the handlebar in the opposite direction of the way you want the bike turned. After some initial skepticism about the technique, which seems counter intuitive, he's been obsessing about the physics of riding ever since.
In time his attention turned to the specific problem of steering resistance at high speeds. He noted that a front wheel's gyroscopic effect makes a bike harder to steer the faster it turns. The spinning wheel generates torque, so a rider has to provide a handlebar input greater than that torque to turn a bike.
"All motorcycles are harder to turn the faster they go and it makes no sense that we just accept this as though it must be," says Kasten. "In a racing or aggressive riding situation, it is not uncommon for a rider to exert in excess of 100 lb-ft. of torque on the bars in order to change lean angle. Imagine if that sort of effort were necessary to turn a car. It would not be called stability, it would be called deadly."
To counteract the gyroscopic procession of the front wheel, Kasten reasoned that spinning the front brake rotors backward would negate most of the effect, resulting in a bike that is much easier to turn at high speeds. And if the rotors are spun backward faster than the wheel, it could provide a counteractive force equal to the heavier wheel assembly.
Kasten's patented concept is put into practice via a series of three gear-sets. An outer ring gear is pressed into a specially made front wheel, and this gear spins four planetary transfer gears which turn a central cog that drives the brake rotors backward. The gear assembly is held in place by the torque transfer arm that bolts to the stock caliper. It's a remarkably simple arrangement, one similar to that of an automatic transmission.
To test out his design, he's fitted it to a 2004 Kawasaki ZX-6R. In its current configuration, the rotors spin backward at 2.7 times the speed of the front wheel, which is estimated to reduce steering effort by 70%. Kasten admits the gearing will slightly sap horsepower, but he's adamant the benefits far outweigh the cost. To illustrate his point, he notes that a 600cc sportbike is nearly as quick as a 1000 at many tracks despite as much as a 50-hp disadvantage. In addition, the current prototype is massively overbuilt for safety reasons ("It could stop a bus," says Kasten), so its size could be reduced by half.
A video on Kasten's website of these initial tests give a good visual of how the RRR actually looks when it was tested on the street. After those first forays the bike faced the true test of its abilities, and possible potential, when Kasten took it out to the Jennings GP circuit.
"I swear you can think it into corners," Kasten raves. "It behaves just like a conventional wheel except that the bike is really easy to turn. It never gave me the slightest wobble. Under hard acceleration when the front gets light and slightly off center it goes back to straight without any headshake. I did not use a steering damper. This same bike with the stock wheel went into a full tankslapper and nearly pitched me off in the Daytona infield."
Another video from Kasten's website shows clips of the recent Jennings GP test. In a press release issued about the track test, Kasten was encouraged by his design's performance stating: "It was an amazing day. The prototype seems to be bulletproof and it improved the performance of the bike as predicted."
Another benefit of RRR, says Kasten, is its ability to eliminate the dreaded tankslapper. He says rapid lean-angle changes cause the bike's wheels to be misaligned with the path of travel, and this fights against the gyroscopic precession of the front wheel. "If that force is canceled out then a tankslapper is impossible."
The next step in development is to test the RRR assembly on a ZX-10R, a bike with a greater propensity for headshake. The 10R's larger (300mm) brake rotors will have the effect of further reducing gyroscopic force. Kasten says the 6R's 280mm rotors reduce the front wheel assembly's effect from 25-plus-pounds to the equivalent of a 5-pound assembly (tire, wheel and rotors). "When we fit it to the ZX-10R it will be equivalent to what a 3-pound assembly would be."
If Kasten's invention pans out, it would have an obvious application in the motorcycling industry in general, and the roadracing world in particular. Of course, a video can't effectively display the ease of turning for which the RRR is designed to improve, so for now we will have to take Kasten at his word. That is until we test his revolutionary design for ourselves, which we plan to do in the future. We will keep you posted.
For an in-depth examination of Kasten's ideas, you can read through them on his website at www.reverserotatingrotors.com. He addresses several basic concepts of the physics involved in riding a motorcycle, including a special section with accompanying video to explain why RRR works.