2WD For Motorbikes; Has the Dream come true?

No matter how sophisticated motorcycles get, there is always some bright spark working on something new and amazing. The best of it all is that it’s not only the major manufacturers who are doing the inventing; often it is small companies beavering away on some pretty significant stuff that could change the face of motorcycling.

The Christini Frame

Probably the most significant problem that has fascinated engineers is the issue of 2-wheel drive for bikes. As with 4WD systems for cars, the benefits are obvious but the engineering is vastly more difficult because of the layout of a motorcycle or, more specifically, the situation of the front wheel, which has no obvious direct path along which to transmit the power.

Drive to the headstock

Yamaha and Ohlins have been working (and spending) hard on a system that uses a hydraulic motor to drive the front wheel (called the 2-Trac) and KTM has patented a system that uses an electric motor in the front hub but there is nothing to suggest that we will be seeing these systems on a production bike any time soon.
Similarly, a look at patent applications shows that many of the major manufacturers have been working on 2WD research and development, but have just kept very quiet about it. Quite why, it is hard to understand as the improvements in traction, handling and safety under low-grip conditions have to be the holy grail of any wheeled vehicle design.
However, the veil of secrecy only extends to road bike development. For off-road applications, the manufacturers have been much more open and possibly the only reason that things haven’t progressed further is that major sanctioning bodies for motorcycle sport have banned 2WD from motocross and enduro events. And that can be for only one reason; because it works!

Secondary chain takes drive to top of frame

Step up, Steve Christini from America. The system his company has developed might be the most old-fashioned, relying as it does on a system of mechanical linkage to the front wheel in the form of chains and drive shafts but it seems at this point in time to be the most viable.

Drive to the hubs

The system works like this. A second chain (the rear wheel drive chain being the first!) takes drive from the gearbox countershaft up to a bevel box mounted on the top spar of the frame. From here a drive shaft takes the drive underneath the petrol tank to more bevel gears which direct the drive down the steering stem to the lower triple clamp.  Two small drive chains in the clamp transfer power out to a pair of telescoping shafts, running parallel to the fork legs.

At the front hub, a Sprague clutch – similar to the freewheel mechanism in a bicycle’s rear hub – transfers power to the front wheel when rear-wheel speed exceeds front-wheel speed by more than a prescribed ratio i.e. when there is wheelspin.
Any system that applies positive torque to the front wheel in a turn makes the bike lean in. That “steer-torque” complicated handling enough, so Christini decided to minimize the torque effects of his own system by using counter-rotating shafts, which cancelled each other out. Those two shafts also provide an unexpected benefit: they act as gyroscopic steering dampers, reducing the bump steer effects produced by other front-hub motors.

Drive at the headstock

When you buy a Christini kit, you get a complete new frame, including front fork and wheel, onto which you bolt the mechanicals of your existing bike. There are kits available for Honda and KTM enduro and dual sport models with kits for Gas Gas and Kawasaki in final testing. A kit costs around R35,000 with complete bikes available for R35,000 more (prices converted from US$).
The big issue is not whether 2WD is the future of motorcycling – on- or off-road – or whether it matches ABS as a significant advance in motorcycling, but rather how long we will have to wait to see it on showroom floors.
For more information and to watch videos, go to www.christini.com