Reinventing the (front) wheel

On most motorcycles, that front wheel doesn't do a whole lot. Christini's all-wheel drive puts it to work. Photos: All-wheel-drive motorcycle

What happens when you breed a helicopter with a two-wheeler? You get a motorcycle with all-wheel drive.

Philadelphia-based Christini has begun to market a drivetrain that can apply power from the engine to the front wheel of motorcycles. A second chain turns the front wheel so that riders can get through sand, snow, mud or uneven terrain more easily.

"I love it. It is a total advantage," said Mike Bergman, a professional motocross racer who's raced twice on motorcycles equipped with Christini's drivetrain. "Let's say you come into a rough corner with deep ruts, it will pull you right around it."

Christini recently released a version of its drivetrain for some Honda dirt bikes and will soon have a unit that works with off-road motorcycles from KLM. Over the next few years, it hopes to move from selling its system as an aftermarket device to something that is integrated into a motorcycle at a much lower cost at the factory.

Eventually it will also come to street bikes because it can increase safety and handling, according to founder Steve Christini.

"The average rider gets the most benefit out of this," he said. "The benefit of all-wheel drive is control, stability, safety and cornering. It keeps the front end from washing out."

The company has all-wheel mountain bikes, too. With bicycles, all-wheel drive allows riders to get up steep slopes without having to stand up and pedal, or down slippery surfaces with less fishtailing.

Although they don't get near the attention that cars do, inventors actively tinker with the technology behind bikes and motorcycles. Shimano recently came out with an automatic transmission for bikes, and Zero Motorcycles and Vectrix have come out with electric motorcycles.

The all-wheel drive concept sounds simple, but it's difficult to execute. Large, established manufacturers have tried out different ideas for putting a second chain on the front wheel, but ultimately backed away from coming out with products.

The difficulty was in how to deliver power to the front wheel without disrupting steering and handling. If you attach the chain to one side of the hub, it will pull the front wheel, and hence the rider, in that direction. One manufacturer spent years on a system that would drive the wheel through pressure hydraulics. Hydraulic systems, though, consume lots of power.

Christini came up with his idea in the mid-'90s during some time off. A friend had a model helicopter and he studied how the engine spun the two separate rotors in two different directions at the same time. He was also an avid mountain biker and wondered how he could improve his ride.

The Christini system essentially involves taking a helicopter drivetrain and adapting it to the fork of a motorcycle or bike. In a helicopter, the engine turns a gear. Instead of turning a chain (and a wheel) directly, that gear is attached to two other gears, which turn separate chains that then power the two rotors.

In Christini's drivetrains, a chain runs between the main cog (the big gear that's also attached by a chain to gears on the rear wheel) and gear inside the head tube. The head tube then transfers power to two separate drivetrains on the left and right of the fork. Like on a helicopter, the drivetrains spin in opposite directions, but both work to turn the wheel forward. It's the same principle that allows boats with two propellers to go forward without swirling in circles.

"By having counter rotating shafts, it allows the motorcycle to steer straight. (The gears) are both spinning the wheel forward but they are spinning in opposite directions," he said. "We essentially put a helicopter drive system in a motorcycle."

In ordinary motorcycles and bikes, steering is accomplished by a central bar inside the head tube. The steerer effectively connects the fork to the handlebars. Since the gears are in the head tube in the Christini system, the steerer is attached to the forks.

Christini points out that the system gives riders all-wheel drive, rather than permanent two-wheel drive. The drivetrain kicks in when the front wheel and the back wheel are spinning at different speeds. When that occurs, the system begins to power the front wheel and then shuts off again after equilibrium hits.

"Because you're not powering the front wheel all the time, you're not sucking power all the time," he said.

Bergman said that the steering can occasionally feel a little heavy, but that it's not a huge difference. "You really have to pay attention to notice it," Bergman said.

The company initially marketed the front-wheel drivetrain for mountain bikes and signed a deal with Jeep in 1998 to put it on that company's mountain bikes. Sales though, were never huge.

Although it still sells all-wheel drive bikes, the company began to emphasize developing a product for motorcycles in 2002. It finally began to sell a product, for three types of Hondas, this year.

Adding the system takes some work. The entire frame on the motorcycle has to be swapped. Riders bring their motorcycles to a dealer, who then performs the swap (which takes about four to six hours). It costs $5,995 and riders have to turn in their old frames.

That's steep, he admits. However, the price could drop to $1,500 to $2,000 if manufacturers decide to insert all-wheel drive at the factory.

"Everything new is more expensive when it first comes out. It's a volume issue," he said. "We don't have a single person who doesn't get on this who isn't giddy when they get off of it."

"And let's face it," he added. "There are a lot of people in this country and overseas with plenty of money who want to be first movers."

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