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Transfer of Power
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Christini Honda CRF250X AWD
Don Williams
10/01/2007
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Photography by Justin Dodd
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Although
two-wheel-drive motorcycles are nothing new—Rokon has been offering its
Trail-Breaker go-anywhere machine for decades—a high-performance motorcycle with
two driven wheels has until now been an unattainable Holy Grail. Yamaha tried it
recently, but its hydraulic system’s performance was more theoretical than
practical. The bike disappeared quickly, never making it to the United
States.
 RIDING STYLE
Helmet: Axo Chute
Goggles: Scott VoltageX
Jersey: Axo Sport
Gloves: Axo Ride
Pants: Axo Nickle
Boots: Axo RC6. (Click image to enlarge)
The Da Vinci Code of two-wheel-drive motorcycles, however, has
been broken by Steve Christini, an engineer who designed an all-mechanical AWD
mountain bike as his senior project at Villanova in 1995. Christini eventually
took the mountain bike to market, but only 50 of the AWD bicycles were sold.
Ultimately, the increased weight and slight power loss were insurmountable
obstacles for riders of a self-powered vehicle.
The experience turned Christini’s attention to off-road
motorcycles, where the prodigious benefits of 2WD benefits stood to far outweigh
the system’s nominal liabilities. Rather than build an entire motorcycle from
scratch, Christini made the decision to modify existing machines—the Honda
CRF250X, initially, followed by the 450X and 250R, and, soon, various KTMs.
 The patent-laden Christini Technologies system is simply
ingenious. It is easy to understand, yet contains enough engineering tricks to
thoroughly impress. It is a remarkable sleight of hand that the system
dissipates a mere 1/10th hp and adds only 15 pounds, according to the
company. (Click image to enlarge)
To start the transfer of power, a second sprocket is
piggybacked with the countershaft sproket, which runs a chain up to a sprocket
in the Christini-modified frame. A clutch-damped shaft transmits the power to
the head tube, where counter-rotating bevel gears move the power to the lower
triple clamp. Two chain-and-sprocket pairings then send the power to the
trickest items on the bike—telescopic driveshafts with linear ball spline
bearings. The counter-rotating driveshafts run parallel to the forks into the
fork gearboxes, then into a modified Talon hub containing one-way clutches to
drive the front wheel at 75-percent of the speed of the rear.
 This last piece of information is critical. Rather than a
full-time two-wheel-drive system that powers the front wheel fulltime, the
Christini is an on-demand AWD system that only propels the front wheel when the
rear wheel spins. Once the front wheel matches the rear in speed, it returns to
freewheeling. (Click image to enlarge)
As with any new technology, the proof is in the riding, and the
Christini absolutely delivers. Although Christini has revolutionized the
motorcycle drive method, the effect of the system is startling in its
transparency. No special techniques are required to ride the bike effectively.
The design simply does what it is supposed to do—act as a traction control
device and the clutch systems preempt any abrupt introduction of power to the
front wheel, eliminating fatiguing and control-threatening jolts.
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