I've seen two-wheel drive bicycles and motorcycles before, but it always seemed to be a bit of a novelty. Too much added complexity for too little of an advantage.
Apparently Christini has gotten it down to a simple system that works.
The AWD system makes the motorcycle noticeably easier to ride and substantially reduces rider fatigue, allowing you to ride faster for longer periods of time. The AWD system can be turned on and off with a simple flip of the engagement switch. The mechanical Christini AWD system provides distinct advantages without compromising the performance of the motorcycle. Power that would otherwise be lost due to wheel spin is transferred immediately to the front wheel. The system adds just 15 lbs additional weight and has a power loss of less than 1/10th hp.