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"  Steve Christini&amp;#039;s first all-wheel-drive bike\u2014his senior mechanical engineering project from Villanova\u2014hangs near the main entrance of Christini&amp;#039;s shop in downtown Philadelphia. That first bike used a series of chains, shafts, and pinions to transfer power to a suspended, steerable front wheel. His latest two-wheelers\u2014a line of all-wheel-drive off-road racing motorcycles\u2014get power to their front wheels in much the same way. But rather than being prototypes hanging on the wall, they are competing on the world stage at venues like the X Games&amp;#039; Enduro X and Erzbergrodeo enduro. A few years ago Christini sold $3995 add-on kits for KTM and Honda dirt bikes. In 2011 Christini began selling their own brand of motorcycles, with Paoli front shocks and Honda 450X-clone four-stroke or Gas Gas 300 two-stroke engines. The Gas Gas bike is 40 pounds lighter, has a six-speed gearbox, better rear suspension, and the fantastic Gas Gas 300 two-stroke engine. It&amp;#039;s also $2100 more expensive, at $8995, compared with the $6895 450. We got to try out Christini&amp;#039;s AWD bikes. Here&amp;#039;s what we learned. The Tech: The front wheel on a Christini motorcycle freewheels, as it would on an ordinary rear-drive bike, unless the rear wheel loses traction. Thus, it acts like a rear-wheel-drive motorcycle until the rear wheel slips\u2014that&amp;#039;s why it&amp;#039;s AWD rather than 2WD.  The front wheel is under-driven compared with the rear wheel, at a ratio of 0.62:1. That means the rear wheel has to be turning significantly faster than the bike&amp;#039;s forward speed for the front hub&amp;#039;s sprag clutch to engage and begin driving the front wheel. This allows easy cornering, since the wheels can turn at different speeds during a corner. Compare that with a Rokon\u2014a utilitarian 2WD motorcycle used by hunters\u2014where the wheels turn in lock step and are always driven at the same speed. &amp;quot;Our [AWD] drive ratio is what allows the bike to feel like a normal bike, except when you need it,&amp;quot; Christini says.  Christini&amp;#039;s system uses simple machines to get power from the engine to the front wheel. A chain takes power from the bike&amp;#039;s gearbox and routes it through a slipper clutch, then through a driveshaft under the gas tank. The driveshaft pierces the head tube and turns a bevel gearset, which in turn spins shafts that drive stepover chains in the fork crown. A sprocket at each side of the crown turns a telescoping driveshaft in front of each fork leg. Finally, a ring and pinion gearset rotates power ninety degrees to turn the front wheel. The setup adds roughly 12 pounds to the weight of the bike, and Christini says the system saps just 0.1 hp when freewheeling. The AWD can be retrofitted to older bikes, but a custom gas tank must be fitted that allows space for the driveshaft. The system is durable, waterproof, and Christini offers all replacement parts.  The Ride: We rode both Christini motorcycle configurations\u2014the 450 four-stroke and 300 two-stroke\u2014on sandy trails in New Jersey (before Hurricane Sandy&amp;#039;s wrath rolled in). On the 300, with the handlebar-mounted lever flipped to all-wheel-drive and the throttle twisted to the stop, it feels like the bike is bogging down. In reality, the front wheel is using the power that would have produced a big boost.  The driven front wheel benefits the rider in ways beyond pure acceleration. AWD makes it possible to get started on a muddy climb rather than having to dismount and push. In sandy corners the front doesn&amp;#039;t dig in or wander. And since the front wheel keeps turning, the bike tracks exactly where it is pointed. As you exit a corner, it&amp;#039;s possible to get on the power harder and earlier than on a conventional dirt bike.  Trevor Franklin of Motorcycle News once described a Yamaha R1 with a prototype Ohlins hydraulic AWD system as &amp;quot;different\u2013with a strange taut, alert feeling to the front wheel, almost as if it&amp;#039;s electrified\u2013but there&amp;#039;s nothing to &amp;#039;ride around&amp;#039; and it doesn&amp;#039;t demand a change in riding style.&amp;quot; He&amp;#039;s exactly right. Properly done, an AWD bike is alert and connected, but feels natural.  &amp;quot;People think the system uses more horsepower,&amp;quot; Christini says, &amp;quot;but when you&amp;#039;re riding a dirt bike on a sloppy trail, you&amp;#039;ll use less. The reason is because you don&amp;#039;t waste gas and energy on wheelspin.&amp;quot; He also claims that rear tires on an AWD bike can last up to three times as long, since riders aren&amp;#039;t spinning their wheels and burning up rubber. It&amp;#039;s also easier on the rider. The military has just issued Christini a contract for a batch of the AWD 450s\u2014the 450 bested all other bikes in the military&amp;#039;s incline test\u2014and its tests showed that the AWD bike required 30 percent less effort to ride than other bikes. Christini added an auto clutch for the military version and is working on combat-specific upgrades.  The Bottom Line: It may be more complicated than a normal motorcycle, but everyone loves a competitive advantage\u2014witness the popularity of retrofitting centrifugal auto clutches to enduro bikes. AWD offers an even greater benefit. After riding the Christinis and feeling firsthand how a powered front wheel can energize a bike, we&amp;#039;re convinced that there&amp;#039;s a place for AWD on bikes that see extreme conditions. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/cars/motorcycles/a8247/how-to-build-an-all-wheel-drive-motorcycle-14466480/>