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THROTTLE JOCKEY / SUSAN CARPENTER

Quick: Bike Or Bronco?

Try staying on Kawasaki's snortin' KX450F. It's no wonder supercross is soaring lately.

December 06, 2006|SUSAN CARPENTER

AS I flew through the air at Lake Elsinore, there was a point when I marveled at the power of the new 2007 Kawasaki KX450F motocross bike. That was after I'd lifted off from my bunny jump but before I landed rubber side up, grinding my shoulder into the dirt.

There's a reason low-caliber dirt riders such as me don't ride grade-A motocross bikes of the four-stroke, 450cc variety. They're missiles in Skittles-colored clothing. But heading into supercross season, I wanted to get a taste of the technology that's driving racers, and the sport itself, to new heights of derring-do and popularity. That led me to the KX450F -- the bike helmed by highflying hotshot James Stewart, who's favored to win the upcoming AMA Supercross Championship Series now that reigning champ Ricky Carmichael is racing an abbreviated schedule.

The 2007 is only the second model year for the KX450F, and already it's gotten a major reworking. Ordinarily, Kawasaki bikes are on a two-year product improvement cycle, but the company made more than 50 changes to the KX450F. The pace of motocross technology and the rate of adoption required to stay competitive are that fast.

Over the last decade, off-highway motorcycle sales have quadrupled, from 79,000 in 1995 to 318,000 in 2005. The Motorcycle Industry Council doesn't break out individual sales figures for play bikes, dual sports and motocrossers, but the sold-out supercross events at Anaheim, maxed-out motocross tracks and six-figure endorsement deals are strong indicators that competition models are a pretty big piece of the pie.

On the KX450F, some of the most significant changes were the intake (which was revised with new camshafts) and a tapered (rather than straight) exhaust, both of which work together to give the bike better low-RPM performance, low-end torque and acceleration out of corners. The aluminum twinspar frame was also tweaked to give the bike less torsional rigidity, i.e. to allow a little more flex and better handling when ridden like a bronco.

The diamond-like coating on the Kayaba fork tubes is also new. An industry first for a production motocross bike, the coating helps smooth the fork action as the front end works its way around the track. Then there's the extra gear. Last year's model had four, but the pros were topping out on particularly fast tracks, so the '07 model has five.

Personally, I never got past second, which seemed plenty fast as I carved the berms, bobble-headed the whoops and rolled the jumps I was too chicken to fly over by more than a few inches.

What hasn't changed with the '07 model: the 38-inch saddle and the kick start, both of which freaked out my street-riding self, especially in combination. The 38-inch seat helps give the bike 13.58 inches of much-needed ground clearance down below, but I wasn't so sure I could throw a leg over, even though I'm 5 feet 8 and can look many pro motocrossers in the eye.

It wasn't as bad as I'd feared. For maximum suspension performance, the bike is best with about four inches of sag in the rear. The sag in the back balances the chassis with the front and allows the wheels to drop into and pop out of the bumps and ruts on the course.

Adjusting the spring brought the saddle down to 34 inches when I put my weight on it, so I wasn't SOS (seat off seat), just tippy toe. Of course, that doesn't matter once you get going -- only when you're stopped. Or you've wiped out, as I did.

That brings us to the kick start. There's only one 450cc motocrosser on the market with an electric start on the grip, and the KX450F isn't it. Competition off-roaders don't have them because an electric start can add 5 to 10 pounds. On a 220-pound bike, where every ounce counts, it's a lot of extra weight for no good reason. Anyone wanting a KX450F with an electric start will have to wait for the 2008 KLX450R -- the off-road version of the purpose-built, closed-course KX450F.

Ever ridden one of these range ponies? It'll give you more respect for the racers who'll be kicking up the dirt when the championships kick off in Anaheim next month. Even without the fine-tuned motor, stiffened suspension and other performance enhancers, the KX450F is a monster of a machine.

Stock engine performance is one of the reasons motocross is becoming more of a four-stroke world. You don't need to spend a lot of money and time futzing with performance pipes and other mods; they jump hoops right out of the box. The power delivery is also less abrupt and more linear on a four-stroke.

Until the late '90s, when Yamaha rolled out its four-stroke 400 prototype, motocross was a two-stroke affair. Manufacturers just didn't believe it was possible to make a four-stroke motocrosser that was powerful, compact and lightweight enough to compete. But the Yamaha YZM400 proved it could be done. By 2003, Honda had jumped on board with a four-stroke 450. Then came KTM, Suzuki and, just last year, Kawasaki.

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