The '06 KX450F proved to be an effective weapon on the track and dazzling in the Dirt Rider 450cc four-stroke motocross shootout (March '06). Talk about a first-year effort! Not that the bike was perfect, but nimble handling, a willingness to change direction and smooth, controllable and reasonably bountiful power made it likable despite suspension flaws and minimal top speed. Kawasaki easily could have glossed the bike with minor updates, fine-tuning and bold new graphics, but it gave the 450 more than 50 updates-the attention a motocross flagship deserves. From the outside, only the black "Diamond Like Carbon" on the fork tubes slaps you in the face, but the major updates stay hidden until you stop kickin' the tires and start using the kickstarter. Once it begins making four-stroke sounds, you will never mistake the '07 mega-motor for the tame-by-comparison '06. It sounds nasty-fast as soon as it lights, and one trip through the gears-five this year-will end any doubts. We wouldn't be surprised if the KX-F is the new horsepower king of the class. It isn't that the power delivery has any violent jumps or brutal hits-it's all hit. There isn't any spot in the rpm range that the engine isn't making gnarly boost. If you have any compassion for the life of the rear tire, you will shift early, and the first four gears are used up pretty quickly, so having fifth is a bonus on faster tracks. When it realized that the '06's four-speed wouldn't cut it, Kawasaki raised first gear a tiny amount (from 1.80 to1.75), didn't change the second through fourth gear ratios at all; it simply slipped in a fifth gear. Suffice to say, if you don't get the holeshot or land a jump short, look in the mirror-it certainly won't be because you didn't have enough motor. We were too busy having fun with the power to worry about tire life, and both front and rear tires shed their edges in a hurry.
Kawasaki generated the newfound boost through an impressive list of engine changes that included new cam profiles, a revised ignition, a tapered midpipe and an intake port that is larger near the valve and treated to a refined finish. As the black fork legs hint, though, the engine isn't the whole story. A revised frame has main spars with more flex. More progressive linkage and a modified rear shock accompany a fork that is definitely more supple. The tube coating is merely the gleam of the iceberg. The fork internals feature cartridges grown from 22 to 24mm and compression pistons upsized from 27 to 30mm as well as tuning on the midspeed valve and the secondary damping. Both ends of the machine have better control and a more solid feel. No doubt the 18mm shock shaft and changes to the shock's compression adjusters all play a part, but the bike is more calm and planted through bumps when entering or exiting corners. One of the assets of the 450 is its effortless control that gives it a nimble feel while jumping. Refined suspension action only makes it better. Timing rhythm sections feels natural, and the bike flows through transitions. Crisp steering helps, and the bike handles flat turns pretty well. And it loves berms and ruts.
When the track surface is varied and the bumps are deep but with unusual placement, the rear will give the odd kick-up, and if your weight isn't balanced equally on both pegs, the rear might kick to the side more than other bikes.
The rear of the bike feels a little low to tall riders, but otherwise it has very mainstream ergonomics that rarely intrude on your mind while you are riding. The Renthal bar has a likable bend and a good feel. The brakes are strong but not sudden. In short, the KX-F does more than its share on the track-you just need to handle your end. Part of that is to be smooth and conservative with the throttle. The bike has enough boost to light the tire in critical traction situations, so if you aren't paying attention, you may end up checking soil conditions with your elbow. Ride like you're supposed to, though, and the competition will feel the track blasting them from your rear tire.