The 2006 KX450F has just begun arriving at dealers here in the United States. As you will see below, this is quite a motocross weapon.

First, a little background. Kawasaki is certainly “late to the party” with a 450cc four-stroke motocross machine. It is frankly hard to remember when Yamaha blew this category apart with the first YZ400F (was that seven years ago?). It has been a long time.

Every major Japanese motorcycle manufacturer has responded to Yamaha’s class-defining four-stroke. Kawasaki is the last of those manufacturers to respond, and the 2006 KX450F, the subject of this report, is an entirely new machine from the ground up.

When you think about a brand new bike, you may wonder whether it is dialed in, or whether you should wait for future models. We can’t comment on reliability at this point, just performance, but our testing indicates that the KX450F is definitely dialed in, and is one of the most impressive first-year motocross machines we have ever ridden.

How did Kawasaki develop a bike that is so good right out of the box? For one, they drastically changed their original prototype. Take a look at our article on April 10, 2004 and the photo therein of the prototype KX450F being tested during that time frame. The frame on that prototype is completely different from the production machine. Kawasaki made drastic changes to their early prototype in order to reach a production machine that they were happy with. The results are impressive.

The aluminum-framed production 2006 KX450F features a 449cc DOHC, four-valve engine fed by a Keihin FCR40 mm carburetor. The motor features hand-finished intake ports, titanium valves and aluminum valve retainers. Double valve springs are intended to prevent valve float and should increase the durability of the top end.

With both an automatic compression release and a hot start system, the KX450F is claimed to start easily and quickly. This machine is cooled by high-capacity radiators with tightly-packed radiator cores and a new fin design claimed to improve heat dispersion.

The exhaust pipe is made of titanium and tapers in diameter from 38mm to 41mm.

Kawasaki built the KX450F aluminum frame out of forged, extruded and cast parts in an effort to optimize the rigidity for improved handling.

Unlike the KX250F, the KX450F features Kayaba suspension components, including the latest Kayaba forks that place oil and air in separate chambers. The suspension, of course, is fully adjustable for compression and rebound, as well as rear spring preload.

According to Kawasaki, the petal shaped brake discs reduce unsprung weight and help keep the brake pads clean for more efficient performance.

The KX450F is very slim, and the ergonomics are hard to fault (and are complimented by a genuine Renthal aluminum handlebar). Our tall test rider was able to move on the bike easily, and without catching his clothing or boots anywhere.

Both the foot pegs and the foot peg brackets are titanium — indicating the lengths which Kawasaki went to reduce overall weight of the KX450F.

Our vet/pro test rider Russ Somers rode the KX450F at the Competitive Edge Motocross Park here in Southern California. At the end of a long day of riding, Russ found it hard to criticize the big Kawasaki.

The motor is extremely smooth, the power is strong right off the bottom and the bike revved out well. This might be the smoothest motor in the 450 class. This makes the acceleration of the bike somewhat deceiving, but it is definitely very fast.

The suspension on the KX450F is outstanding. Russ has tested plenty of bikes, and spent a few years testing for one of the better known motocross suspension tuners here in Southern California. He stated that the new Kayaba fork on the KX450F is “probably the best stock fork he has ever ridden.” The shock did its job well, but the fork really stood out.

At one point, Russ accidentally over-jumped a large table top at the track. In fact, he over-jumped it by more than 10 feet, landing on the flat and expecting a painful impact. The KX450F fork soaked up this landing so well that Russ was amazed. Keep in mind that Russ weighs over 200 lbs., and this says quite a bit about the bottoming system of the KX450F fork.

In addition to its ability to handle huge hits, the suspension on the KX450F was plush everywhere on the track and allowed the bike to track extremely well in corners. The KX450F genuinely corners like a smaller machine. This cornering ability is combined with good stability, as well, avoiding the normal trade off of increased head shake.

The only negative comment Russ could come up with concerned the transmission. The ratios of the four-speed transmission are fine (particularly, given the broad spread of power), but Russ accidentally caught neutral between first and second on more than one occasion, while using first gear to exit a slow corner. We did not hear other riders complaining about this, so we can probably chalk this up to a new transmission that would shift better once broken in.

All-in-all, the 2006 KX450F is a remarkably solid package for a first year machine. If our testing is any indication, most buyers will not be going to an after-market suspension tuner for fork work — the fork works stellar right out of the box.

As we said at the beginning, KX450Fs are showing up at dealers here in the United States now. The U.S. MSRP is $6,799.00. Take a look at Kawasaki’s web site for additional details and specifications.

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