2006 Kawasaki KX450F First Ride

MotorcycleUSA Staff | October 17, 2005
MCUSA walked away from the KX450F press intro excited about the resurgence of effort in the Green Machine s motocross lineup. We can t wait to see how the bike stacks up against the rest of the 450s in head-to-head combat.
MCUSA walked away from the KX450F press intro excited about the resurgence of effort in the Green Machine’s motocross lineup. We can’t wait to see how the bike stacks up against the rest of the 450s in head-to-head combat.

Let’s face it. No one likes to be picked last, but that’s exactly what has been happening to Kawasaki in the 4-stroke motocross arena. All the other major manufacturers have developed and released their own 250 and 450 models since Yamaha blew the lid off the industry with the YZ400F in 1998.

Last year, Kawasaki revealed a prototype of the KX450F. It was being tested for future competition in the AMA Supercross and Motocross divisions, but instead of releasing the bike for 2005, Kawi decided to hold off releasing its production bike until 2006. The move drew some heat from within the industry and green-blooded consumers stranded aboard their KX250s. Well, the wait is finally over, as Kawasaki assured us by inviting MCUSA out to Competitive Edge Motocross Park in Hesperia, CA for its KX450F press intro.

When Kawasaki was initially developing the KX450F it was vastly different machine from the final 2006 production bike. Basically what it boiled down to is that the aluminum backbone frame was either too stiff or flexed too much. Kawi tried countless versions of the backbone chassis, but could never find that elusive sweet spot to blend rigidity and flex into the perfect combination. From the chassis troubles stemmed a host of other problems that played part in holding the Kawi back. For one, the engine sat at a more horizontal angle, leaning toward the front of the bike. As a result the prototype felt top heavy in corners and had more engine braking than engineers wanted. 

Kawasaki didn’t want to enter the most competitive market on the planet with a sub-par machine. Yamaha was already established, Honda holds down the role as privateers’ choice and Ricky Carmichael has been cleaning house on the Suzuki RM-Z450. We can’t say the original KX450F mule would have floundered in the premier class, but the ’06 production bike definitely has the potential to duke it out with the rest of the big-bore 4-stroke gang.

The production KX received changes across the board, sporting an all-new, twin-spar aluminum frame as the focal point of the new model. Unlike the prototype, the production chassis allows more space above the engine for engineers to rotate the motor into a vertical stance like they did for the KX250F. Even though this may seem like a relatively insignificant change, the overall inertia is lessened because of the compact arrangement. Moving the piston and crankshaft closer to the transmission creates less longitudinal motion that affects engine braking and handling characteristics.

The kickstart lever is a short throw  but the Kawi fires on the first or second kick every time no matter how hot the engine is. Needless to say  we love that.
The kickstart lever is a short throw, but the Kawi fires on the first or second kick every time no matter how hot the engine is. Needless to say, we love that.

We were impressed with the 2006 KX250F’s new aluminum chassis when we got our chance to throw a leg over it. Even though the 450 has an identical looking frame, the two are dissimilar to the point that they are made by completely different companies. However, there are similarities such as the 450 frame also being constructed using a combination of forged, cast and extruded aluminum pieces. The goal, of course, is to create a chassis that has superior rigidity in areas of high stress while allowing the frame to give in areas where more flexibility is needed.

Another key component that made the list for both of Kawi’s MX thumpers is the compact, high-capacity Denso radiators. Overall capacity isn’t jeopardized despite the smaller design thanks to a greater number of cores for coolant to flow through. Radiator shrouds are the two-piece arrangement with black uppers and Kawasaki Lime green on the lower portion. Kawi riders will be able to mix and match color schemes, but the real advantage of the two-piece component is that crash-damaged pieces can be replaced independently, and most importantly, the upper portion of the frame is left exposed to serve as a gripping surface for a rider’s knees. Scooting forward and keeping a tight grip on things with your knees is easy on the 450F and helps make the bike easy to steer everywhere on the track. 

While we’ve been comparing the 450F’s components to that of its little brother, there is a major difference between the two. Kawasaki has been running Kayaba suspension since the dawn of time, but broke the mold for 2006 by bolting Showas on the 250F. As for the new KX450F, well, some things never change, and Kawasaki stuck with Kayaba, opting for a new 48mm, inverted AOS fork system. The shock, also by Kayaba, performs better than the front end. I personally liked the way the rear end moved and handled jumps and acceleration bumps, but the front suspension was a different story.

The frame might look similar to that of the 250F  but Kawasaki assured us that they are completely different. They’re even manufactured by different companies.
The frame might look similar to that of the 250F, but Kawasaki assured us that they are completely different. They’re even manufactured by different companies.

Competitive Edge is an awesome track with elevation changes and a handful of tabletops that give a big-air sensation while remaining relatively safe. The soil was freshly disc-ed and watered when I arrived in the morning, and it took almost half the day to get some good lines cut in. Once the track began to roughen up, I could really start to feel what the suspension was doing. The rear end started to chatter a bit on braking bumps at the entrance to several corners, making it hard to settle into ruts. I softened the high-speed compression on the shock by a quarter turn and it solved the problem, but other than that I loved the rear end.

The front fork wasn’t as easy for me to get dialed. Slapping the front end on jump landings is a common enough occurrence in motocross, and it seemed to be my preferred method for the day at Competitive Edge. However, these front-end-last landings delivered a harsh jolt through the aluminum Renthal handlebars as the fork didn’t want to move through its stroke. After dissecting the problem I was having, I decided to take out a few clicks of compression damping from the fork’s standard setting of 12 clicks out. Thankfully, the adjustments made a huge improvement and really eased the harsh landings, and I was doubly pleased to find that softening the fork’s damping didn’t significantly change how the bike handled on the rest of the track. The fork was still able to handle flat- and front-wheel-first landings with smooth and supple action.

Kawi technicians assured us that R&D riders consistently felt the Kayabas worked better on the 450, but I preferred the Showa’s characteristics of the KX250F. At least the suspension components on the big bike offer a ton of adjustability, which was enough to solve the problem I was having.

Kawasaki wanted to give its new flagship machine a narrow profile for a moto-only application. They succeeded.
Kawasaki wanted to give its new flagship machine a narrow profile for a moto-only application. They succeeded.

One thing the suspension does well, or at least plays a part in, is track the bike through corners with good stability. Despite the alliance between Kawasaki and Suzuki, the KX450F was a completely separate project from the yellow RM-Z450. The division is noticeable at the steering head where the quick-handling Suzook boasts a sharp 25.5-degree rake and 4.4 inches of trail. The KXF on the other hand has a 27.1-degree rake and 4.6 inches of trail. Combined with the awesome chassis the Kawi offers a secure-feeling ride everywhere on the track. Rough straights are easy to negotiate, as are banked and rutted corners. Despite the stability of the KXF, the bike still turns with ease. A neutral center of gravity and well-balanced chassis and suspension allow the green 450 to rail the inside line.

Another feature that aids in cornering prowess, perhaps my favorite, is the petal style brakes on front and back. I loved the 250F’s stoppers and the big brother version is equally powerful with a 250mm semi-floating disc mounted to a dual-piston Nissin caliper at the helm. When I reach for my front brake, I don’t want to feel like Popeye as I reef on the lever. The KXF gives me just what I like in the form of a sensitive, strong brake that requires minimal input at the lever and resists fade. I love this stuff.

The rear 240mm, single-piston Nissin unit is equally as good, combining for a stellar braking package. Kawasaki’s excellent brakes make it easy to stuff the big thumper into an inside line and makes the rider feel comfortable braking late and aggressively. Not only do they work like a champ, but the petal-style design reduces unsprung weight on the 220-pound (claimed) machine. In comparison, Kawi claims 204 pounds for its 250F. 

Deep  sandy loam greeted us at Competitive Edge track where Kawi debuted the KX450F. It s a good thing the bike was a 450  because this stuff would swallow a small-bore thumper or 250cc 2-stroke.
Deep, sandy loam greeted us at Competitive Edge track where Kawi debuted the KX450F. It’s a good thing the bike was a 450, because this stuff would swallow a small-bore thumper or 250cc 2-stroke.

At the other end of the berm, the Keihin FCR40 carburetor-fed, 449cc, DOHC, titanium four-valve engine snarls to life with a satisfying grunt. An automatic cam-chain adjuster, hand-finished intake ports, double valve springs and a low-friction piston skirt allow the engine to rev quickly while putting the power to the ground. A twist of the throttle and it’s go-time as the 450F produces serious torque down low and extends into the upper rpm without hiccups or gaps. Part of the reason for such a smooth powerband is the new all-titanium exhaust pipe that widens 3mm from header to silencer. Inside the can are longer fibers for durability and improved blow-out resistance.

The motor felt sluggish and weak during my first laps. Then I put my foot down and sunk eight inches into sandy loam, and my attitude suddenly changed to one of appreciation. If I had been on a 250 2-stroke or any smaller-displacement bike, that soil would have gobbled it up. But the KXF plowed through the soft stuff with surprising ease. The close-ratio tranny shifted like a breeze, allowing me to get the front wheel on top of the loam and keep the rear digging trenches. I rarely missed a shift even when blowing berms and wallowing through the deepest corners.

Knowing what kind of market they were getting into for 2006, Kawasaki wanted to make the KX450F the best motocross bike possible. As a result, there are a host of features that make this machine moto-specific. The four-speed transmission is the biggest modification that tells a rider immediately that this bike has been purpose built for MX. The KX prototype came with a five-speed, but that was changed on the new model for one simple fact: who the hell actually uses fifth gear on a motocross track when riding a 450 4-stroke?

I’m confident in saying that the engineers made a good decision by shortening the gearbox. The tranny, which is lighter and more compact than the ’05, was perfectly suited to the motor – I always ran out of room on the straights before needing to grab another gear. To be honest, I spent most of my time in second and third, the latter which seemed to be the ultimate utility gear.

JC liked the roll-on power of the KXF.
The all-new Kayaba AOS fork feel good while blasting berms, but require some tweaking to eliminate some minor headshake and harshness on slap-landings.

During the last half of the day was when I could really notice the finer points of the motor. As the track wore in, the tractability and easy roll-on throttle launched the bike out of corners and down straights. A set of new, wide-pattern Dunlops provided excellent traction in the loam. The D742 front has been pumped up to a 90/100-21 spec while the rear is a beefy 120/80-19 D756. Engine braking is more noticeable than a 250F, but getting familiar with the feel of a heavier motor can let riders use that inertia to their advantage, especially when coupled with the stupendous brakes of the KXF.

According to Kawasaki, “this is a bike that really caters to riders with a high skill level.” To illustrate the point, four-time AMA Motocross and Supercross champion and long-time Kawasaki rider Jeff Emig was on hand to put in some laps and showcase the KX450F at speed. That’s precisely what he did, giving me a terrific first-hand view of the bike’s rear knobby. I can tell you that I’ve never been quite as happy about getting roosted as I was riding alongside my favorite rider of all time, though not for long since he went by me like I wasn’t even there. I grew up rooting for Emig as he went from the underdog in Supercross against Jeremy McGrath to the undisputed king of the outdoors for a couple years, so sharing a track and having lunch with my hero was definitely a highlight of the trip to Hesperia.

All of the Kawasaki guys on-hand were great, including three-time champ “Jammin'” Jimmy Weinert who was also there to tell me just how lucky I am to ride today’s stock bikes and how much better they are than what he had in the 1970s. I wasn’t around back then to form my own comparisons, but the 2006 KX450F is an amazing machine in stock condition. The bike comes with high-quality components like an aluminum skidplate and titanium footpegs and peg brackets.

The KXF flies straight and true  but it is a 450 and weights a claimed 220 pounds. Kawasaki still makes the KX250 for the FMX guys.
The KXF flies straight and true, but it is a 450 and weighs a claimed 220 pounds. Kawasaki still makes the KX250 for the FMX guys.

Like its little brother, the 450 can be modified at your dealer, as Kawasaki offers an options package that includes aluminum sprockets, a 20-inch front wheel, oversized handlebar clamp and optional fork and shock springs. With or without the additional modifications, Kawasaki has stepped up the plate in 2006 with a deliberate effort in the 450 class. No longer will dyed-in-the-wool Kawasaki guys be towed mercilessly up the long, rough straights of outdoor motocross tracks or have their KX250s drowned out in the confines of indoor stadiums by the roar of their competitors’ thumpers.

Michael Byrne has already put the new 450F to good use at the 2005 Maxxis U.S. Open of Supercross, grabbing second overall behind 2005 AMA Supercross champion Ricky Carmichael. Just wait until Bubba gets a hold of this thing for the 2006 outdoor series! With Kawasaki now on board, the 450cc 4-stroke ticket has been filled for 2006. It’s on now!

Let us know what you think about the 2006 Kawasaki KX450F in the MCUSA Forum.

MotorcycleUSA Staff