MXA’S 2006 KAWASAKI KX450F TEST

April 6, 2006
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One of the inherent problems with jumping on the bandwagon last is that almost everything that could be done has been done. The 450cc four-stroke technological hay wagon was almost around the bend before Kawasaki leapt on board. It’s been eight years since Yamaha single-handedly invented the modern four-stroke motocross bike in 1998. KTM got there five years ago, Honda four years ago, and Suzuki last year. Kawasaki is late to the party.

 

The downside of being last is that there are very few technically unique aspects left for the 2006 KX450F to tout. That said, the upside of not being the first to innovate is avoidance of the sociological phenomenon known as the “penalty of taking the lead.” Creative engineers, inventors and entrepreneurs pay a penalty for being first. There are two punishments for sailing uncharted waters: (1) Mistakes. The first designer suffers a litany of errors, trouble spots and bugaboos that could only be discovered by trial and error. Not so with the followersthey learn from the pioneer’s mistakes. (2) Consumer confidence. When Yamaha introduced the YZ400F, they had to spend millions of dollars convincing the American motorcycle racer that a four-stroke could win. That fact seems obvious today, but it wasn’t so in 1998.

 

The 2006 Kawasaki KX450F is built on the mistakes and hard work of the other four manufacturers. When done right, that is a good thing.

 

Q:WHY IS KAWASAKI SO LATE IN COMING TO THE PARTY?

 

A:It wasn’t their intention to be last. They had the KX450F ready for production last year. It would have hit the market months before the 2005 Suzuki RM-Z450 came on line. Woulda, coulda, shoulda. Unfortunately, the 2005 Kawasaki KX450F pre-pro suffered a very public, and very catastrophic, frame breakage at the All-Japan Motocross Championships just before the design was finalized.

 

The broken frame stopped all production plans. Although Kawasaki reportedly tried to retro-fix the D-tube, perimeter-style, aluminum framethey couldn’t. The 2005 bike was shelved. Thus, the 2006 Kawasaki KX450F is the second generation KX450F in only its first year.

 

Q:HOW DID KAWASAKI MAKE LEMONADE OUT OF LEMONS?

 

A:When the KX450F pre-pro failed and resisted efforts to be renovated, Kawasaki threw all the blueprints in the trash can and started over. Since there was no way to make the 2005 selling season, Kawasaki decided to set a target date of 2006 and start over from scratch.

 

According to Kawasaki sources, the 2005 pre-pro and the 2006 production bike share very few parts in common.

 

Q:IS THE KAWASAKI KX450F A KISSING COUSIN OF THE SUZUKI RM-Z450?

 

A:No. Emphatically no. We can understand why people might assume that the KX450F is a part of the Suzuki/Kawasaki alliance; after all, the 2006 RM-Z250 is the 2005 Kawasaki KX250F.

 

Not so with the KX450F. Suzuki and Kawasaki parted ways when the subject of a 450cc four-stroke came up for alliance approval. Both R&D departments agreed to disagree. Suzuki built the RM-Z450 on their own and came up smelling like a rose when the pre-pro 2005 KX450F broke in half.

 

The 2006 KX450F is a Kawasaki project from start to finish.

           

Q:WHAT ARE THE KEY INGREDIENTS OF THE KAWASAKI KX450F ENGINE?

 

A:For the techno-weenies, here are the numbers.

(1) Bore and stroke. It has a 96.0 x 62.1mm bore and stroke with a total displacement of 449cc.

(2) Valves. All four valves are titanium. The exhaust valves are 36mm in diameter, while the intakes are 31mm. Valve adjustment is by shim-under-bucket.

(3) Camshafts. The double overhead cam design uses two, forged, hollow-ground, billet-machined camshafts coated with a nitriting surface treatment.

(4) Piston. Kawasaki’s slipper-style piston uses two rings (one compression ring and one three-piece oil ring).

(5) Valve springs: Kawasaki uses double valve springs to fight high-rpm float.

(6) Gearbox. The KX450F has a four-speed transmission.

 

Q:HOW DOES THE 2006 KX450F REALLY RUN?

 

A:Every MXA test rider liked the KX450F engine. It wasn’t love at first sight, but just like a successful blind date, they found the KX450F powerband to be charming, usable, interesting and, most importantly, alluring. How does it run? It’s blessed with impressive throttle response off the bottom, a very torquey vibe through the midrange, and a relatively flat top-end. Most test riders likened it to an old-school four-stroke engine in that it revs at a pleasantly sedate pace, produces generous torque, and delivers a chuggy, thumper-style powerband that churns through the dirt.

 

It has a pleasant powerband. The initial power delivery is torquey. The initial rollout is the most impressive part of the power output. As the revs climb, the KX450F comes into a very meaty, manageable and usable midrange. It is in transition from low-to-mid that the KX450F does its best work. It doesn’t have a lot of top end, but because of its metered, modulated and timed powerband, it doesn’t need to go ballistic at the upper reaches.

 

In a nutshell, the Kawasaki KX450F engine is tractable, easy to use and old school.

 

Q:HOW FAST IS THE KX450F?

 

A:On the track, the KX450F has a drawn-out powerband that is most impressive in how fluid the power delivery is, not how forceful. For comparison purposes, the KX450F powerband is completely different from the RM-Z, CRF, SXF or YZ-F. It is chuggier, broader and slower revving than the competition.

 

Not a single MXA test rider thought that it was the fastest bike made, but all agreed that the powerband made it easy to go fast.

 

Q: DOES THE FOUR-SPEED TRANSMISSION HOLD THE KX450F BACK?

 

A: Yes. Thanks to abundant torque and a steady pull, the KX450F is capable of utilizing its four-speed gearbox much better than bikes with fluffier low-end power. That said, the four-speed KX450F is really a three-speed. How so? Not a single test rider ever used first gearexcept to weave his way through the pits. We used second on the start, second in most of the slow-speed corners and third as the bread-and-butter gear. Fourth gear was good for everything else.

 

Is a three-speed a handicap? Not in every case. Since the KX450F doesn’t have to be shifted very often, the racer gets maximum use of the KX’s torque curve. Although Kawasaki claims that the gearbox is close-ratio, in truth the ratios are fairly widely spaced (except for first-to-second). Each gear pulls a long waylong enough that you can hear the bikes next to you shifting while you are still pulling.

 

Q:  WOULD A FIVE-SPEED TRANNY HAVE BEEN BETTER?

 

A: Yes. You don’t have to be a marketing guru to realize that a four-speed tranny is a retailing boo-boo. Kawasaki’s engineers will probably wish that they had gone to a five-speed in the near future. Oh, don’t get us wrong, the MXA test riders could work with Kawasaki’s three-speed (plus one) gearbox, but the American consumer has displayed an appetite for five-speed trannies. So much so that the former four-speed YZ450F will be a five-speed in 2006. The dealers and customers demanded it. Not every bike sold is racedand trail riders, desert racers and cross-country riders want five-speeds.

 

Do we miss fifth gear on the Kawasaki? Yes. What is missing is a five-speeder’s ability to focus the power into bite-size chunks that a rider can choose to suit the situation at hand. On a five-speed, you could lug it in third or punch it in second. On a four-speed, you don’t have multiple options.

 

Q: HOW GOOD IS THE 2005 KX450F SUSPENSION?

 

A: We didn’t like it. Why sugarcoat it! We had nothing but trouble with the rear suspension of the KX450F. We could live with the 48mm Kayaba AOSS forks, but the rear shock had us scratching our heads (and soaking our sore backs).

 

Forks: Kawasaki opted for 48mm Kayaba AOSS forksbetter known as Showaba Twin-Chamber forks. The position-sensitive damping on Kayaba’s Air Oil Separate System (AOSS) forks means that the damping rates are dictated by the position of the fork’s piston inside the cartridge rod. In simple terms, the farther the piston moves down in the cartridge rod, the stiffer the damping. The AOSS’s progressive damping curve felt very light at initial stroke, remained light through the midstroke and then, suddenly, got much stiffer at the end of the stroke. That stiffness came on very quickly and was disconcerting. 

 

The average rider should start with the AOSS’s compression on 12 out and the rebound on ten out.

 

Shock: The shock wallows. Not just at speed, but in almost every circumstance. The compression damping is too light, and the rebound can’t handle the rapid pogoing of the back of the KX. This is the busiest rear suspension we have ridden since the twin-shock days. It never settles. We cranked in as much damping as we dared to try to put a lid on it.

 

Q: WHAT IS THE PROBLEM WITH THE KX450F’S REAR SUSPENSION?

 

A: In our opinion, the rising rate of the shock linkage is way off base. The initial stroke is too soft and it doesn’t ramp up enough at the end of the travel to properly control the oscillations of the rear end. The first clue to poor rising rate selection is when the bike wants to bottom in low-speed, high-load situations. These G-out conditions are solely controlled by rate change, since the slow shock speed doesn’t feed in much speed-sensitive damping. The KX450F needs more damping than it has to tame its movement.

 

The quick fix would be to go up on the shock spring rate. The stock spring is a 5.5 kg/mm, but you would probably need at least a 5.7 to hold it up under a load. Depending on your track, set the rebound on six clicks out, low-speed compression on four, and high-speed at 1-1/8 turns out.

 

Q: HOW DOES THE KX450F HANDLE?

 

A: We would be remiss if we didn’t say that Kawasaki is carving its own path when it comes to handling. The most evident handling characteristic of the 2006 Kawasakis is that they have a tendency to oversteer at turn-in (when the front wheel is first turned) and understeer from the center-out (where the actual direction change is made). That is not a handling scenario that would make any test rider’s wish list.

 

It should be noted that each KX model responds differently to the oversteer/understeer phenomenon. The now-defunct KX125 and new KX250F are the least affected by Kawasaki’s unique geometry, while the KX250 is most hampered by it. As for the KX450F, thanks to the abundant torque, it is possible to throttle steer the KX450F through a corner if the understeer gets too pronounced.

 

Q: IS THERE A TRICK TO DEALING WITH THE KX450F’S LOOSE FEEL?

 

A: Yes. First, get rid of the Dunlop 742F front tire. Although this is an oversized 90/100 front tire, it has none of the charms of the 739, 756 or 773. Second, get rid of the oversized 120/80 Dunlop 756 rear tire. You may be wondering what the rear tire has to do with the front end, but take our word for it, the large-profile 120 rear tire has a tendency to push the front tire through corners. In essence, the traction of the rear tire overpowers the front tire. Additionally, the big rear tire has a more planted feel, thanks to its bigger footprint, that lessens the roll rate of the chassis. We also believe that a smaller 110 rear tire would help the KX450F engine turn over a little fastergetting it through the gears with a snappier feel.

 

Q: WHAT DID WE HATE?

 

A: The hate list:

(1) Height: This is a big bike.

(2) Tires: Kawasaki went high-tech on tire sizes. They have a wide 120/80 on the rear and an equally wide 90/100 on the front. All good stuffbut not on the KX450F. Go with the best front tire for your track conditions and a 110-width rear.

(3) Handling: It’s odd.

(4) Brakes: We had to bleed the front brake at the second race. It lost lever pressure.

 

Q: WHAT DID WE LIKE?

 

A:  The like list:

(1) Power: Easy to use, broad and manageable. The KX450F offers a lot of powerband to work with, which translates into less shifting and more fun.

(2) Handlebars: Renthals’nuff said.

(3) Brake rotors: Borrowing a page from KTM, the brake rotors on the 2006 KX250 have been cauliflowered to help distribute heat more evenly and to make them self-cleaning.

(4) Starting: No hassles.

(5) Radiators: At first glance, the KX450F radiators look inadequate for the job, but the new high-efficiency Denso radiators have more fins in a densely packed radiator core for better cooling.

(6) Titanium: We aren’t big fans of titanium footpegs, because the weight they save is so low on the frame that it is almost meaningless, but we did like Kawasaki’s tapered titanium exhaust system. Very sano.

(7) Shifting: When you shift on the torque curve, the KX-F gearbox and clutch work very well.

 

Q: WHAT DO WE REALLY THINK?

 

A: Loved the engine. Loved the clutch. Loved the shifting. Loved the powerband. Loved the handlebars. Loved the exhaust pipe. Loved the radiators. Loved the look. Unfortunately, we didn’t love the bike because of its idiosyncratic rear suspension.

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