The Motorbike Archives

Of course, Kawasaki's newest 125cc motocrosser really isn't quite that radical, but it does buck the trend toward ultra-tractable performance profiles among the newest Japanese 125s. The current offerings from Suzuki and Honda, for example,- emphasize a flexible powerband and rough-track competence over sheer rock-throwing horsepower and berm-blasting potential.

Suzuki and Honda both build their 125s to favor long Sunday motos run on natural-terrain tracks that have been thrashed by hundreds of bikes all afternoon. And, in all truthfulness, even Kawasaki has mellowed the KX125 since last year to make it more suitable for this kind of racing. But despite those efforts, the KX still seems like a Friday Nite Special by comparison. The relatively smooth, manicured tracks used for night motocross are the A5's stomping grounds. Nasty whoops and difficult off-camber turns prevent it from running fast and loose. It would rather spin its rear wheel enthusiastically and screech around a nice smooth track.

While the KX125 might be one of the last of the high-strung 125cc motocrossers, it's far from unrefined. Kawasaki has taken great pains to make it much better than ever and competitive with its rivals. As Suzuki's RM125N draws on the RM250N, the 125 Kaw borrowed most of its refinements from the KX250; but unlike those two Suzukis, oddly enough, the personalities of the two Kawasaki motocrossers remain vastly different.

The most notable transformation in the KX125 has occurred in the engine room. The motor still relishes lots of revs and delivers most of its horsepower at high rpm, but the transition into the powerband has been made smoother. The A5 engine still appreciates a quick fan of the clutch in many cornering situations to uncork its power potential when the rear wheel is bogged down, but forward thrust no longer materializes with such explosive suddenness. You can dial on the power with the assurance that the engine will not unleash all of its fury at once.

The A5 owes much of its newfound tractability to its crankshaft flywheels. They've been enlarged 3mm in diameter to increase the flywheel effect, which is the same strategy that worked a similar transformation on this year's KX250. The remainder of the small-bore KX's new engine personality has been produced by fine-tuning. The larger airbox from the KX250 is fitted and the dimensions of the expansion chamber have been altered subtly to enhance the engine's transition into the powerband. The 32mm Mikuni carburetor also has been comprehensively rejetted to mate with the improved tuning specs.

New thinking in the A5's gearbox further soothes the engine's power delivery. First, second and third gear each have been made fractionally taller, and the rear-wheel sprocket is four teeth smaller as well. This combination of gearing changes makes first gear 16-percent taller while sixth gear is five-percent taller. These new ratios help the rear wheel to hook up better than last year and lend the A5 the sort of controllable, divot-digging power the A4 lacked.

Friendly or not, horsepower can't do you much good if the rear wheel spends too much time in the air. And last year's KX125 often violated this cardinal rule of motocross whenever the terrain turned cobby, largely because it had the shortest suspension travel of any Japanese 125 MXer. So to improve that situation, Kawasaki has given the KX125 longer legs.

In the rear, the A5 has been updated by lifting a few tricks from the KX250. The gold-anodized swingarm, for instance, is identical to the 250's and it's 1.8 inches longer than before between the swingarm pivot and the lower shock mounts. This modification alone accounts for most of the A5's 2.2-inch longer wheelbase. Furthermore, the upper shock mounts were dropped several inches lower on the frame's rear diagonal support tubes to give the shocks a more-radical lay-down position. And just like the KX250, portions of the 125's frame beneath the seat were gusseted and a horizontal support bar added to withstand the increased stresses of the new shock-mounting arrangement. The shocks themselves maintain the same eye-to-eye length as before, but revised internals permit 13mm more piston travel than before. The combination of the new shocks and their more-radically inclined mounting has yielded 1.2 inches more rear suspension travel.

The Kayaba air/spring fork also has been updated to complement the rear suspension with the addition of just over a half-inch of new travel. But the same amount of tube/slider overlap as before has been maintained, so no front-end rigidity was sacrificed. Kawasaki apparently knows that a strong front end makes an undeniable contribution to good handling, because there now are double pinch bolts in the upper triple clamp replacing the A4's single bolts.

As might be expected, these suspension changes have altered the KX125's steering geometry. Raising the rear end more than the front to accommodate the longer travel has tucked in the steering head angle a full degree and reduced the trail by 0.2-inch. That results in slightly quicker steering that calls for a little less effort on the part of the rider. And that's a benefit, for it helps compensate for the agility the KX lost through its dramatic increase in wheelbase.

On the track, the Kawasaki's suspension doesn't smother the bumps quite like that of a Suzuki or a Husqvarna. As long as the track doesn't get too cobby, though, the A5 keeps its wheels on the ground nicely. But because the bike has shorter suspension strokes than its competition, Kawasaki had to calibrate the springing and damping rates a few percentage points stiffer. The suspension works well, but it can be just a bit harsh on abrupt, sharp bumps.

Discussing the Kawasaki's suspension in terms of raw travel, however, can be misleading. Suzuki, for instance, builds a lot of droop into the RM125N's suspension, and once you sit on one, it settles quite a bit. Consequently, the RM's wheels follow the terrain more effectively because they can drop into holes without dragging the rest of the bike in after them. Without the same amount of droop, the Kawasaki lacks the same overall suspension travel, but it does have almost as much compression stroke. The entire KX125 drops into some holes because it lacks that extra bit of wheel extension. But on the plus side, the Kaw's firmer suspension rates keep it from pitching back and forth as much as a Suzuki, minimizing the drastic steering geometry changes that can make cornering an unpredictable proposition.

Kawasaki's well-orchestrated program of engine and suspension changes goes a long way toward making the KX125 a better Sunday-afternoon racer than ever before. The long wheelbase helps the bike track impeccably on long, rough straightaways, while the recalibration of the engine and gearbox transmits power to the ground more effectively.

Despite its improved manners when the going gets rough, the KX125 is still best-suited to relatively smooth and featureless terrain. To make the bike go the fastest, you have to be sure that the rear wheel is spending as much time on the ground as possible while the engine is delivering power in sustained, high-rpm charges. The Kawasaki can't keep up with an RM125N, for example, if it's leaping around in the bumps where power can be applied only in short bursts. It's far better to find a track where you can hold the throttle wide open. This is one racer that's happiest when you keep its throttle nailed to the stops while bouncing off every available berm like you were playing moto-pinball.

If you so desire, you can use the Kawasaki's powerful, progressive brakes to dive underneath your competitor while braking. The full-floating rear brake will kick the rear wheel out controllably to start the bike pivoting, and the steering geometry cooperates by making the little Green Meanie go where you aim it. The front tire grips well, and the new short tank (complemented by 250-type handlebars) helps get your weight forward to improve front-wheel traction.

But accurate steering or not, the KX's semi-pipey engine performance keeps you from slowing down in a corner any more than is absolutely necessary. That's because short, wheel-spinning bursts of high-rpm power are not ideal for accelerating from low speeds. You're better off to take the outside line, where you can maintain more momentum.

This means that even though Kawasaki took much the same approach to building its 125cc motocrosser as its 250, the 125 is not a 250-clone. The KX250 has a broad powerband and a smooth power curve, while the 125 is rpm-city all the way. Give it a mildly bumpy track and a rider who has forgotten how to shut the throttle, and the KX125 will charge from corner to corner like some sort of berm-seeking missile.

In a curious way, the Kawasaki's high-strung temperament makes it a lot more fun to ride than many other 125s, even though racers have complained for years that pipey bikes are hard to ride well. But there's no denying the sense of satisfaction you get from holding a 125 wide-open every second as you fling it recklessly around the track. Even if your lap times aren't equal to those of some other one-two-fives, you walk away from the KX feeling like… well, like you really used it up.

That's why the Kawasaki is such a fine Friday Nite Special. Short motos and non-punishing tracks—whether they are a Friday-night or a Sunday-morning phenomenon—are meant to deliver ego-boosting excitement. And boosting your ego with sustained rushes of high-rpm horsepower is one task the KX125 is built for.

RIDE REVIEW

Every time I finish a ride on the KX125, I climb off of it fully satisfied that I've used up everything it has to offer. I load it back into the van feeling that it's been "rode hard and put away wet," as the cowboy expression goes.►