Memorable Motorcycles KDX 175

June 3, 2009
Frank Melling
Frank Melling
Contributing Editor| Articles|RSS

Our Memorable Motorcycles expert, Frank Melling also is the organizer of the British vintage motorcycle extravaganza known as Thundersprint. Melling began riding five decades ago and remains as much in love with motorcycles as when he drove his first bike into a cow shed wall aged ten. In the last 50 years, Melling has competed in every form of motorcycle sport and now declares himself to be too old to grow up and be sensible.

Kawasaki KDX 175
Perfect the KDX isn’t, but the best value-for-money package available at the time it certainly was.

I always tried to be scrupulously honest as a journalist but in this evaluation of Kawasaki’s lovely little KDX 175, written in 1981, what would have made the story really interesting is what was left out. At the time I wrote this story, I was being particularly well treated by Kawasaki and I had just collected a brand-new KDX250 enduro bike from Doug Hacking Motorcycles, who were one of Europe’s biggest off-road Kawasaki dealers.

The bike had come directly from Kawasaki, along with a generous spares’ allowance, for me to ride in British Championship enduros and wherever else took my fancy. The same situation is still used today with journalists who are good on a bike receiving a lot of encouragement from a manufacturer to see the virtues of their brand – and to express them in print! The difference was that 28 years ago, there were far fewer competent racer/journalists, so if you were a top 20 British Championship rider, which I was, there were really good incentives available.

So here is the part that I didn’t write. The story came directly from a senior, an extremely senior, person within Kawasaki’s racing division and I will leave it up to you to decide whether it is true – or not. It is, however, exactly as it was told to me.

Kawasaki was the first manufacturer to use a mechanical leverage to provide rising rate rear suspension in a production motorcycle. In simple terms, rising rate suspension is where the rear shock is not compressed consistently so that it gives initially soft compression which then becomes harder towards the end of the travel. This had been a holy grail of suspension designers right from the early 1920s and had been achieved by having two, or more, sets of springs on one suspension device. The first, soft ones, provided the initial travel and then they combined with a stiffer second set to deal with bigger loadings.

Kawasaki KDX 175
Kawasaki’s goal was to bring their Uni-Trac to the public and soften the traditional harsh ride.

The problem was that multi-rate springs did not provide the linear rising rate which the designers sought – and riders begged for. The Uni-Trac, with its purely mechanical compression of the rear shock, promised to be the solution. For an off-road bike, this was a dream. The rider could float along with the rear wheel maintaining grip and the front end compressed – typically when braking or going downhill – and the stiffer element of the rear suspension would give stability over big jumps. Keeping the rear wheel constantly in touch with the ground also vastly helped traction under acceleration and braking.

With Kawasaki’s design, this was achieved by making the shock move not directly by pushing it from the swinging-arm but rather by making the swinging-arm move a lever which then compressed the shock. If the engineers got their maths right, the mechanical ratios could be designed such that initially the shock only moved a little bit, and so the suspension was soft, and then was made to accelerate so that the shock action became stiff towards the end of its stroke. So far, so good – primarily because all engineers love math, and the more complex the better.

At the time, all off-road Kawasakis were manufactured in Lincoln, Nebraska. When the engineering drawings arrived from Japan for the new motocross machines a zealous, enthusiastic American engineer saw that his Japanese colleagues seemed to have made a fundamental mistake. They had designed the rocker arms for the rear suspension so that the travel was inconsistent. In fact, they had built rising rate suspension. Now, how dumb was that?

So, the legend has it, the mistake was corrected and all the bikes now had FALLING rate rear suspension which actually worked completely contrary to what was intended. It’s easy to sneer at this mistake but you have to understand that a lot less was known about engineering almost 30 years ago – and the lines of communication between Japan and the US were vastly less sophisticated than they are today.

The only bike which escaped the redesign was the KDX 175 which, from the outset, had been conceived with neutral suspension. In the little enduro bike’s case, the Uni-Trac rocker-arm suspension was purely a marketing gimmick since the shock had a linear movement directly related to the rear wheel. Ironically, because the KDX was left out of its bigger brother’s birthday treat it worked – whilst the cleverer systems on the motocross bikes most certainly didn’t!

Kawasaki KDX 175
At 228 lbs the little KDX is not a superlight 175, in fact it is almost in the 250cc weight range. However, once on the move it feels feather-light.

Although the rising rate suspension design didn’t help the bike, the by product of using the concept did. Although a big lump for a 175, the mass centralization meant that the KDX was very stable and ultra-forgiving, both endearing traits for sportsman riders.

There is a final twist to this story. The truly best suspension of the day was an extremely sophisticated twin shock design used by Husqvarna and manufactured by Ohlins. This was simply light years ahead of anything from Kawasaki but looked old fashioned and dated. Despite its qualities, riders wanted the biggest-latest-cleverest-trickest suspension and Husqvarna had to abandon the twin shock design.

The story also reveals what simple creatures we were 30 years ago. Even good expert riders like me did very little with the bike’s suspension and certainly no Sportsman competitor would have the slightest interest in modifying a rear shock. We rode what the manufacturers gave us and were either annoyed, frustrated or grateful. But we got on the bike, nailed the throttle and rode: that was it! The thought of employing the current sophisticated suspension tuning techniques used by modern riders would have not only been inconceivable but, in truth, of very little interest either! Truly, we were simple souls!

So here is the original story from 1981 of one of the nicest enduro bikes of its generation – and one which helped a lot of amateur riders fill their trophy shelves.

Kawasaki KDX175 Uni-Trac – Original Story

For a bike which arrived so late in the season – the first of the little Kawasakis did not go on sale until the summer of 1980 – the KDX did amazingly well in its first year. It was immediately greeted as being the definitive answer to the sportsman rider’s prayer.

Kawasaki KDX 175
The KDX was forgiving of rider mistakes which more than made up for some of the bike’s other short comings.

The reasons for this were immediately clear to anyone who rode the bike. One could make the most dreadful mistakes and the KDX would sort them out – a trait which more than made up for the bike’s lack of speed. Most enduro riders are far more interested in staying on board their bike than getting the fastest time on the motocross special test!

For the 1981 season Kawasaki followed up the success of the original KDX175 with a new bike whose power had been boosted by a claimed 4 hp. This makes the new KDX an even more attractive proposition and puts it embarrassingly close to some of the weaker European manufacturers.

I feel sure that Kawasaki realize they cannot produce a bike which is the equal of a KTM or SWM in ISDT competition, but what they can do is make a motorcycle on which a vast number of riders can motor along very quickly.

The original KDX was low and had an easy, neutral handling which made it extremely hard to crash, and the new models seem to be built in the same vein. They are not going to be the choice of the British Trophy Team, but they will win a lot of medals for lesser riders. A case of losing the battle and winning the war, at least in terms of Kawasaki’s profitability.

Perfect the KDX isn’t, but the best value-for-money package available today it certainly is. With a retail selling price of only $1450, and handling as good as any enduro machine I have ever ridden, the KDX is clearly the best buy in the market place for everyone except a potential class winner in a National enduro.

Kawasaki KDX 175
The long wheelbase and heavy front end gives the bike more stability in a straight line with the Uni-Trac to credit for pulling it all together.

The KDX is not – and does not claim to be – an ISDT bike. The motor lacks the arm-wrenching surge of a really fierce ISDT motor hitting the powerband and the chassis is also devoid of a few of the accoutrements which grace a serious six-days’ bike. For example, there is no speedometer, center stand or chain guard. In return for these weak areas the KDX offers an ease of riding and stability which most riders will welcome with delight, for there has not been an easier bike to ride since the days of the early Suzuki PE250s.

The focal point of the bike is the rear suspension. Road riders, unused as yet to unconventional methods of rear suspension, peer inquisitively beneath the rear mudguard to see just what does hold the wheel in.

Not that there is a lot to see. Two long steel rods push up from the swinging arm on to a rocker which compresses the large damper hung vertically behind the swinging arm. This system offers a number of advantages over conventional systems, including Yamaha’s monoshock. First and foremost, the center of gravity is dramatically lowered. At 228 lbs the little KDX is not a superlight 175, in fact it is almost in the 250cc weight range. However, once on the move it feels feather-light; much more so than even sophisticated opposition like the 175 KTM, which feels light when static but which rides like a 400cc.

Using the Uni-Trac the bike can also be made very slim in the saddle, since there is no need for a bulbous sub-frame to accommodate twin rear dampers. Again, this makes the bike feel light and easy to handle.

Finally, production bikes being what they are, it is much easier to get one damper working as the designer intended than two. On a factory bike, the ride of a twin-damper machine will be just as good as the Kawasaki’s system, but few enduro riders ever change their rear suspension and fewer still will modify their bikes from meeting to meeting. The KDX works well just as it leaves the showroom floor and this is what most riders want.

Kawasaki KDX 175
With plenty of power through corners the KDX 175 performed more like a 4-stroke then a 2-stroke.

In practice the KDX rear end performs really well. The bike is at its best when ridden with the rider seated – an essential and welcome trait in any enduro bike – and in this manner the rear wheel transmits plenty of feeling but no shock. Thus, sliding the KDX on a camber is a safe and predictable exercise because one can feel just what is happening to the rear end, whilst leaping the bike off ledges can be done with confidence, safe in the knowledge that the rear wheel is not going to clang to a halt at full compression.

The amount of drive the rear wheel finds is exceptional. The way in which the power could be really whacked on hard whilst still cornering was reminiscent of the behaviour of a 4-stroke rather than a 175 2-stroke. When the rear wheel did step out it did so predictably and without malice. No doubt it is possible to crash a KDX, but one would have to try very hard to do so.

The amount of drive which the bike does find is surprising in view of its rather unusual dimensions. The Uni-Trac rear end demands that a long swinging arm is used, which results in a 57.5-inch wheelbase. Such a wheelbase naturally gives excellent stability in a straight line, but tends not to give such good drive on a 175. That it does is a credit to the Uni-Trac system.

A further problem with a long wheelbase is that the bike tends to become sluggish on corners. Kawasaki has solved this problem by tucking the front end in with a very steep 62 degree head angle. Unconventional though this system may be, it works very well in practice, giving excellent handling characteristics under all conditions. The only criticism I have heard made of the bike is that it is front end heavy. Personally I like this, since full power can be used with confidence at all times – including up killer steep hills. Bikes which loop at the slightest provocation are of no interest to me in enduros.

The little Kawasaki motor complements the rest of the bike very well. It is not an outstanding unit, but produces plenty of power throughout the range and is very forgiving. Thanks to the Uni-Trac rear end the power is converted into drive rather than wheelspin, so in practice the KDX will stay with any of the other Japanese 175s. However, you are clearly not going to burn off an SWM or KTM on forestry tracks.

Kawasaki KDX 175
Full power from the KDX 175’s 2-stroke mill could be used with confidence at all times – including steep hills.

Having acknowledged this, the KDX has much to commend it to sportsman riders. It starts easily and both clutch and gearbox are faultless. Kawasaki dealers are also reporting minimal sales of spares, which is encouraging. One point to watch is the electrofusion barrel, which cannot be rebored. Provided with clean air this system is first class, but air filter maintenance needs to be impeccable.

Whilst keeping the weight down, the KDX’s miniscule 5-inch brakes are a little too small for my taste. They work satisfactorily, but require too much pressure to be comfortable. On forestry tracks I would prefer anchors with more potency.

The running gear on the KDX is excellent. Like all Kawasakis the bikes are very well finished with good quality paintwork – by Japanese standards – and well-made plastic components. Kawasaki deserves criticism for not providing the bike with a speedometer or metal tank so that it is road legal. It is no excuse at all to say that the bikes are to be used only in off-road events, since they know full well that there are no events in which the KDX can be used competitively which at the same time do not demand that the machine be road legal. Honda, Suzuki and Yamaha all make their bikes at least almost road legal so that the rider has a 99% chance of using the bike for its intended purpose and still stay within the law, but Kawasaki have taken the cheap way out – a policy which does them no credit at all.

Our test bike was provided by Manchester enduro expert Gethin Evans, who also brought his ‘spare’ 175 Suzuki along for comparison. The KDX is best summed up by saying that we fought all day long for who would ride it. It is safe, fast and predictable and the sort of bike on which I would happily race anywhere.