Japanese 250mx Comparison
JAPANESE 250MX COMPARISON
A WISE OLD motocrosser once said, "Nothing that remains the same for very long, remains for very long." And while it was certainly true when he said it, it is even more true in today's marketplace of blitz-like change and overnight sensationalism. The Europeans have brought much change to the sport of motocross, a sport they introduced to this country and which they still dominate whenever and wherever present. The Japanese had to play catch-up and they had to play it fast. The first Japanese "motocross" machine as we know them today was introduced in 1970 as the Yamaha DT1-MX. In six short years Japan has come from total anonymity in motocross competition to virtual equality with its more experienced but less highly financed European counterpart. Thus, in this small span of time, the four major Japanese firms have done what it has taken other corporations decades to do. They certainly have not remained the same, which has pretty much assured them that they will remain.
• So, while Japan has been busy keep ing pace with the rest of the motocross world, how has the competition faired between the country's own four top brands? That's just what we aimed to find out by initiating this four-way comparison of the Honda, Kawasaki, Suzuki and Yamaha 250 MXers.
ABOUT THE PROCEDURE
First, of course, the machines were called in from their various manufactur ers. Yamaha International sent us its latest 250 YZ, American Honda the new red-framed CR250M2, and U.S. Suzuki uncrated a new RM250 for our pleasure. Kawaski Motor Corp. was unable to provide us with a test bike, so we obtained a new KX250 through the courtesy of Tom Orlando at Champion Motorcycles in Costa Mesa, Calif. Tom runs a tidy shop and can meet your needs for Kawasakis, as well as for several more exotic motorcycle lines such as BMW, Ducati, Laverda and MV Agusta.
With the machines ready and waiting in the CYCLE WORLD shop, measure ments were taken for the data panels. The bikes were also weighed and final prep was performed for a two-day out ing at Indian Dunes.
Recent rains made the International course at Indian Dunes unridable, but the owners had already taken care of that by bulldozing a new track in the quarter-mile-wide sandwash area just be hind it. Our first day was spent getting much photography done. . .doing berm shots, wheelies and powerslides all for the benefit of our shutter freaks. Then, toward the end of the day, we com bined part of the new sand track with a ridable section of the International course and literally created our own virgin motocross track. By now, all three riders were familiar with the machines, so after a few warm-up laps to reacquaint themselves with the var ious mounts, lap times were taken.
An overnight stay at a local inn, then back out to the Dunes we went. Close inspection told us that the moist sand we had been running in had hardly affected the air filter elements, so we left them alone. The chains, however, received proper maintenance. With the chains doused in Bel-Ray chain lube, and liberal amounts of WD-40 applied to all pivot areas-such as brake pedals, footpegs and kickstarters-the machines were ready to go. We topped the tanks off (all of the bikes were run on Bel-Ray MC-! at 50:1, except for the Suzuki whose distributor insisted that we use only Castrol R mixed at 20:1) and out we went for more photography on the Shadow Glen track. Shadow Glen was in perfect condition. Here, recent rains had soaked deeply into the ground, leaving only a light film of mud on the track. The Indian Dunes grader whisked that off and we were left with almost pic ture-perfect loam.
After we tired the photographers out, lap times were again taken. While at the Dunes, it is usually our custom to time the bikes over a 100 to 150-yardlong section of whoop-de-doos, but the rains had obliterated them. The rains had, however, raised the stream at the Dunes to a relatively high level, and, while all of the machines crossed the stream several times without drowning out, it should be pointed out that after studying the location of the electrical components and airbox design, we feel that the Suzuki and Honda would be the most difficult of the four to drown. A weekend passed, during which time the machines were thoroughly ser viced. The next week we went out to both Saddleback and Escape Country, two tracks much nearer our Newport Beach offices than Indian Dunes had been. Here, we encountered problems. Weekend races had cut devastating footdeep ruts in the softened track surfaces. Overnight winds had dried the clay surfaces rock hard, making traction non existent at best. Corners had to be approached sitting down, with both feet raised in order to prevent ankle-tweak ing snags in the deep ruts. In some corners, the footpegs were hanging up on the ruts. Useful lap times were impossible, but we rode these tracks anyway just to see what they were like; while we learned little about handling due to the heavily reduced speeds neces sitated by the track conditions, we came away with some very interesting obser vations about engine tractability and line-holding capabilities of the various steering geometries represented.
Finally, the bikes were given a thor ough going-over and trucked, first to Webco for a run on its sophisticated Schenck engine dyno, and then to Num ber One Products, where the suspension components were dyno-tested to help us better understand why they had per formed as they did.
The following is a result of what we learned about the four Japanese 250 motocrossers! Which ones are good, which ones are better and which one is best.
HONDA CR250M2
Attractively styled in Honda racing red with black trim, the CR250 wins our vote as the best looking of the machines tested. It is powered by a piston-port two-stroke engine much like the Kawasaki's. The Honda is unique among the test bikes in that it uses a Keihin carburetor instead of the more popular Mikuni. The Honda was, along with the Yamaha, perfectly jetted. We didn't have to mess at all with either machine.
The chassis on the CR is a single downtube chrome-moly unit. It proved to be quite strong throughout our test ing. The swinging arm is also chrome moly, but it did not display the rock steadiness of the frame. Whenever the limits of the forward-mounted Showa
shock absorbers were reached, the swing ing arm began absorbing the stress de livered by the race track. Since it could not release the built-up stress out the front end into the sturdy frame, it let it go back the way it came, making the rear end hop and pitch when track situations got severe.
It is interesting to note that the Showa shock absorbers are of the gasemulsion variety. Whereas most gaspressurized shocks have a floating mem brane to separate the oil from the gas, some units, like Girlings and the latest Bilsteins, depend on an emulsification of the oil and gas to provide their damping. It should be pointed out, however, that the Honda's shocks fell far short of the performance of both the Girlings and Bilsteins.
HONDA
KAWASAKI
The CR brake hubs house the best brakes to be found among these bikes. They were powerful, easy to control and completely impervious to water. Laced to each hub is a D.I.D. rim, which we feel are just about the best thing going. Bridgestone tires are found on the red racer. . .3.00-21 up front and one of the new 4.50-18 variable pitch (see Honda CR125M2 test in last month’s CW) knobbies in back. Bright red fenders, black anodized handlebars and a comfortable seat round out the package.
KAWASAKI KX250
The engine in the KX250 is possibly one of the most versatile Japanese motocross mills to be found. Fed by a 34mm Mikuni, the powerplant is housed in a single-downtube mild steel frame. Air filtration is by oil-wetted foam, as on all the other bikes. Kayaba gas/oil shocks are mounted in back in a halfcantilevered, half-forward-mount position.
The folks at the Big K have made an error, we feel, in the styling department. Last year’s KX was done in traditional Kawasaki racing green with white fenders and accents. This year the bike is metal-flake green with black fenders. A set of white fenders might help the looks. But despite their color, the fenders on the KX are excellent and not the kind that you would normally discard.
Dunlop provides the tires on this one. The 3.00-21 front tire did not prove to be anywhere near as treacherous as it was on the Yamaha, and the 4.60-18 rear knobby worked best when the track had some moisture in it. Standard left-side shift engages and disengages the gears in the five-speed transmission. The KX’s brakes are also very powerful, although not the equal of the Honda’s. D.I.D. rims are used here also. The Kawasaki is the only one of the machines to come equipped with a down-pipe.
SUZUKI RM250
One of the most dramatic changes in the motocross world was Suzuki’s move from TM-series motocrossers to the RM line. The new bikes are replicas of the Grand Prix Works bikes, with production considerations factored in. Unique in its use of case-reed induction, the RM250’s engine is designed to yield greater power over a longer range than other types of two-stroke engines.
To keep things in line, Suzuki utilizes a chrome-moly frame and swinging arm, along with Kayaba gas/oil shocks built to Suzuki’s specs and long-travel forks with an offset front axle. Paint styling easily identifies the machine as a Suzuki. Attractive yellow covers the tank, plastic fenders and side panels.
HONDA
KAWASAKI
The RM is the only machine that does not come with D.I.D.s. Takasago provides the rims for this 250. While they are very light and do not have mud-collecting ridges, they do not have the strength of the others. Bridgestone tires are also found on the RM, although the variable pitch design is reserved only for the Honda.
Suzuki has fitted its latest motocrosser with a number of minute touches typical of details that only the Japanese look after. Rubber grit covers are found on the brake and clutch levers, as well as on the rear brake cable and the kickstart pivot point. The rear wheel can be removed, but the chain adjusters stay bolted in place to make refitting of the wheel much easier and readjustment of the chain unnecessary.
YAMAHA YZ250
Though the Yamaha is also styled in yellow, it is easily discerned from the Suzuki by its unique black accent stripe on the fuel tank. This year, Yamaha has used basically the same motor as last year, changing only the ignition for greater reliability and the exhaust for lower noise level. What makes the 1976 model faster than those that came before it is the suspension.
Up front, a pair of patented air forks, built by Kayaba, soak up punishment better than anything that Japan has ever offered. The forks are unique in that each leg has an accumulator bottle on top. Inside the bottle is a free-floating piston with air chambers both above and below it. The lower chamber compresses as the fork compresses and the oil rises within the fork leg. Since compressing air is not truly progressive, in a normal air fork (one with air caps only) the final few inches of movement can be virtually useless. While the first few inches may compress at a 25 lb./in. rate, the last few might require as much as 300 lb./in. What Yamaha’s forks do then, is allow you to set each air chamber (upper and lower) to a different pressure. When the pressure in the lower chamber builds sufficiently during fork travel, the free-floating piston moves, volume in the fork leg is increased and fork action again becomes progressive. The forks are highly adjustable, but we recommend that you start with settings of 27-29 psi in the lower chamber and 52-54 psi up top. Oil level should be 175mm from the top of the fork leg at full extension. This converts to approximately 415cc per side.
In the rear, the Monoshock has received a new, longer shaft that increases measurable axle travel to a touch over seven inches. Oil volume is up by nearly 10 percent, while gas pressure is down slightly, reducing some of the preload that made previous models hop mercilessly over smaller obstacles.
Brakes on the YZ are both half-width affairs, but different as night and day. The front anchor is almost legendary as one of the best around. It didn’t let us down. The rear brake has a reputation for over-sensitivity that goes way back to the first DTI-MX. It didn’t do anything to alter its reputation, either. Tires are by Dunlop and were Yamaha’s downfall in this test.
SCORING
As has been our practice in the past, comparison tests are decided on the basis of points accumulated. Less significant features or performances, such as suggested retail price or drag race showings, are scored on a simple 4-3-2-1 from the best to the worst. Lap times, because they are, after all, much more important to a motocrosser’s sole functions, are scored on a 12-9-Ó-3 basis. Bonus points are awarded for features on a machine that we feel are aboveaverage. A quick example would be loose spokes. On new machines you expect that the spokes will loosen up a few times before they bed themselves in. We did not give any penalty points for loose spokes because such things are about par for new motocrossers. But the rear spokes on' the Honda and Suzuki refused to loosen, regardless of the pounding dished out. This is aboveaverage performance, deserving of bonus points. The Honda is in an unfortunate situation. While it came in third in our comparison test, changing a few of the bike’s features would easily put it up near the first two machines. Suspension is the bike’s weak link. Fork action is harsh. It loosens up after a while, much as our CR125M2’s did last month, but it still doesn’t come up to par with the Yamaha’s or Suzuki’s. Measurable fork travel is a lowly 6.75 in. Even the new 125 Honda has more travel than that. The front end on the 250 is seriously outdated. However, with 4.75 in. of slider-to-stanchion engagement, a good fork kit can bring the travel close to eight inches without too much trouble. Number One Products makes such a kit, as does S&W.
Penalty points were handed out for
sub-par features such as the Yamaha’s soft handlebars or air filters that were troublesome to service or difficult to achieve a good seal with.
PERFORMANCE: HOW AND WHY
HONDA CR250M2
Shock absorber performance is even worse. While in appearance the shocks may look identical to those on the new red 125 in last month’s issue, their characteristics both on the track and at the shock dyno told us that they are nowhere near the same. Excessively harsh action in the rear not only makes for a jarring ride, but also induces swinging arm flex. Eventually the swinging arm bushings will have to be replaced, but we didn’t have our machine long enough to wear the original set out. The pitching in the back end was caused by excessive compression resistance attributable to high spring preload and insufficient return damping for the
strength of the spring. The Honda lost a lot of time getting into rough corners and going down heavily potholed straights. It lands stiffly but controllably off most jumps.
While it was no fun stuffing the CR into rough corners, it was an absolute gas through smooth ones. The best brakes by far were found on the Honda. And it steers like a Maico. As we raced around against each other and against anyone else who happened to be on the tracks at the time, it was easy to outbrake the competition into a corner and then beat them through it by taking the inside line and just laying it over and gassing it. The Bridgestone tires are super. Engine power is quick, but controllable.
If you go by feel, you might think that the Honda does not possess as much horsepower as the other three
bikes, but the dyno shows us that that isn’t so. What happens is that, after reaching maximum horsepower, the Honda shuts the door on the revs rather quickly, while the others will rev out farther, though not producing any more power. To go fast, you must shift the Honda immediately after reaching peak power. If you have to blast down a short 40-yard straight and the engine peaks after 30 yards, upshift for those last 10 yards or the CR will stop accelerating. When this occurs, the other three bikes will continue to rev past their power peaks and ease by the Honda. It means that you might have to shift the Honda a few more times per lap in order to go just as fast, but that’s not a big hassle since the CR’s tranny is very slick in operation and not tiring to use at all.
The easy cure for the Honda’s suso pension woes is a fork kit as mentioned, and shorter, slightly softer rear springs. The gas preload in the shocks is adjustable, but you need a dealer to work on them. You won’t find many service stations that carry 225 psi in their air lines. If you decide that you want to slightly depressurize the shocks yourself, then turn them upside down and compress them a few times, then let them sit that way for a few minutes before you slowly bleed them. Bleeding the pressure out of the shocks while in the standard position will squirt a jet of oil halfway across town.
If you don’t mind a little investment, then we suggest that you eliminate the stock rear dampers altogether. Works Performance shocks, gas Girlings, Bilsteins or the new freon S&Ws make a nice replacement. With just these few modifications, you can be ready to go
hunting the hot RM Suzukis.
KAWASAKI KX250
The new KX suffers from suspension problems, just like the Honda does, but it also suffers from an insufficiently rigid frame that flexes from the pounding that the inadequate suspension delivers at racing speeds.
Suspension-wise, front end performance lacks both proper compression and rebound damping. The front wheel pogos over potholes and stutter bumps.
HONDA
CR250
$1325
KAWASAKI
KX250
$1216
It also twitches from side to side. This is normally an indication of either fork or frame flex at the steering head. The forks on the KX are strong, so the frame is the culprit. Further gusseting of the steering head may cure the problem, or it may just send stress forces deeper into the frame until they find another weak point at which to relieve themselves. If the rest of the frame is up to snuff, then the problem will be cured with the gusseting. Of course, a proper fork kit would alleviate much of the stress being delivered to the frame, making a cure that much simpler.
Fork travel is good at 7.5 in. and could easily be increased another threequarters of an inch without reducing engagement to a dangerous level. The Kayaba gas shocks in the rear travel only 3.75 in., but their position yields just over six inches of travel at the axle. On the dyno we found these shocks to have identical damping characteristics to the RM shocks and the Yamaha TT500 dampers. However, while the Suzuki’s shocks are perfectly suited to their application, the Kawasaki’s forwardmount is not as severe. With this lesser mechanical advantage, the compression damping proves to be too high. To top this off, the spring rate is too light. This totals up to a shock that kicks up in the back end, yet can be easily bottomed when the pressure to it is applied more slowly, such as on a run-out at the bottom of a hill or in a berm whose position demands that it be run through its entirety rather than smacked into.
Fixing the suspension requires about as much work as the Honda. Put a fork kit in the front end and either lay the rear shocks at a steeper angle to justify their high compression damping and then fit them with a stiffer spring (standard spring is 82 lb./in.), or replace the shocks with proper aftermarket units.
Power is not lacking in the KX engine. Though Webco’s dyno shows it to be not much different from the other engines in this test, it is easily the most tractable. On the hard, slick tracks we encountered at Saddleback and Escape Country, both the Kawasaki and the Honda laid down some outstanding traction. . .the KX even more than the CR, which has a better tire.
SUZUKI
Gearbox operation comes very close to rivaling Honda’s as the smoothest, and is every bit as snickety-snick in operation as the RM Suzuki’s. Brakes again come close to matching the Honda’s and equalling the RM’s.
In the Kawasaki’s favor, it has an extremely low purchase price, good handling when used as a play bike, a powerband that is smoother than most without sacrificing competitive power and excellent brakes. While it may not be a great motocrosser in stock form, it is a good motocrosser with potential limited only to the amount of money an owner wishes to spend after purchase.
SUZUKI RM250
When we first began discussing this comparison test among ourselves, long before we ever acquired the bikes, we wondered by just how much the Suzuki would win. Of course, it is our job to be impartial and unbiased, but you can’t ride as many different machines as we do or as often as we do and not have at least a general idea of how far down the list a particular machine will rate. We felt that the Suzuki was at the top ofo the Japanese 250s. We were almost wrong. The Suzuki did win, but it didn’t do so by much.
Suzuki’s case-reed motor, which it refers to as “Power-Reed,” delivers good, strong torque throughout the mid-range and very competitive horsepower on top end. But the engine is not Suzuki’s forte. As the dyno chart shows, the Yamaha is more potent. Where the Suzuki does its best is in the rough. Its combination of excellent long-travel suspension and sticky tires gives it outstanding traction on a well-prepared track. In the dry, hard stuff, it doesn’t couple up as well, though. The RM steers very well, although its relatively flat triple clamps and offset front axle do not give it the impeccable line-holding capabilities of a Maico, a marque which has relied on this particular geometry in motocross for over a decade. In fact, the Suzook doesn’t even steer as well as the Honda, but it is much more stable at speed.
The improvements over the TM series motocrossers which preceded the RM are too numerous to name. In fact, the RM has nothing in common with the TM except for the brand name on the tank and brake cable housings that compress excessively, giving the binders a touch of mushiness. With stronger cable housings the RM’s brakes could have been the best. They are strong and very progressive in application, but give poor feedback when clamped on hard.
YAMAHA
For a while we were puzzled. The RM370 we tested several months ago had a very rigid swinging arm. Since the 250 shares the same frame with the 370, we expected that the swinging arm would be just as sturdy, if not more so. Yet when landing slightly sideways from cross-up jumps, the rear end would swap a little, as though the swinging arm were flexing. Finally it dawned on us what was happening. The RM370 uses an IRC rear tire that has a low profile very much like that of the Dunlops found on two of our other three test bikes. But the Bridgestone on the RM, while providing good traction, is a very tall tire. It has a lot of sidewall. What we were getting was sidewall whip when we landed sideways.
The large tire sidewall would flex to the side as the tire compressed unevenly
due to our landing position. Then as the pressure on the tire was alleviated, the displaced air inside the tire would rush back in to the compressed area and bring the tire back to its original shape. This caused the tire to whip the tail end of the machine to the opposite side. Since such whip is undamped by any shock absorbing device, it occurs in seauentially diminishing numbers until the initial load placed on the tire has been sufficiently alleviated. This is not a phenomenon particular to the Suzuki. It happens on each and every motocrosser. However, due to the large sidewall area on this particular Bridgestone tire (which is easily double that of a Dunlop 4.60), it was strong enough to bring it to our attention.
SUZUKI
RM250
$1410
YAMAHA
YZ250
$1324
SUZUKI
YAMAHA
YAMAHA YZ250
The first things we’re going to tell you about the Yamaha are the things that are wrong with it. The tires have got to go. While the Kawasaki can get away with the Dunlop tires, the Yamaha, which has more power and greater steering rake, cannot. The rear tire is passable in most situations except the hard, dry stuff. The front tire isn’t passable anywhere. It would probably wash out as the machine was being pushed off a dealer’s showroom floor.
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The 3.00-21 knobby has nothing resembling knobs anywhere near the sidewall. This makes it effectively narrower than other 3.00 cross-section tires. On the sand track it knifed in and made steering heavy; on the dry tracks it cornered like roller skates on an ice rink, like leather soles in the rain, like a pizza board on marbles. Get the picture? Good.
The other problem was with the rear brake. It is the same toggle-switch unit that has plagued Yamaha for the last five years. We put a Z-bend in the brake rod to desensitize it a bit, but it was still either on or off. So what we had to work with was a bike that got through berms okay, but went into each corner with the rear wheel locked up and cornered bermless turns like an illloaded wheelbarrow. Why then were the Yamaha’s lap times so quick? Simple. The YZ250 is fast, bloody fast.
To begin with, it is geared taller than the other three machines. It would go through turns in second just as fast as the others would in third. It has the torque to pull the taller gearing. And not only pull it, but pull it harder than the others pull theirs. On dry tracks this meant a lot of wheelspin, something that a better tire would help cure. But when track conditions were right, it coupled up and blew out of corners like the Tokyo-Osaka Express.
None of the other bikes could touch it in the drag races. All of the bikes started in second gear. Had the YZ been geared like the CR, RM or KX, it probably could have taken off in third. When at speed, the suspension worked like a charm. Front fork action was better than the Suzuki’s, but the RM’s rear end is better behaved, sidewall whip aside. The Monoshock still has a tendency to hop a little coming into corners, a trait that wasn’t aided in any way by the touchy rear brake.
Shifting the Yamaha tranny is mildly demanding. The shift lever is too short, reducing the leverage that the rider’s foot applies. Our shift lever was improperly positioned when we received the bike, so we dropped it down one spline on the shaft. When you do this, it is necessary to completely remove the left footpeg. We found that the best way to ensure positive gear engagement was to roll back the throttle and clutch all upshifts. With a different shift lever, clutchless shifting would be much easier.
NOTES
The Suzuki’s rear brake cable is difficult to adjust. In the future, we suggest that Suzuki move the adjustment from the backing plate to the forward cable stop. The RM suffered from severe detonation in the mid-range. This was cured by installing a Q6 needle jet. The new jet richened up the mid-range and added just enough to the top end so that we had to bring the main jet down from a 310 to a 300.
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The Honda’s grips, which were at one time admired as being very good, have stagnated themselves to the point that they are now the poorest of the lot. They aren’t soft enough nor large enough for average size hands. Their small diameter increases the chances of forearm cramps. The KX’s grips were almost as bad.
The Yamaha vibrates excessively at low engine speeds. We checked all of the motor mount bolts, but could find nothing loose.
All of the machines come equipped with Daido (D.Í.D.) 520 chain. Stretch was totally uniform. The Yamaha’s clutch gets hot and drags if kept pulled in for more than a minute while in gear on the starting line. The chain tensioner and skid plate are nice extras on the YZ. The Kawasaki has the only fuel tank opening large enough to peer down while filling. Everything else overflowed and got doused each time the tanks were topped off.
IN THE END
The Kawasaki and the Honda need help, mainly in the suspension department. We’d race either of them for fun at the Dunes or Escape Country, but wouldn’t even think of throwing a leg over one at Carlsbad without the modifications mentioned.
The Yamaha and Suzuki are the two best. The YZ chased the RM throughout our test, waiting for it to make a mistake so it could slip past. The Suzook didn’t bobble. The Yamaha could have won this test with a good rear brake and better tires. We’re sure that Yamaha knows that its originalequipment rubber isn’t up to snuff, but they’re the ones who chose to install it. Tire and brake changes would probably also bring the cost up into the $1400+ category that the RM is in. But price didn’t seem to bother the folks at Suzuki. They went out and they built right, from end to end. You have to pay a little more, but in the end, you get a little more.
