For this edition of Classic Steel we are going to take a look back at Suzuki’s first water-cooled, single-shock motocrosser, the 1981 Suzuki RM125-X.
In 1981, Suzuki injected a huge dose of works trickery into their 125 program with the introduction of the all-new RM125-X. Photo Credit: Suzuki
Today, Suzuki’s motocross effort is a mere shadow of its once-glorious past. As of 2019, they have pulled out of racing in Europe and Japan and only maintain a tenuous hold on the US scene through the efforts of their partner Joe Gibbs Racing. Once the holder of an incredible ten 125 World Motocross championships in a row (the first ten run in fact, from 1975-1984), the once-proud marque looks to be on the ropes.
Sayonara dual-shocker: After finishing second to Yamaha’s YZ125 in 1980, Suzuki ditched everything but the throttle, grips and shifter for 1981. Photo Credit: Suzuki
In the 1970s, however, this situation would have been unfathomable. After stumbling slightly out of the box in the mid-sixties, Suzuki had come roaring back to dominate motocross racing on the world stage in the seventies. With riders like Olle Petterson, Joël Robert, Roger DeCoster, and Gaston Rahier on board, the ultra-trick Suzukis won title after title during the decade.
Floater: One of the major changes on the RM125 for 1981 was the addition of Suzuki’s all-new single shock rear suspension system. Coined the “Full Floater” for its unique “floating” shock arrangement, this system used a series of rocker arms, pull rods, and linkages to compress the shock from both the top and the bottom simultaneously. Photo Credit: Suzuki
After dominating the GP scene, that equipment advantage finally started making its way to the common man in 1975. The introduction of the RM line, with its long-travel suspension, powerful motors and lightweight chassis, finally made good on all the promises that the earlier TM series had failed to deliver on. Small, scrappy and fearless, Suzuki showed with the RMs that they were more than capable of taking on both the established Old World powers of Europe and their own larger domestic rivals.
In 1980, Mark Barnett (number 10 above, leading Kawasaki’s Jeff Ward) used a prototype version of the Full Floater to capture the first of his three 125 National Motocross titles. Photo Credit: Motocross Action
By 1980, Suzuki was concluding a five-year run at, or near the top of, the 125 standings. The RM was not always the fastest bike in the class, but its combination of excellent suspension, solid handling and usable power were hard to beat. It was a bike capable of winning at any level and a favorite of magazine editors and pro racers alike.
Buzz bombs: In 1981, the 125 class was one of the most hotly contested divisions in motocross. All-new bikes from Honda, Yamaha, KTM and Suzuki brought liquid cooling to the class for the first time, with Honda and Suzuki dialing up all-new single-shocked suspensions as well. Photo Credit: Dirt Bike
As motocross moved into the new decade, a major injection of technology began to make its way into the hands of consumers. The long-travel dual shocks of the seventies began to give way to the single shocks and rising-rate linkage systems of the eighties. Likewise, the simplicity of air-cooling started to lose out to the works cachet and added performance of water cooling.
In 1981, this was the state of the art in two-stroke design. Light, compact and powerful, the RM’s 123cc motor was capable of winning at any level from novice to pro. Photo Credit: Suzuki
For Suzuki, this transition took place in 1981, with the introduction of the all-new RM125-X. Redesigned from the ground up, the new RM shared only a handful of parts with the outgoing design. The frame, motor, bodywork and suspension were all radically changed from the dual-shock ’80 model. Literally none of the bike’s major components were a carryover, with only the throttle, grips, and shifter making the cut from 1980.
A sturdy all-new front hub featured a conical design to save weight, with ribs to aid cooling and straight-pull spokes for strength. Photo Credit: Motocross Action
Of all the changes Suzuki made for ‘81, the most high-profile was probably the introduction of their radically redesigned rear suspension system. Coined the “Full Floater,” for its unique linkage arrangement, this new design mounted a single large shock in a “floating” position between a set of rocker arms at the top and the bottom of the damper. By freeing up the shock at both ends, Suzuki believed they could provide more precise damping control and better tracking in the rough.
From 1981 to 1985, this was the best rear suspension in motocross. Even today, some hail it as the most successful design ever used. Photo Credit: Cycle World
After the new shock, the second most significant change for 1981 was certainly the switch to liquid cooling for the motor. Because simplicity and reliability often took precedence over performance in the early days of motocross, air cooling had always been the preferred method of keeping the temperatures under control in the two-wheeled off-road world. Thundering four-strokes and ringing two-strokes all relied on wind and fins to keep them from a thermal meltdown.
In order to accommodate the large shock and linkage of the Full Floater, Suzuki had to redesign the airbox and frame of the RM125. The new frame was stronger for ‘81, with beefed-up welds, additional gusseting and a new double-cradle engine compartment. Because the shock and its linkage occupied the place where a traditional airbox would sit, Suzuki had to engineer one that actually wrapped around the shock. Photo Credit: Cycle World
While simple and reliable, the tried and true air-cooled method was not without its drawbacks. Under perfect conditions, an air-cooled motor was capable of providing all the power most mortals could want, but after about 20 minutes of sustained use, heat buildup in the motor began to affect the density of the intake charge as it entered the motor. Once the air and fuel density began to drop (hot air is less dense than cool air), power output began to decrease (less molecules per cubic inch means less energy potential). Under heavy use, this could add up to as much as a 20% decrease in power at the end of a 30-minute moto. On an Open bike, a 20% loss in power was not a big deal (heck, you were probably glad it was slowing down after 30 minutes on a YZ465), but on a 125, that might be the difference between clearing Wrangler Mountain or heading straight to endo-nesia.
The pro’s choice: Handling on the RM was geared toward aggressive pilots. When under power, it turned and handled exceptionally well, but if you backed off, the chassis became less accommodating. Photo Credit: Cycle World
As the market began to shift away from big-bores and toward 125s in the late seventies, the manufacturers realized that the added cost and complexity of water-cooling might make sense on a small-displacement machine. Small motors need to be run hard to make power and as a result, were more susceptible to heat-related power loss than larger machines. By adding water cooling, the engineers could run higher compression without fear of detonation, and due to the water-cooled motor’s more-uniform heat expansion characteristics, the components could be designed with tighter tolerances. In theory, these changes would allow the motor to both make more power and maintain that power longer.
In order to keep shock temps under control, Suzuki molded a notch on the left side of the tank and bolted up a remote reservoir to make sure it could get lots of nice cooling air. Photo Credit: Cycle World
In addition to increased output, the switch to water cooling had several other benefits as well. By keeping the temperatures inside the motor more stable, jetting became far easier than in the past. The lower temperatures also improved reliability (as long as you did not bust your radiator) by lessening the likelihood of a heat-related seizure and decreasing wear and tear on the piston and rings. Even when factoring in the added weight and complexity of the radiator, water pump, and its plumbing, it was hard not to see the advantages it would bring.
Bikes like the 1981 RM125 made previously unthinkable leaps like Saddleback’s notorious “Magoo Double” actually attainable. Seeing a guy like Barnett huck this leap on a 125 was mind-bending stuff in 1981
In order to accommodate the switch to water cooling, Suzuki’s engineers had to design a completely new motor for the 1981 RM125. Everything from the piston rings to the crank seals had to be reengineered to work with the new configuration.
A new cylinder was spec’d that did away with the cooling fins completely (some early water-pumpers from Europe retained the fins on the cylinder as a precaution in case of failure) and looked literally half the size of the ’80 jug. A new head was designed that sported a similarly sparse look, with only six studs and a single water spigot protruding from its top. Internally, the cylinder kept the basic layout of the ’80 model, with a steel liner and semi-case-reed intake Suzuki called “Power-Reed.” With the introduction of Yamaha’s YPVS “Power Valve” still a year away, the new motor did without any variable exhaust ports or exhaust gizmos to broaden power.
Even without the benefit of any sort of “Power Valve” (that technology was still a year away from making it to production in ‘81), the RM’s motor produced a broad and potent power curve. Photo Credit: Cycle World
Matched to the top end was a new set of cases that incorporated a water pump into the right side. The pump was driven directly off the primary drive and featured a six-blade impeller that was capable of circulating the RM’s one quart of coolant 30-60 times per minute. Housing most of that coolant was a large single aluminum radiator that Suzuki chose to mount below the tank on the front frame down-tube. In 1981, proper radiator location was still a major question and every manufacturer had their own ideas about what would work best. To Suzuki’s credit, their location is the one that has best withstood the test of time.
A beefy alloy swingarm and lightweight conical hub highlighted the rear of the RM125-X. Photo Credit: Cycle World
On the intake side, a 32mm round-slide Mikuni carburetor handled the mixing duties and drew air from an all-new airbox. One of the engineering hurdles on the new RM actually turned out to be that airbox: because the Full Floater and its associated linkages took up the space where the airbox would normally be, the engineers had to figure out a way get sufficient air into the motor without the benefit of a single large element. The solution they came up with was a new dual-filter design that wrapped around the shock and placed one small flat filter on each side of the machine. While effective, this new design made filter servicing double the work and a real pain in the kidney belt.
The 123cc “Power Reed” mill on the RM pumped out good low end for a small bore of its day, but most of its power was farther up in the power curve. Keep it singing, and the RM was capable of running with anything in the class.
In addition to the new motor and shock, an all-new frame had to be designed that could accommodate the new suspension and increased power of the motor. Fashioned from tough chromoly steel, the new frame sported a Honda-like semi-dual-cradle design that split from a single downtube into a dual cradle just above the exhaust port; this afforded better rigidity and less torsional flex than the old single-cradle design. Both the steering head and main frame backbone were heavily gusseted, with several cross-members running under the engine to further reduce frame flexing under heavy loads.
Protect the jewels: In the early eighties, companies like Ceet Racing made big money by producing custom up-the-tank seats that replaced the stock factory nut-busters.
In order to complement all this new hardware, Suzuki’s designers went back to the drawing board and sketched out some sleek new bodywork for the RM-X. A new tank was designed that scooped out room for the radiator and shock reservoir, without decreasing capacity (1.7 gallons). New side panels cleaned up the looks and made room for the redesigned airbox, while a set of ram-scoops protected the radiator and helped direct air to it for additional cooling. A new seat was bolted on, but the padding still ended at the base of the tank, so a CEET Racing “Safety Ceet” was probably a good idea if you valued the family jewels.
Servicing the stock dual-element airbox on the RM was an arduous task that required a frustrating amount of tools and time to accomplish. Photo Credit: Cycle World
When starting the new RM125-X, the first thing a rider noticed in 1981 was how different it sounded. After decades of ringing two-stroke fins, the muffled sound of the water-cooled motor gave the bike a totally new character. The warm-up procedure was also totally new, as Suzuki recommended a full five minutes to bring the bike up to temperature before putting it under a load. This was the complete opposite of an air-cooled bike and many an early RM-X pilot found their new steed cold-seized before figuring this out.
Light in flight and nimble on the ground, the RM was a willing motocross partner in 1981. Photo Credit: Dirt Bike
Once warmed up, the new RM was an absolute joy on the track. The new motor produced a broad and easy-to-use powerband that was both fun and fast. Low-end power was good for a 125 (which in 1981, meant it actually had a little bit of it) and it really took off in the midrange. Top-end power was strong and the bike liked to rev, but its best performance was a bit lower in the curve. Overall, it was not as fast on top as the new YZ and CR water-pumpers, but broader overall and easier to ride. For most riders below the pro class, it was a nearly perfect 125 powerband.
An excellent set of 38mm KYB forks graced the front of the RM125-X. Both the spring rates and damping were well set up for aggressive riding and most pilots rated them first or second in the overall class standings. Photo Credit: Suzuki
While the motor was great, the real star of the ’81 RM125 package was the Full Floater suspension. Pumping out 12 inches of travel and offering 4 adjustments for rebound, the Floater shock was the class of the ’81 field. Under power, it was supple and smooth, without a hint of the kicking and swapping common to the Yamaha’s Mono-X. It took everything from small chatter to big whoops in stride and offered the best rear suspension performance magazine testers had experienced up to that time.
The 1981 Full Floater suspension on the RM125 was set up for charging rather than trailing. Under power, it worked flawlessly and could tame nearly any obstacle. It was only when you backed off the pace that it tended to kick and get busy. Photo Credit: Suzuki
Overall, its only flaw was that it required speed and commitment to work well. The shock was set up for racing, and if you tried to putt around, it felt stiff and busy. The Floater was set up for attack mode, and as long as you kept the throttle pinned and your race face on, it was a more than willing partner. If you backed it down, though, it was going to pound you in the coccyx.
Under the tutelage of an experienced pilot, the 1981 RM was a lethally effective weapon. Photo Credit: Dirt Bike
Up front, the new RM-X used a set of 38mm air-assisted (not air forks, they still used coil springs) Kayaba forks that produced 11.2” of travel. As was typical for the time, there were no external adjustments available. If you wanted to dial in their performance, you did that by varying the fork oil height and viscosity and by adjusting the air pressure in the forks. Of course, in 1981, there were no cartridge internals or any fancy valving systems available, just damper-rods, a spring and some oil, just as the Moto Gods intended.
Mark Barnett took a works version of the new RM125 to his second National Motocross title in 1981. Photo Credit: Motocross Action
On the track, these simple and modestly-sized forks did a great job (for their time) absorbing what was thrown at them. Like the shock, they were set up more for hammering than cruising and they could feel stiff if not ridden aggressively. At speed, however, they worked very well and made charging the track a joy. Overall, they were not quite as plush as the excellent KYBs found on the YZ125, but easily better than anything else in the class.
While the performance of the Full Floater was exceptional, its costly-to-produce design, high center of gravity and large overall size would eventually spell its doom. In 1986, Suzuki would shelve the original Floater, in favor of a more compact eccentric cam design that took up less space, but worked half as well. Photo Credit: Cycle World
In the handling department, the RM was once again the class of the field. On the track and on the scale, the bike was very light and it could be whipped, flicked and flown with ease. With its suspension settings, it worked far better when ridden aggressively, but even a spode could appreciate its feathery feel. Turning was excellent and the bike offered none of the top-heavy feel of the YZ. It was also admirably stable, as long as you kept the power on. Back it off, however, and the shock became busy and that stability went bye-bye.
Asthmatic: In addition to being a real pain to service, the RM’s stock airbox was not particularly good at getting air into the motor. As a result, nearly everyone either drilled holes in the airbox covers, or ponied up the cash for a trick aftermarket unit like this one from DG Racing. Photo Credit: Dirt Bike
In the details department, the RM was a mix of great ideas and a few missteps. Unlike the YZ and CR, which hung the water pumps out in the breeze to be damaged in a crash, the Suzuki’s was tucked in behind the pipe where it was less likely to be damaged. The radiator on the RM was also placed much lower on the frame, helping to give the bike its light and airy feel. The quality of the wheels, chain guide and bodywork were all very good and riders universally liked the RM’s slim ergonomics.
While water cooling was a major technological breakthrough in motocross performance, it was not without its early stumbles. In 1981, the manufacturers had not yet figured out the best material combinations to ensure even heating and cooling, so hot and cold seizures were common. Undersized water jackets around the exhaust manifold were also a major problem for RM125 pilots and it was necessary to have them enlarged if you did not want your new scoot to expire prematurely. Photo Credit: Dirt Bike
On the demerits side were the RM’s absurdly hard to service airbox (set aside a good 40 minutes to get into this Fort Knox), quickly wearing brakes (strong, but not long for this world), fragile clutch (abuse it at your own peril) and non-folding shifter (a $5 part that could cause a $100 repair). Piston and ring life were also suspect and smart tuners quickly found that the water passages around the exhaust ports were manufactured too small. A quick trip to a savvy shop was all that was required to keep the RM from developing a potentially fatal hot spot.
In 1981, Suzuki dropped the mic on the 125 class with one of the most advanced and omnipotent bikes of its generation. The ’81 RM125-X had the suspension, motor and handling to dominate any class, at any level. In an era where bikes were nearly obsolete the moment they rolled off the showroom floor, the ’81 RM125-X continued to be competitive long after the expiration date of the competition.
Today, the 1981 RM125-X stands as one of the most successful and fondly remembered machines of its era. In many ways, it still remains the high water mark for Suzuki performance. While they have had many great machines before and since, few have come close to the overall excellence of the 1981 RM125. It was light, fast, incredibly well suspended and super trick. It was good enough to win locally and great enough to win globally. The ’81 RM125 was the rare occasion where technology, artistry and execution converged to produce a machine for the ages.
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