Chapter III: Evolution of the Monocross Suspension

A Day to Remember

August 5th, 1973 was a historic day for Yamaha Motor Co., Ltd. as well as the motorcycle industry. It was the Finnish round of the 250cc Motocross World Championship and the day that Hakan Andersson rode to wins in both motos on a Yamaha YZM250 factory machine equipped with a revolutionary new suspension. These victories brought Andersson his and Yamaha’s first motocross world title.

It was a moment that decisively proved the competitive potential and future possibilities of the single-shock “Monocross Suspension,” a device that would soon become the new standard worldwide for motorcycle suspensions.
World Champion Hakan Andersson surrounded by mechanics and development staff members. His results for the year are on the right.

A Wise Decision

The story of this great achievement had actually begun the previous year. Having sparked a worldwide off-road riding movement with the release of the DT-1, Yamaha decided that in order to achieve a new level of technological capability, taking on the challenge of winning the world’s premier off-road competition was a necessity, and began competing in the Motocross World Championship. It would be no easy task to win the title, however. Standing in the way was a formidable group of rivals that included the European manufacturers of Maico, Husqvarna, CZ as well as Suzuki, which had already established a formidable presence in the sport.

As a latecomer, Yamaha was in a position where it would certainly not win using the same means as the competition. On top of that, accomplished riders would not choose to ride with Yamaha unless the bike they would ride had some kind of revolutionary new technology.

Yamaha’s development team had already succeeded in winning world titles in road racing and had accumulated a wealth of engine development knowhow. Realizing how the chassis—and suspension performance in particular—is essential in motocross, Yamaha set to work ahead of the other manufacturers to learn about new suspension-related technology. Instead of depending solely on established suspension manufacturers, Yamaha resolutely began suspension development efforts of its own. That same year, new “Thermal Flow” rear shock absorbers were equipped on its factory machines. To solve the problem of inconsistent damping force resulting from the rise in damping oil temperature when in use, the new Thermal Flow rear suspension’s shock absorbers had three times the volume of oil of standard shocks and the oil tanks were fitted with fins for added cooling capacity. This improved performance and race results, including a win in the 250cc class at Round 10 in Sweden and the 500cc class at Round 11 in Luxembourg. But, the Yamaha teams were still a long way from winning a championship.


An MX125 production motocrosser equipped with a Thermal Flow rear suspension

It was one day during the 1972 season that one of Yamaha’s riders, Jaak van Velthoven, told the leader of GP team, Toshinori Suzuki, about an interesting new machine and suggested that they go see it. Suzuki took that advice and afterwards went to visit the home of Belgian engineering professor Lucien Tielgens, who had invented the “interesting device.” What Suzuki saw in the professor’s workshop was a single-shock suspension unit. After that visit, he contacted Yamaha’s European base, Yamaha Motor Europe N.V., and the headquarters in Iwata, saying, “This might contribute to improved performance for a motocrosser and is worth investigating.”

The response at Yamaha headquarters was quick and decisive. Measures were taken to have the single-shock suspension modified to fit a 250cc factory machine. In order to test its performance, a team including Noriyuki Hata, Kazuhiko Nomura and others secretly gathered at a small course in a Belgian village named As in September that year.

After the Yamaha-contracted riders took it out for test runs, they said that it wasn’t slow but it didn’t run well either because it didn’t give them a feeling for the bike’s power. Still, the lap times were not particularly slower than usual. It was at that point that Nomura noticed that the muffler had been dented. That meant that the machine had been running those times despite it not delivering the usual power output! That, in turn, meant that the bike was able to run more smoothly with the new suspension! Recognizing a difference in the way the machine landed from jumps, Hata, the director of Yamaha’s R&D department, made an immediate decision. The price to acquire the patent for the new suspension was not small by any means and represented a huge investment for Yamaha Motor at the time, but Hata convinced top management that this suspension was a diamond in the rough; it would shine beautifully with some refinement. 

Kazuhiko Nomura recalls what it was like: “Being a latecomer to motocross, Yamaha was very keen on making progress with suspension development and we were doing a lot of research in that area. Before we started development of the Monocross suspension, we already knew that if the cushioning performance was improved, it would make a big difference in motocross. That’s the very reason that we recognized the great potential of the single-shock suspension as soon as we saw it, and that helped in making the decision to develop this completely new kind of suspension device.”

Diligent Development

That first prototype machine with the single rear shock unit was immediately sent to Japan. After arriving in Iwata in October, it was taken to Yamaha’s test course at the Tenryu River near the headquarters to be tested by contracted rider Hideaki Suzuki. His first impression was that the machine lacked power but it was easy to ride. Still, he was worried about the lap times the bike would run. Like the test riders in Europe, Suzuki was used to riding machines with two rear shocks and he didn’t feel like he was riding fast. But the times told a different story. On a roughly 1 km course, he was posting lap times about three seconds faster than usual! The riders and engineers were amazed at the potential this new suspension had shown. The development team immediately set to work to improve the technology and get it into practical use as soon as possible.

“The first thing we concentrated on was refining the mechanism that produced the damping force,” recalls Nomura. “We decided that we should accumulate knowhow ourselves about the key parts of the unit, and we used things like the process for changing carburetor jets to develop an exclusive mechanism for producing damping force.” Another key point for a shock absorber is how it is mounted to the chassis. For this shock absorber that would be positioned basically along the fuel tank rail, the positioning of the air cleaner became a problem. “We made countless design sketches. In the end, there was simply no more time for drawing plans, so we began making the shapes with Styrofoam and clay to work out the possible spacing. It was during this process of trial and error that we got the idea of making a triangular swingarm,” he adds.

Once it was decided that the new mechanism would make its debut in the opening round of the All Japan Motocross Championship the next year, the development team began working late into the night, day after day. As for the placement of the air cleaner, it was positioned beside the engine for the 250cc model, while the 125cc model had units on both sides.

After this and numerous other difficult design and engineering problems were overcome, such as how to seal the shock’s nitrogen gas, the team finally completed a handmade factory machine with nearly twice the stroke of a conventional rear suspension. The three 250cc machines and three 125cc machines were ready just in time, and were loaded into a truck at Iwata to be transported to Yatabe, Ibaraki Prefecture for the March 1973 opening round of the All Japan Motocross series.

Proving Its Worth

Hideaki Suzuki scored a debut win in the 1973 All Japan Motocross Championship season opener on the YZM250.

March 18th was the day of the 1973 All Japan Motocross Championship season opener. When the new Yamaha factory machine went out for the practice sessions, the race venue was soon alive with exclamations of the crowd’s confusion about what they were seeing: “Hey! That bike’s got no rear suspension!” Because the new suspension was positioned inside the frame under the fuel tank, it was invisible from the outside. What’s more, these new Yamaha bikes were jumping higher than any of the competition.

When the races were over, Torao Suzuki had won the 125cc class race and his older brother Hideaki Suzuki had done the same in the 250cc class. It was an overwhelming victory for Yamaha; these machines with their new Monocross suspensions dominated the podium in both classes. The Japanese media quickly dubbed it the “Flying Suspension,” and the news of its performance quickly spread around the world.

After its stunning debut in the All Japan Motocross Championship, the now-publicly-known “Monocross suspension” was put to the test in the 250cc and 500cc classes of the Motocross World Championship, the pinnacle of motocross racing. It would first show its advantages in the 250cc class.

Before the opening round of the 1973 series in February, Hakan Andersson saw the new YZM250 for the first time at the course in As. Looking back on the experience, Andersson mentioned how he was surprised at how he’d managed to set lap times similar to the twin-shock bike because the characteristics of this new suspension as it had been developed and set-up in Japan didn’t immediately mesh with him. There was a difference between Japan and Europe in the way rebound and compression damping was used.

After the necessary adjustments to the settings had been made to accommodate for this difference, a machine mounting the Monocross suspension finally made its GP debut at the third round of the World Championship in Belgium.

Andersson finished 3rd in the first moto and won the second one. The racing success continued in the next round in Yugoslavia where he won both motos on the new machine. At the next round in France, Andersson got off to a bad start in the first moto that left him at the back of the pack, but he managed to roar back to finish 2nd and nearly win the race. He then took a runaway victory in the second moto.

Hakan Andersson riding during his 250cc title-winning year of 1973

Having seen his astonishing performance, the dumbfounded race officials decided to give Andersson what would be the first and only drug test of his career. That is just how shocking Andersson and the Monocross-equipped YZM250 had been.

At last, the day of the Finnish GP, the eighth round of the series, had arrived. Andersson won both motos, finally becoming a Motocross World Champion in what was a truly historic moment. This tremendous feat also came just one year after the Yamaha development team had laid their eyes on a single-shock suspension for the first time at the course in As, Belgium.

Furthermore, it wasn’t only in the 250cc class that these accomplishments were taking place. After his spectacular win in the opening round of the All Japan Motocross Championship, Torao Suzuki also entered the FIM 125cc Motocross Prize series in Europe and went on to become the Group A champion on a YZM125 machine with the Monocross suspension. On September 23rd in Yugoslavia, he competed for the overall title as one of the top 30 riders (15 from Group A and B) and finished 3rd in the first moto and 1st in the second moto to place 2nd overall in the series. These showings left a very strong impression of the strength of Yamaha and Japanese riders among the motocross fans of Europe.

In 1973, Hideaki Suzuki (right) won the 250cc All Japan title while his brother Torao Suzuki (left) won the 125cc title.

Spread and Development

The overwhelming success of the Monocross suspension and Yamaha’s motocross machines spread to North America as well. Amidst the rapid growth in popularity of off-road riding following the release of the DT-1, Yamaha Motor’s sales company in the U.S., Yamaha Motor Corporation, U.S.A. signed a contract to bring Dutch national motocross champion Pierre Karsmakers to its racing team in 1973. As Karsmakers gradually got used to the American style of competition, he managed to clinch the AMA 500cc Motocross title that same year. Then in 1974, he entered the new AMA Supercross series and became its first champion riding a YZ motocrosser with a Monocross suspension.
“I think we worked probably six to nine months on [the Monocross suspension that arrived from Japan] to get it tested to where it was very, very good,” he recalls. “But the biggest problem we had actually with the monoshock was that the rear became so good; it got better, and better and better all the time...we couldn’t keep up with the front forks.
“When I had a proposition for something or wanted to change something, [Yamaha] always listened and had meetings about the problem and we always tried to make the product better...I always felt that I was part of the family with Yamaha.”

Thanks in large part to Karsmakers’s efforts, Yamaha became very successful in America. One of the great stars leading the Yamaha charge was Bob Hannah. In 1976, he became the AMA 125cc National Motocross Champion and then won the Supercross title three years in a row (1977–1979). Another star was Broc Glover, who became the youngest AMA 125cc National Motocross Champion ever and contributed to many articles in the media about Yamaha’s “takeover” of America. As the passion for off-road riding continued to grow in the U.S., the Monocross suspension became a shining icon of Yamaha’s presence. And, this was only the beginning of what would become an era in which Yamaha reigned as the leading brand in motocross.

Pierre Karsmakers was invited to ride in Japan after winning the 1973 AMA 500cc Motocross Championship.
Bob Hannah out on a Supercross track
Pierre Karsmakers was invited to ride in Japan after winning the 1973 AMA 500cc Motocross Championship.
Bob Hannah on a Supercross track

With its performance advantages proven on the factory machine, the Monocross suspension was quickly adopted on the YZ250 production motocrosser the very next year, 1974, to begin making it available to anxiously waiting motocross fans around the world. After that, use of this suspension would spread to many models—off-road and road-going alike—and its technology contributed to a major revolution in motorcycle chassis design.

Single-shock rear suspensions are no longer a novelty by any means; they are now the de facto standard for motorcycles. However, the first Monocross suspension that pioneered these devices was the product of a passionate team of Yamaha engineers and riders that worked tirelessly to fine-tune it into a revolutionary technology that uniformly changed motorcycle design. The passion—verging on mania—of these engineers and riders would enable Yamaha to pioneer a new genre of off-road machines and new horizons of technological development.

Reference Videos

Yamaha Monocross Suspension

A video created in 1973 describing the Yamaha Monocross suspension.

Yamaha's First Motocross World Champion and the Monocross Suspension

1973 250cc Motocross World Champion Hakan Andersson reflects on his title-winning year with the Yamaha Monocross suspension.

Pioneering the Sport of Motocross in the United States

Pierre Karsmakers, winner of the first AMA Supercross Championship in 1974, talks about the early days of motocross in the U.S.

Memories with Bob Hannah

Keith McCarty, Racing Division Manager at Yamaha Motor Corporation, U.S.A., reflects on his years with Bob “Hurricane” Hannah from 1977 to 1979.