1973 Suzuki RN73

1973 500cc World Champion

Roger DeCoster's 1973 World Championship Suzuki on the "Grass Track" at Red Bud Michigan.

The Suzuki RN73 Back Story:

At the end of 1972 Suzuki was on top of the motocross world. The Japanese factory had taken Europe by storm owning both the 250 and 500 World Championship rider and manufacturing cups that for years had been so precious to the European manufacturers. Roger DeCoster gave Suzuki their 2nd consecutive 500cc World Championship in only their second year competing in that class. The works Suzuki’s were the result of an enormous R&D development program that began back in 1965. The frame geometry, suspension and engine performance were a combination far superior to anything that anyone else had to offer. Suzuki used very clever engineering and weight efficient design in building extremely lightweight grand prix bikes. The 1972 open class GP bike that started development in 1970 was dubbed the RN72 and was far superior to anything in the day. In 1972 DeCoster was in the best shape of his career and felt he was stronger than anybody else on the track. This combined with the RN72 gave him so much confidence, that he felt he could start last and finish first in any race at any time.

There was so much momentum at Suzuki over the last several years, it seemed like 1973 would be another repeat, after all, who could stop them? They had the best riders in the world; they had developed the best bikes in the world, bikes that no one had even conceived before. They had a very efficient program with a very focused and dedicated team. Suzuki would listen to the riders and make changes to the bikes much faster than had ever been done before. This approach alone put them way ahead of the curve.

Dark clouds however, for Suzuki were looming and nobody, not even the most astute student of the sport saw what was to come the following year. In 1973 the rules would change, the Suzuki works bikes would be banned, a World Champion would fall and the Suzuki factory that was on top of the world just a year earlier, would all but abandon its own team. It was also the year that long travel suspension would be introduced, instantly making short travel bikes obsolete. Motocross engineering was about to enter an era where advancements in design would change so rapidly that this weeks winning bike may become obsolete the following week.

In the winter of 1972, the once dominant European factories led by Maico filed complaints against Suzuki with the sanctioning body the FIM. Led by Maico factory rider Gerrit Wolsink, the complaint was that Suzuki with it’s millions of dollars were building machines that were too light and dangerous and were making it impossible for the much smaller European manufacturers to compete with. Suzuki was so secretive about their bikes and how they made them so light that this led to wild speculation by everyone as to how they were built so light.

During and after the Trans AMA series in the fall of 1972, development was going on in Japan for the 1973 Suzuki GP bikes. They had already achieved the ultimate in power to weight, the frame geometry was refined, and now for 1973, Suzuki turned their focus on suspension. Most of the attention was on designing and building larger suspension units with increased oil capacity and experimental progressive spring rates. The increased speeds that the 1972 GP bikes were capable of were causing the suspension to be stressed and the oil viscosity was breaking down early causing premature suspension fade. They were also realizing the need for rising spring rates. These problems were addressed and solved and the 1973 Suzuki GP bikes were built and ready to dominate once again.

Right before the 1973 GP season was to begin; the FIM announced that there would be a major change in the1973 FIM rulebook. There would be weight limits imposed and the Grand Prix Suzuki works bikes that were already built, were some 30 lbs. too light. The FIM caved under pressure from the other manufacturers and the brand new works Suzuki’s that were designed, built and ready to be sent to Europe were now banned.

This was a huge blow to Suzuki and left the Japanese manufacturer with the feeling that whatever hard work and engineering they put into there bikes would be penalized by rule changes from the European establishment. If this wasn’t enough, the bikes were put even further behind the curve when long travel made its debut with the Yamaha monoshocks and then the Maico long travel bikes. These bikes had over 50% more travel than the conventional suspension works Suzuki’s. With lack of factory support, Roger along with teammate Sylvain Geboers would end up taking development matters into their own hands to keep the works Suzuki’s on par with the other long travel bikes. The season wound down to one of the most dramatic finishes that went to the final moto at the final race at St. Anthonis in Holland where Roger narrowly defended his title by defeating factory Maico rider Willy Bauer.

Today Roger’s bike is in the exact unrestored original condition as it was last raced in 1973. The bike, in and of itself is a story. It is the preserved remnant of a champion from one era struggling and doing whatever it takes to become champion in a new era. It is one of two bikes that Roger used in the 1973 500cc world championships. The bike was also used in the 1973 Motocross des Nations at Wholen Switzerland before it was retired.

Roger De Coster and Terry Good pose with the world championship RN73 at Roger's home January 2000.

1973 Suzuki RN73 Photos                Order a photo CD of this bike with over 200 hi res photos in the store section

Roger De Coster’s comments:

Right before the 1973 GP season began we were notified by the FIM that the rules had changed and there was now a weight limit of 209lbs. for our open class works bike. Our 73 GP machines were already developed and built and were about to be sent to Europe when we got the notice. There was no time to build new bikes so the Suzuki engineers had to artificially add ballast to the bikes. This was initially done by pouring lead into the frame center down tube, replacing all of the titanium hardware with steel. The sand-cast magnesium engine had lead poured in the empty spaces in the center cases and was later sand-cast in aluminum, the steering stem that was originally aluminum was replaced with a steel one. By doing this it completely threw the bike out of balance. The bike didn’t get traction as it did before, the handling was compromised and the suspension didn’t work as well. We knew we were in big trouble going into the first GP race of the year at Tarare France.

The French Grand Prix was a very hard and rocky track. We were at a very big disadvantage to the Maicos that had a smooth powerband and hooked up much better than our short stroke Suzuki. We weren’t sure if it was the motor difference or because we lost our weight advantage or what. I ended up with a DNF in the first moto and of all things; it had nothing to do with our ill handling bike. It was a stuck throttle that caused the DNF. On one of the long down hills the throttle stuck and I nearly killed myself and had to stop. In between motos I heard some gossip from one of the riders that I was all washed up and just making excuses. In the second moto I proved them wrong and won the moto but the stuck throttle problem would come back and haunt us several more times during the season.

At the third round at the Finnish grand prix, the Yamaha monoshocks came out and they had 50% more rear suspension travel than anybody so now everybody was behind in suspension. We started experimenting with different rear shocks with larger bodies and conical springs but Suzuki management had changed and they were still very frustrated with the FIM and the rule change. Because of all this, I felt we weren’t getting the support necessary to keep up with all of the new developments that were taking place. Things were changing very fast and at the fifth round in Holice Czechoslovakia, which was a very rough track, Willy Bauer’s factory Maico now had long travel suspension with forward mounted shocks. I had a very big battle with Bauer that day. I pushed hard and was riding very well but ending up getting second to Bauer. At this time I was getting very frustrated as we were falling behind again.

For round five at the first ever points paying USGP we shipped the bike to the states and again I rode very hard but struggled with handling and traction problems. The Maico's were getting very good traction with the new long travel suspension and their bikes adapted better to the hard southern California terrain. This gave Willy Bauer and the Maico team a huge advantage and again I came up short. We had to do something if we were going to retain the championship.

In Bielstein Germany we had a new frame that allowed for longer shocks but this wasn’t enough. It was getting late in the season and I was behind and something else had to be done. This is when my teammate Sylvain Geboers and I took matters into our own hands. We decided to modify the frame and move the shocks forward similar to the way the Maico’s were set up. We made some sketches by hand and took two spare frames cut them up; added 20mm spacers to compensate for the longer travel and tacked them together. We then took them to our mutual friend Lucien Tilkens shop and he welded them up as he was a very good welder. For rear shocks I made some aluminum shock bodies with cooling fins myself and took them to Koni and they set me up with rear shocks using the bodies that I had made. This made a very big improvement and now we were equal with the rest of the bikes in rear suspension.

Going into the final race at St. Anthonis Holland, Bauer was leading the points but my bike was working well and I knew I could beat him in the sand. During Saturdays time trials one of the Suzuki engineers decided to take a fuel sample because the track was a long deep sand track that robbed power and used lots of gas. He determined that I would run out of gas before the 40 minutes plus two laps race ended. We checked all of the spare gas tanks we had with us and they were all exactly the same. My mechanic was literally in tears and we didn’t know what to do. We figured we would be about three laps short. Back then there was no fabrication shop around so I decided to call Tilkens who was in Belgium, about two and a half hours away. Mr. Tilkens said to bring the tank to his shop and he would make it bigger. He was the kind of guy that would stay up all night to help. I got in the car and drove the two and a half hours to his shop where he spent a good part of the night modifying the tank. He split the tank open like a sardine can and added to the top for extra capacity. The modification added about a liter and a half, which would be plenty to finish the race. Then I drove back to Holland in the middle of the night and I didn’t get much sleep but I knew I had to win the next day and I was confident that I could win in the sand. As it turned out I did win and was world champion for the 3rd time.


St Anthonis Holland: DeCoster #31, Bauer #41 and to the right Ake Jonsson #36 at the start of the final moto.

Ake Jonsson on the infamous Yamaico and De Coster drag race down a sandy straight during the final moto in the final GP at St. Anthonis. Open stingers all the way, yeah! Can you imagine how loud that moment was? Ake won the race and Roger won the Championship. Note the sand tank on Roger's bike.

De Coster’s comments continued:

When I first signed with Suzuki, I was elated just to be on the team. When I first started testing their bikes I was very surprised that they would listen to me and make changes that I recommended. After my first year at Suzuki, I thought that a five-speed gearbox would be better on the race track than the four-speed we were using. They built one for me and I was right, the five-speed worked better. It was awesome to be listened to. It was like being in seventh heaven. This had never happened when I was a factory CZ rider. At CZ the engineer was always right and the rider was always wrong and more often than not, the rider got blamed for things that broke or went wrong.

The RN 370 was an awesome bike, it made awesome power and had exceptional throttle response, it was instant and crisp at all times. The actual displacement was 372cc and the power characteristic of the motor was very abrupt especially in the lower gears. This actually had a significant impact on my riding style as it made so much power. The problem we had at the French grand-prix with the throttle sticking turned out to be the vacuum of the cylinder that was keeping the slide from coming down. It took nearly all season to figure this out. Suzuki made several modifications to fix this from heavier throttle slide springs to grooved slides to minimize the contact with the carb body.

Winning the world championship in 1973 was very difficult and I was very relieved when it was over. I had tied Paul Friedrichs record of winning the 500cc world championship three times in a row.

Nobody thought we would win the world championship our first year out and we did it. Nobody thought we would win three in a row either. It had only been done one time before and that was Paul Friedrichs on the CZ. To win with this bike in 1973 and tie Friedrichs’ record was a very big accomplishment especially considering all the changes to the sport that happened then. Suzuki and I worked very hard to win in 71 and 72. At the end of 1972 I was prepared mentally and physically and looking forward to defending my title in 1973. We were caught by surprise by the late change in the FIM rules as our bikes were already built. The bike did not respond well initially to adding weight ballast to meet the new rule and we started out the season at a huge disadvantage.

I knew I had the experience and the ability to win that year but it was very frustrating because of the sudden rule change and also because Suzuki didn’t react fast enough to the long stroke suspension that Yamaha and Maico had. Suzuki was pretty bummed out by the FIM rule change and felt they were unfairly treated. The frustration that Suzuki had over this and an internal management change did lead to a lapse in support.

I felt Suzuki was unfairly criticized for the bikes we had that led up to the minimum weight rule change. I had heard the complaints from the other teams that led up to the decision to impose the minimum weight limit, but the accusations they were making were not true. Our bikes were safe and we did not use all of this space-age stuff that they were accusing us of. Years before, BSA used way more titanium in an attempt to accomplish the same thing and they were praised for it. The magazines wrote about how cool and high tech it was but when the Japanese came in and built small, lightweight and nimble bikes using clever engineering, they were penalized for it.                                                                                                                                                  

At the end of the1973 season, I went to the Suzuki race team management and told them, “You guys have to do something, we just won all these championships in the 250 and open class and now were going to give it up? We have to keep winning. They realized they had to make changes and for 1974 we developed a long stroke motor and a chassis with long stroke suspension.

The Japanese had a much better attitude and were much more dedicated than the European manufacturers and that is why they succeeded. When we were in a different country at a GP and something went wrong, they went to the nearest post office immediately and sent telexes to Japan to correct the problem. Instead of blaming the rider, they listened to the rider.

In the beginning of the 73 season when we were at a clear disadvantage, I always had two things in my head. I knew I could be beaten because there was this worry side in me. But, there was another force in me that told me “I can win today, I don’t care how good this guy is, I can beat him.” If I didn’t win that day, I would think, “Well, I screwed up here or my bike was not so good but next week is going to be my turn.” I never gave up and always believed I would win.

 De Coster battling for the holeshot with Maico's Willy Bauer during the first ever USGP at Carlsbad. This is the very bike in this collection.

 De Coster nearly drags the bars as he slams into a berm during one of the many epic battles he had with Willy Bauer in 1973. The championship went down to the final moto of the final GP

Trying to keep Bauer in sight at Holice Czechoslovokia. This was first race Bauer's Maico had the forward mounted shocks, putting DeCoster's Suzuki at a disadvantage.

Detail Photos

Historical Photos