Trials Bikes For Dummies

By Ron Milam

This month I would like to start a discussion on suspension theory and setup. This is an area that can make or break the way your bike performs, regardless of its age. If you start adjusting on your new bike you can easily ruin the turning ability if you do not keep a few simple principles in mind. On the other hand, if you get lucky and find some good settings as I recently did, your old bike can suddenly become “new” again.

I think a little history may be interesting as an introduction. Those of use that started riding many years ago may know some of this already, but the younger guys were not born when single shock suspensions came about. And any of you that think Yamaha invented the single shock concept, think again. When I was a teenager, I had a 1960’s NSU 150 that had a single shock mounted inside its stamped steel frame. There were probably earlier bikes than this with single shocks, but the current type of suspension that we are familiar with grew out of an idea from a Belgian gentleman named Mr. Tilkins. This was during the early 1970’s. Suzuki ruled the motocross world with the “Dream Team” of Joel Robert, Roger DeCoster, and Sylvain Geboers. Joel and Sylvain were number 1 and 2 in the world 250 class. Roger was number 1 in the 500 class, closely followed by the Swede, Ake Johnnson who rode for Maico. I may be misspelling a few names here. I am going off of memory from nearly 30 years ago. Anyway, the entire Suzuki team was Belgian, and they liked to hang around at Mr. Tilkins place. He was an skilled craftsman who loved motorcycles. He had an idea to mount the rear shock horizontally and connect it to the steering head. His theory was (so the story goes as later told by DeCoster) that the bumps absorbed by the shock would be redirected to the steering head and would push the bike forward. He told the riders about it and tried to sell the idea to the Suzuki team. The Suzuki engineers realized that his theory was wrong and the horizontal shock would not make the motorcycle go any faster. So, he approached Yamaha with the idea. Their engineers also were smart enough to know it wouldn’t work. But, they saw another value in the concept and bought the idea. That idea soon stunned the motocross world, when in 1972 I think it was, Yamaha fielded a 500cc class machine utilizing the concept. The Monoshock was born. In the first G.P. of that year, a Swedish rider who I believe was either Christer Hamergren or Hakan Anderson upset both the Suzuki and Maico teams aboard the prototype Yamaha to win first place. After a few races it was clear that the concept was far superior to the existing twin shock rear suspensions that boasted travels of about 4 inches. Fork travel at that time was approximately 6 inches. The Maico team was the first to figure out that the advantage was in the longer travel afforded by the monoshock arrangement. For you younger guys, the original monoshock had no linkage. That was not to come for another 7 years. With no time to design a new bike, the immediate problem was solved by a Maico mechanic who simply moved the shock mounts forward on the swingarm and frame and bolted up the existing Koni shocks (the hot setup back then ). The result was about 6 inches of rear travel. The bike was immediately competitive with the Yamaha. Rapid development in shock design began. Standard shocks could not stand the higher temperatures and pressures of the longer travels. Fade and blown seals were common. The next few years saw progress and fads come and go. Air shocks and air forks without any springs were tried with some success. Then combination air/spring designs came and went. Many vintage bikes still have vents in the fork caps from the era when riders wanted only the influence of the spring, without any effect from the air trapped in the fork. The next big improvement came about 1979 when Kawasaki introduced the Uni-Trak. This was the first modern rear suspension to utilize a linkage to vary the mechanical advantage between the shock and swingarm. Like the Yamaha Monoshock, this was a major advance which resulted in success on the race track. Within 2 years, both Honda and Suzuki also had linkage type systems. Of the 4 Japanese designs, the Honda Prolink system was the one that endured, becoming the forerunner of the suspensions used on most off road bikes today. It took until the mid 1980’s for the concept to appear in trials bikes. However, while front and rear travels of most motocrossers have grown to about 13 inches, modern trials bikes have travels of about 6 to 7 inches. I know a lot of this story was not about trials, but both trials bikes and go fast bikes continue to evolve from the same pool of technology. The have disk brakes and watercooling. We get that and return the favor by giving them aluminum frames and hydraulic clutches. Their past is our past. Their future is also our future. Next month, I will get into some suspension theory.

Ron