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In the world of dirt bikes from Japan, all of them used some form of rear suspension with two shocks and a swing arm. Some worked better than others, but in the early years, they were all short travel, that is, from the unloaded position to fully bottomed out, most had around four inches of wheel travel. The quality of the shock, the spring rate, dampening, rebound, chassis design, and geometry all play a role in how well or otherwise the system will work.
From the beginning, suspension was a big issue with off road motorcycles. In many cases, the shocks used on dirt bikes, were the same ones used on street bikes, which led to horrific handling . The other issue was that regardless of how good a shock was, only so much could be done with a short travel system. Three of the Japanese manufacturers continued to produce motorcycles using the twin shock system until the early 1980's, but they were a far cry from the earlier models. By the mid 1970's the dirtbike industry was caught up in a suspension travel race. In some cases a chassis was designed to handle the longer shocks, as the shocks were either layed down or their attachment points on the swingarm were moved ahead. In other cases, longer shocks were installed on a chassis that was desinged for short travel syspension, which caused all kinds of issues. At this time, there were companies popping up everywhere, offering shocks and other goodies to improve the ride. Some worked, others not so well. Behind the scene there was a completely different rear suspension system and matching chassis being tested, and this would end up changing the motorcycle world for ever.
In the late 1960's and engineer named Lucien Tilkens was working on a rear suspension system for motocross bikes, which used a large single shock and a triangulated swingarm along with a totally different chassis. The first one known to be built was for the CZ factory in Czechoslovakia, who were a major force in world motocross. The benefits of a single shock included more wheel travel, better dampening and rebound, and a great leap in handling. The drawbacks included extra weight, and because of the almost horizontal position of the shock, the bikes were a bit top heavy. CZ didn't adopt the system, and continued using dual shocks. A pic of this prototype can be seen below.
In 1971, Suzuki also built a prototype using the Tilkens mono shock, and spent considerable time testing it. In the end, they did not adopt the system either and it would be ten years until they made the switch. The Suzuki prototype is pictured below.
Yamaha was next to be offered the Tilkens Mono Shock system and were quick to develop prototypes. By 1973 the system could be found on their works motocross bikes, and with continued development, the system proved to be superior to anything before it, and for a long time to come. For production motorcycles, the system was offered in 1975, and continued until 1981, when the original monoshock design was replaced with a new design. The pictures below are of the early mono shock bikes. Please see the mono shock page 2, for some final comments.
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