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240 Landmarks of Japanese Automotive Technology
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240 Landmarks TopChassis > Monocross suspension
 Monocross suspension
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1. Increased rear wheel travel: A shock absorber was set under the fuel tank, increasing rear wheel travel from 120 to 160 mm. This length was increased every year by 20 mm, finally reaching 300 mm, although tests were conducted up to a maximum of 340 mm. Because of the increase in wheel travel, the degree of freedom of the suspension spring increased, the initial load became large and it became possible to set a small spring constant.
2. Increased degree of freedom in selecting damping characteristics: In addition to a conventional oil damper, a high-pressure nitrogen gas charged accumulator was set. This expanded the range of damping characteristic selection, and consequently, soft damping characteristics could be achieved.
3. Improved rigidity of frame and swing arm: The swing arm that supports the rear wheel was changed from the conventional flat shape to a three-dimensional form based on a triangle, which dramatically increased its rigidity. The front end of the shock absorber was fixed to the head pipe portion, which has the highest rigidity in the frame. In this structure, the absorber receives the load from vertical stroke of the rear wheel, enabling extremely high overall rigidity while riding. This increased rigidity was particularly effective for motocross bikes that are ridden on rough roads. Later, the structure was applied to road racers and helped improve riding characteristics.
4. Prevention of lateral motion by integrated shock absorber: Conventional two shock absorbers on the right and left may cause lateral motion when the loads applied to the right and left units are different, such as when riding on slopes and cornering. However, in the case of the monocross suspension, loads are applied to one shock absorber, preventing lateral motion.
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Storage location:YAMAHA COMMUNICATION PLAZA (2500, Shingai, Iwata-shi, Shizuoka-ken 438-8501)
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Year manufactured:1974
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Manufacturer:Yamaha Motor Co., Ltd.
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Classification:Mass-production part
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Current status:Operational
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Model
Familiar name:Monocross suspension
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Model / Weight
Company name:Yamaha Motor Co., Ltd.
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Location:Communication Plaza
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Installation vehicle:YZ250M
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Year of manufacture:1974
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Designed by:Yamaha Motor Co., Ltd.
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Structure, type, means, method, etc.:・Conventional motorcycles had a rear suspension with a shock absorber on both sides of the tire (2 shock absorbers in total). But the structure of the monocross suspension was completely different with one shock absorber set at the vehicle center under the tank.
・The shock absorber consisted of 3 portions: a suspension spring, oil damper, and accumulator.
・The accumulator was separated into a damper oil chamber and a gas chamber by a rubber film, and high-pressure (20 hPa) nitrogen gas was contained in the gas chamber as an inert gas.
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Function, effect, etc.:・A damper oil viscosity buffer and the air cushion effect were both used.
・The rear swing arm had a triangular three-dimensional structure with high torsional strength, and vertical motions of the rear axle were converted to longitudinal displacement. The lever ratio from the swing arm axis was set larger than a conventional type to increase the travel of the rear wheel.
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Technical overview:・The rigidity of the whole body when ridden was dramatically increased. Moreover, the increased rear wheel travel remarkably improved off-road running performance.
・This technology was employed for high performance street vehicles, and their cornering and straight line vehicle stability at high speeds were substantially improved.
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Points of interest, topicality:In 1973, factory racers installed with the monocross suspension appeared in the All Japan Motocross Championship for the first time. It dominated the top three places in both the 125 cc and 250 cc classes. In particular, in the highlight jump sections of motocross races, jumps by bikes using this monocross suspension were so long that it came to be called the "flying suspension".
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