Wheel suspension systems on motorcycles essentially need to perform two tasks – to react very sensibly to loads from uneven road surfaces and rough roads and to keep shocks away from the chassis. This applies in particular in the zero position area when the motorcycle is loaded with the rider's weight plus equipment. Around a third of the total spring travel is used for this. On the other hand suspension and damping should react more strongly during sharp acceleration – including when driving over rough terrain or considerably uneven road surfaces. When spring travel is virtually used up, punching of the spring element should be avoided. We might talk about a progressive spring and damping curve here.
BMW motorcycles with a progressive spring element cater for this requirement profile by the use of progressively wound springs and a diagonally linked spring strut on the paralever. The spring preload can be set conveniently via a handwheel for various rider weights and transport of a passenger and luggage. This is set infinitely via a hydraulic system.
The progressive spring strut is also equipped with a damping system, the damping force of which increases in pressure during compression-stage damping. In addition it allows the damping curve to adjust the compression and the rebound stage to the relevant vehicle type and its application area. The compression may be increased by more than 100 percent while rebound characteristics can be increased by 50 percent.
This patented BMW Motorrad damping system differs significantly from conventional systems in terms of functions. Parallel to the main piston of the damper system, an auxiliary piston works on the inside of the hollow-bored piston rod, which acts as an additional damping system. Both the progressive spring strut and the spring struts without progressive damping enable riders to set the rebound to their own particular riding style and for on-road or off-road use.
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