The present invention relates to improvements in the rear wheel suspension mechanism for motorcycles and like vehicles, advantageously for such motorcycles comprising a driving sprocket at the output of the gearbox, connected by means of a roller transmission chain to a sprocket or gear wheel which is integral with the axle of the rear driving wheel, the axle being journaled in a support related to the oscillating system of the rear wheel. As will be seen in the course of the present specification, the improvements are applicable, as well, to motorcylces provided with a transmission made of a shaft and toothed gearings.
When a motorcycle is made to effect a sudden acceleration (the conventional transmission arrangement from the gearbox output sprocket to the sprocket mounted on the rear wheel axle supported by the oscillating ensemble) a force resolution takes place which tends to raise the vehicle rear wheel, with a corresponding loss of stability during the acceleration.
With the aim of overcoming the above problem, the applicant devised two kinds of transmissions for motorcyles making the subject of the Spanish utility models No. 293,283 and No. 293,573 relating to respective motorcycle transmissions incorporating mechanism intended to obtain, upon a sudden acceleration arising, a force moment on the swing axle of the oscillating ensemble articulated to the motorcycle frame, tending to move the said frame towards the floor over which the motorcycle runs.
It has been observed, in practice, that the force moment obtained with the transmission arrangements masking the subject of the above utility models is excessive and sometimes even of a negative effect. In fact, when the motorcycle runs over an irregular floor, a stiffness effect of the rear driving wheel suspension arises which can lead to a chain rupture.