Patent ID: 7232130

Claim:
A rear drive assembly for a snow bicycle, comprising: a body adapted to be supported by an axle which rotatably supports a rear wheel of a bicycle, with a drive sprocket of the wheel positioned outside of the body such that it is accessible to an external drive chain; an upper arm rigidly affixed to and extending upwardly from the body, the upper arm having a remote attachment end; a lower arm rigidly affixed to and extending at an angle downwardly and rearwardly from the body, the lower arm having a fixed angular relationship to the upper arm, the lower arm having a remote attachment end; a track tensioning and guide assembly positioned at the remote attachment end of the lower arm, the track tensioning and guide assembly including a first arm having a first end and a second end, a second arm having a first end and a second end, the first end of the first arm and the first end of the second arm being pivotally mounted for pivotal movement about a common horizontal pivot axis, three track engaging tensioning and guide wheels being arranged in a triangular configuration with a first wheel rotatably mounted at the first end of the first arm and the first end of the second arm, a second wheel mounted at the second end of the first arm and a third wheel mounted at the second end of the second arm, means being provided to bias the second end of the first arm and the second end of the second arm away from each other to exert a tensioning force upon a track extending over the rear wheel of the bicycle and over the three track engaging tensioning and guide wheels of the track tensioning and guide assembly, the remote attachment end of the lower arm being attached to the second arm to force said first wheel and third wheel into ground contact; and an extendible and retractable attachment member positioned at the remote attachment end of the upper arm, the attachment member being adapted for attachment to a seat post of a bicycle, the extendible and retractable attachment member controlling movement of the upper arm toward and away from the seat post, such that as the bicycle begins to ascend a slope the attachment member retracts to maintain the track in ground contact and as the bicycle begins to descend the slope the attachment member extends to maintain the track in ground contact.