Patent ID: 8075069

Claim:
A combination of a drive tumbler and a track comprising: a) a track made of a plurality of connected track shoes each having a ground engaging surface and an inside surface opposite the ground engaging surface, the track further having a plurality of driven surfaces, the track being wrapped around the drive tumbler so that a plurality of the shoes are in contact with the drive tumbler; and b) a drive tumbler having an axis of rotation, comprising: i) a plurality of drive surfaces, at least one of which engages one of the driven surface on the track; and ii) a circumferential rim surface that includes a plurality of shoe contact surfaces that each contact the inside surface of one of the track shoes that are in contact with the tumbler; wherein the shoe contact surface has a shape such that a line normal to the tangent of the shoe contact surface does not pass through the axis of rotation of the drive tumbler, thereby allowing the shoe contact surfaces on the rim of the drive tumbler to transmit a tractive force to the track.