California Code, Vehicle Code - VEH § 35601

The gross weight of any vehicle and load resting upon any metal tire in contact with the roadway shall not exceed 500 pounds upon any inch of the width of such tire but this limitation shall not apply to traction engines or tractors, the propulsive power of which is not exerted through wheels resting upon the roadway but by means of a flexible band or chain, known as a movable track, when the portions of the movable tracks in contact with the surface of the roadway present plane surfaces.