2005 California Vehicle Code Sections 35600-35601 Article 2. Tire Limits

35600.  The gross weight upon a solid tire upon a vehicle shall not
exceed 600 pounds upon any inch of the channel base width of such
tire.
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.