Idaho Code § 49-1003: Speed limits for vehicles regulated according to weight and tire equipment.

It shall be unlawful to operate any vehicle equipped with other than pneumatic tires on a highway at a rate of speed in excess of twenty (20) miles per hour for vehicles having a gross weight of not more than ten thousand (10,000) pounds, and twelve (12) miles per hour for vehicles having a gross weight of more than ten thousand (10,000) pounds.