Legal vehicle weight
Gross vehicle weight (GVW) for a vehicle or a vehicle combination is determined by an overlapping set of three criteria: tire size, axle weight, and the weight table. The lesser of any one of the criteria will govern the weight of any axle or axle group
Maximum gross weights - Wheelbase and axle factors
No vehicle or combination of vehicles shall operate upon the public highways of this state with a gross load on any single axle in excess of twenty thousand pounds, or upon any group of axles in excess of that set forth in the following table, except that two consecutive sets of tandem axles may carry a gross load of thirty-four thousand pounds each, if the overall distance between the first and last axles of such consecutive sets of tandem axles is thirty-six feet or more.
The legal weight table RCW 46.44.041 according to state law.