It's a Team's Life

Montana DOT

Bob was driving and the scale was open in Montana, as he pulled onto the scale he stopped and waited for a green light.   Soon the scale master stepped out to talk to Bob about the wide base single tires.   Bob could see on the scale readout that this axle weighed 17,200 lbs. which is not a problem.   The scale master asked if Bob was aware of the weight limitations of this tire in the state of Montana.

Bob told him no and then the scale master proceeded to give us an education about the laws in Montana for commercial vehicles.    As he was performing a level one inspection he talked about an odd law in Montana concerning wide base single tires. The state of Montana allows 500-lbs per inch of sectional width which is figured by using the information on the sidewall of the tire.   For example a 445 50R 22.5 is figured by taking the first number 445/25.4 X 500 X 2 = 17,500 lbs. per axle.  Divide 445 by 25.4, which is converting the metric designation on the side of the tire to inches.   Then take the result 17.519 times 500, which is the pounds per inch allowed, then times two and you will end up with the legal axle weight.  

445/22.4  *500 *2 = 17,519

When we crossed the scale we had our pusher up and our drive axle crossed the platform weighing 17,200 lbs. and we were empty.   We normally do not put our pusher axle down unless we are carrying 2000lbs of freight, as we are legal in most states.  

This is one of those quirks where the unknowing can get a hefty fine if not careful.  

Allowable load per inch width of tire Montana