[Bo Wallen]

I like this explanation or what it's called....Wheelbase
Manufacturers advertise wheelbase according to the distance from the center hub of the steer axle, to the center-point between the two rear wheels on a three-axle truck. So, stick a ruler vertically in the ground right in between the two rear tires, and measure from there to the steer axle. However, possibly more relevantly, officials at the DOT take literally the simplistic technical definition of "wheelbase," which is "the distance between the front steering hub and the rear wheel hub." So, when it comes time to pay tickets for bridge length permit violations, wheelbase measures from the center of the last wheel. Otherwise, advertised wheelbase is from the center of the two wheels, or from the hub of the center axle on a four-axle truck.