FORD 2008 F-550 v.4 - Manual (Page 237)

The appropriate loading capacity of your vehicle can be limited
either by volume capacity (how much space is available) or by
payload capacity (how much weight the vehicle should carry). Once
you have reached the maximum payload of your vehicle, do not add
more cargo, even if there is space available. Overloading or improperly
loading your vehicle can contribute to loss of vehicle control and
vehicle rollover.
Example only:
2008 F-250/350/450/550 (f23)
Owners Guide (post-2002-fmt)
USA (fus)
Tires, Wheels and Loading
237