GMC Sierra Classic 2007 Owner's Manual page 412

United States
In order to calculate the amount of weight any
front accessory, such as a snow plow, is adding to
the front axle, use the following formula:
412
Canada
(W x (A + W.B.)) /W.B.= Weight the accessory is
adding to the front axle.
Where:
W = Weight of added accessory
A = Distance that the accessory is in front of the
front axle
W.B. = Vehicle Wheelbase