GMC 2007 Sierra 1500 Pickup Owner's Manual page 418

Q:
What is front axle reserve capacity, and
how do I calculate it?
A:
Front axle reserve capacity is the difference
between your front Gross Axle Weight Rating
(GAWR) and the front axle weight of your
vehicle with full fuel and passengers. Basically,
it is the amount of weight you can add to your
front axle before reaching your front GAWR.
The front axle reserve capacity for your vehicle
can be found in the lower right corner of the
Certification/Tire label, as shown.
United States
418
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:
(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
Canada
W.B. = Vehicle Wheelbase