GMC 2006 Sierra 1500 Pickup Owner's Manual page 368

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
4-56
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
Canada
front axle
W.B. = Vehicle Wheelbase