Chevrolet 2011 Silverado 2500 Owner's Manual page 419

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
W.B. = Vehicle Wheelbase
For example, adding a 318 kg
(700 lb) snow plow actually adds
more than 318 kg (700 lbs) to the
front axle. Using the formula, if the
snow plow is 122 cm (4 ft) in front of
the front axle and the wheel base is
305 cm (10 ft), then:
W = 318 kg (700 lb)
A = 122 cm (4 ft)
W.B. = 305 cm (10 ft)
(W x (A + W.B.))/W.B. =
(700 x (4 + 10))/10 = 445 kg (980 lbs)
So, if the front axle reserve capacity
is more than 445 kg (980 lbs), you
could add the snow plow without
exceeding the front GAWR.
You can add heavier equipment
on the front of the vehicle if you
compensate for it by carrying fewer
passengers, less cargo, or by
positioning cargo toward the rear.