GMC 2010 Sierra 1500 Crew Cab 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.
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