The recommended gear ratios, or axle ratios, for Ford trucks are 3.31, 3.55, 3.73 and 4.30 axle ratio. To choose the right gear ratio consider factors such as terrain, weight of load on truck, trailer weight, maximum speed of truck and size of tires.
As a general rule, the numerically lower gear ratio of 3.31 provides less torque and is used when load on truck is less thereby improving fuel efficiency. If vehicle has high rate of speed with light load, a mid gear ratio of 3.55 or 3.73 is recommended. Additionally, the numerically higher gear ratio of 4.3 provides increased torque and improves acceleration from low speeds. This gear ratio is recommended when the load on the truck is high and the road is steep.