Correct placement of the trailer axle can ensure safe and easy towing for your construction and industrial hauling needs. Follow the 60/40 rule for placement. Measure the length of the trailer cargo box or platform, not including the trailer tongue. Then, multiply this length by 0.4. The result is the distance from the center of the cargo box to the center of the axle. For example, a 10-foot box is 10 x 0.4 = 4. You would mount the axle so that the axle center point is 4 feet from the rear of the trailer.