Measure the total length of the box(A) and divide that dimension by 2 to find the centerline of the trailer box. For each foot of total box length(A) move the centerline of the axles(B) toward the back of the trailer 1 inch from the centerline of the trailer box. That axle centerline is where you will attach the middle spring hanger. Be sure to position front and rear spring hangers according to manufacturers specifications. Be sure to pull diagonal measurements from the middle spring hangers to the coupler to be sure that your trailer will track straight. Example: For a 12' trailer box(A), the centerline of the trailer box is 6'(12' / 2 = 6'). Since the trailer box length is 12', the centerline of the axles will be 12" (or 1') towards the rear of the trailer from the centerline of the trailer box(1" per foot on 12' box length). So the centerline of the axles will be 7' from the front edge of the box. For a trailer with excessive tongue weight, you can cheat as much as 10-15% toward the centerline of the trailer box to
compensate for the tongue weight. Be careful not to over compensate because without proper tongue weight, your trailer can become a mobile disaster for you and anyone else on the road. This method should only be used if you will be hauling evenly distributed loads.