This is just one accepted method for figuring axle placement on a gooseneck trailer. This method should only be used if you will be hauling evenly distributed loads. Measure the total length of the trailer box(A). The centerline of the axles should be placed 2/3 of the distance towards the rear of the trailer. If the measurement of the trailer box (A) is 30', the centerline of the axles (B) should be 20' from the front of the trailer box.