•  Park the trailer on a level surface. Either place the towing vehicle in park if the trailer is attached to it, or place wood blocks on the front and rear of one set of tires to hold the trailer in place.

•  Place the tip of a measuring tape on the hub face on one side of the trailer axle. Stretch the measuring tape across to the hub face on the other end. This is the track measurement for a trailer axle without tires mounted to it. The hub face is the round metal part on each axle end with the lug bolts on it for mounting tires.

•  Measure the tires width on each end of the axle with a measuring tape. Divide the number by 2 to find the center of the tire. Mark this area on each of the two tires with white marking chalk. Measure the distance from one chalk mark on a tire to the other. Use this process to measure the track on an axle with tires.

related reading: Underslung Suspension  Farm Trailer Axle