Harness sets are designed for use with a sub-strap. Use of harness set without sub-strap can cause serious injuries. The sub-strap holds the harness buckle in place over the pelvis area and helps prevent the driver from sliding down in the seat. The pelvis area can withstand 5000 pounds of load before serious injury where the abdominal area can withstand only 800 pounds of load so it is very important that the harness remains in the proper location. Proper installation is very important. Adjustment length- shoulder: 26 inch - 50 inch/ Pull-up lap: 38 inch - 80 inch /pull-down lap: 38 inch - 67 inch / sub-strap: 7 inch - 25 inch.