Editor's Note: Trevor Ashline, a restraint-system engineer, developed the Hutchens Device for racers and is currently the safety advisor for BSR Products, Inc. He is a graduate of Rochester Technical Institute in New York, and after a career in passenger-car safety analysis, has specialized in racing safety for the past two years.
In his motorsports capacity, Ashline has overseen more than 60 sled tests of stock cars, and designed and developed seats, headrests, seatbelt systems, and head restraint systems. This is the opening installation of an exclusive monthly column for the Circle Track Saturday-night racer dealing with safety systems.
Have you ever wondered if your safety equipment was adequate? When you tighten the seat and the seatbelt anchor bolts, are you questioning them? I am here to help the race car driver understand what happens when you crash. With this understanding, you will be better able to make informed decisions about your safety system.
Your safety system consists of everything around you in the cockpit. Your system needs to be well thought-out. Most of the differences between a good and a bad safety system are in the details. Everyone has to mount and adjust the seat, belts, padding, steering wheel, and personal restraint system. If you or your crew knew that they could change the placement of your belts slightly and add a few more bolts to the seat system (which we'll take on in another installment) to make your safety system better, wouldn't you? In many cases, additions of energy-absorbent foam can also help control the movement of the occupant in addition to the belts and the seat.
Correct mounting is the key The easiest way to increase your system's effectiveness is to have your seatbelt system mounted correctly. The seatbelts should always be mounted per the manufacturer's instructions. A good rule of thumb for an upright seating position (the angle of the seat back is determined by the type of vehicle it is installed in) is to have the lap belt mounted at an angle of -40 degrees to -60 degrees down from a horizontal line from the "H"-point (center of the driver's hip). The six-point mount should be as short as possible and mounted in back of the chest line. The chest line is a straight line from the chest through the buckle position. The upper torso (shoulder) belts need to be mounted as short as possible at an angle of 0 to -10 degrees from the top of the shoulders to the bars behind the seat or to the brackets provided by the manufacturers, depending on the application.
Six-Point Harness I also highly recommend a six-point belt system that mounts wide at the lap belt buckle. New hardware is available to accomplish this even with the standard latch-and-link buckle. The idea of the six-point system is to effectively wrap the pelvis and to limit the amount of movement. The key to all restraint is the pelvis. Federal government safety studies indicate the pelvis can take loads up to 130gs, compared to 80gs for the chest and 60gs for the head. If you can control the pelvis, it is easier to control the movement of the torso and then the head and neck. A properly mounted lap belt and six-point harness can reduce the pelvic movement by 40 to 50 percent over a standard five-point system.
The lap belts should be mounted as close as possible to the occupant to reduce belt length and insure quick belt response in side and angular impacts. The mounting angle mentioned earlier (-40 to -60 degrees) will help the lap belt stay on the pelvis during the event. This, not "dumping" (which occurs when the free end of an adjustable belt is not in line with the loaded end of the belt and can shear the webbing), is the main reason for mounting the lap belts more forward in the car. When the lap belts are mounted farther back, the angle of the belt is low. The buckle will easily rise into the abdomen when the driver starts to "sub under" in a crash. With the forward mounted belt -40 to -60 degrees from the H-point, it is harder for the buckle to rise off the pelvis and into the abdomen.
These are just a few ideas to help with belt installation. Next month, we will take on another topic as well as answer your questions concerning racing safety. Send your safety-related questions to firstname.lastname@example.org. Recognize that more research about racing safety is being done now than ever before. This testing is resulting in advancements that could help you in the event of a crash.
The proper angle for mounting...
The proper angle for mounting seatbelts is the top of the shoulder and at the H point of the occupant's hip. Pay particular attention to the instructions provided by your belt manufacturer.
These are the proper mounting...
These are the proper mounting points for both five- and six-point harnesses.