The restraint assembly in your race car consists of several components, each with a specific function. The system is built to control a driver’s movement inside the car during a crash, keeping him pinned to the seat and allowing him to ride the crash down to acceptable limits of force.
This article will show you mounting methods and usage procedures to make your car as safe as possible and give the driver a better chance of avoiding serious injury in the event of a crash.
The Seat Belt System
The shoulder harness is a belt assembly (one strap for each shoulder) intended to restrain movement of the upper torso and shoulder regions. An optional cross-strap across the chest, called a sternum strap after the bone it bisects, can be used to hold the shoulder harness together. The sternum strap was initially designed to spread belt-tension loads across the chest and include the sternum as a load-dispersing member, but tests have shown it is limited in its effect in a high-deflection (head-on to 30-45 degrees) crash. During side impacts, however, its effectiveness in equalizing shoulder belt loading is increased. There are also questions regarding the mounting of the sternum buckle, including the fact the buckle is close to the driver’s chin and could be an obstacle to exiting the car quickly following a crash.
The lap belt restrains movement of the pelvis. We will detail the proper mounting methods later in this article, but angles and placements of this belt are very important. If it is used incorrectly, it can cause serious damage to internal organs.
The anti-submarine strap(s) prevents the pelvis from slipping forward from under the lap belt in the event of an accident. The anti-submarine belt is where the terms five-point and six-point belts come from. The five-point belt system uses a single vertical strap that attaches the lap and shoulder belts to the chassis and helps hold the other belts from rising up on the driver’s body.
The six-point anti-sub belt is an upside-down V, which still attaches to the lap and shoulder belts but mounts to the chassis in two separate, spread locations. This anti-sub belt placement helps to better control the movement of the driver’s lower torso. In fact, Ford Motorsports, seeing the benefits of the six-point system, is encouraging its drivers to utilize the six-point belts. PPI Motorsports’ NASCAR Winston Cup team has experimented with a seven-point system using both the single vertical strap and the upside-down V. This system controls the upward movement of the belts and offers improved control of the driver’s lower torso.
The buckle, which hooks the belts together, has a quick-release mechanism in case of an emergency situation. There are three types of buckles to choose from: latch/lever, turn/push and cam lock. All three can be opened in one or two motions. In case of an emergency it is better to have a mechanism that is both simple to unlatch and will stay secure under all other stresses. Mechanisms with all-metal components should be mandatory. Any type of mechanisms with plastic parts or items that would easily warp or melt should be discarded.
A restraint assembly also utilizes two types of hardware: adjustment and mounting. The adjustment hardware is used to change the length of the individual straps to fit the driver. The mounting hardware secures each strap to the chassis. It is of critical importance to use the manufacturer’s recommendations for mounting locations and hardware, as well as the sanctioning body rules on what is required.
Inspect Your Belts Regularly
Restraints must be maintained, inspected and replaced or re-webbed every two years because they degenerate over time and from exposure to the elements. Prolonged exposure of seat-belt webbing and thread to sunlight can cause degradation of the fibers and loss of restraint integrity.
The webbing used in motorsports restraints is typically made with DuPont Nylon 6-6 or a similar product. According to data derived from tests on the nylon webbing material, the strength of typical webbing can be cut in half with only one year’s exposure to outdoor weather and sunlight. After two years of this exposure, the strength of the webbing can be reduced to 20 percent of its original strength.
With this kind of rapid deterioration, it is obvious that replacing the webbing every two years is essential to driver safety. Old and weakened belts could easily snap under the loads imposed upon them in a crash. A belt system that “looks” good enough is not worth your safety. By comparison, a new set of belts is cheap compared to the possible damage an old set could cause.
Proper Installation Is Vital
The effectiveness of a restraint assembly is also influenced by attachment techniques. The principal precaution for installing the mounting hardware to the vehicle is to minimize bending stress in the mounting brackets. This is achieved by making sure the belts pull from a straight angle against the hardware. The assembly should be installed so the straps do not rub against any surface that can cause the webbing to fray. The anchoring mechanisms should also periodically be checked to see if they have become loose or weakened.
Proper installation of the restraint assembly also means achieving the correct fit to the driver. Belts should be as short as possible to reduce stretching for better control of driver movement. How the belts run through the seat while the driver is seated is also an important concern. With the driver seated and the belts tight, none of the belts should be in contact with or laying across their access holes in the seat. If the belts bend at a different angle because they lay incorrectly across the access hole then that also affects the way the body is restrained and could promote chafing and fraying during a race.
The attachment points must provide the optimum geometry to minimize movement of the belts. Lap belts perform best when they act at an angle between 45 and 55 degrees relative to the longitudinal axis of the vehicle. This angle permits the lap belt to react to the upward pull of the shoulder harness. A system installed with a shallow belt angle permits the shoulder harness to pull the lap belt up off the pelvic area and into the abdominal region, which greatly increases the chances for internal injury.
The end attachments of the shoulder harness must also be installed at appropriate angles. The ideal position is anywhere between five degrees below and 30 degrees above the driver’s shoulder.
If the upper attachment point falls significantly below the driver’s shoulder, then a spinal compression injury is likely to occur. In an accident, the shoulder belts pull down and back on the torso as they resist the forward motion of the driver. The resultant restraint force compresses the spinal column and will add to the stresses in the spine already caused by the force of the crash impact.
In the opposite situation, if the trailing ends of the harness are too far above the shoulder (greater than 30 degrees), then two problems can occur. First, tension in the shoulder harness is increased and undue stress is applied to the harness and its structural attachments. Second, excessive angle will cause excessive motion. If the harness belts are too far above the shoulder, they will provide little resistance to forward motion of the driver’s upper torso. The result is an impact with the steering wheel and the possibility of neck injury. The shoulder straps should also be three to six inches apart behind the driver’s neck to prevent slippage off the shoulders.
The reliability of a restraint system is greatly affected by the way it is installed. It is imperative to follow the installation instructions provided by the seat-belt manufacturer. Also, the necessity of replacing or re-webbing seat belts every two years cannot be more important.
There are many considerations in the safety of a race car driver. The ones that are the most personal to the driver are the seat and seat belts. As with the parts that make the car go faster, the parts that keep the driver safe should be the best and newest and should be checked and replaced at definite intervals.
