Belt Up! - Willans Harnesses

As I navigate for a number of different drivers, people ask me how I can bear to trust a new driver. Because you can never expect not to crash in motorsport it is vitally important for me to check how the car is set up and how it will help me to walk away from an accident. (The sanity of the driver is also important but that's another article...)

I will be contacting a number of different manufacturers of safety equipment over the next few months, asking them how their product works and what I should be looking for when I get into a car for the first time. I hope that the answers will be of interest to other club members, including those who are buying a second-hand car or even building one from new.

For this article I wrote to Stockbridge Racing, makers of Willans Harnesses, to discuss seat belts.

How should the belts be mounted?

Figure 1 shows the general set-up of the harness. All the straps should run directly to their anchorage point with no obstruction or deviation. Straps should not be twisted when in use. All installed strap lengths should be kept as short as possible for the best performance of the harness.

The tail straps should run between horizontal and 20% to horizontal and should be as close to the shoulder as is practical (figure 2). During a crash the webbing is designed to stretch. This is desirable as it can help to reduce the peak forces imposed on you, but excessive stretching can be a problem as your head could hit the steering wheel or roll cage. Anchoring the shoulder straps to the cage directly behind the seat rather than to the rear seat pan or parcel shelf can reduce the total amount of stretching by approximately one half. Anchoring these straps too steeply downwards can put a load on the back of the seat which could cause it to snap.
The lap belts must run vertically downwards and not forwards or rearwards of the hip joint. They should be anchored symmetrically either side of the wearer about 20" apart. The belts should pass through slots in the seat and not over the seat. These slots should be in line with the free path of the belts and their edges should be well rounded and/or taped to prevent damaging the webbing.
Twin crotch straps should be mounted to your rear and 10"-12" apart. These should also pass through the seat rather than over it.

Figure 3 shows how the hook bracket and eye bolt should be positioned. The lap strap hook end brackets must be connected with the open part of the hook forwards and there should be split pins securing the hook bracket keepers.
The lap and shoulder anchorage points should each be capable of accepting a static load of 1590kg (so you should be able to pick the car up using one of them). The crotch strap anchorage point should accept a load of 770kg. When vehicle manufacturers' anchor points are not used, reinforcing plates and washers should be used at the anchorage points.

How should I adjust them?

The lap belt should go across your hip bone and never across your abdomen. Belts which are worn too high sometimes produce very serious internal injuries in crashes that should otherwise have produced no injury at all. The shoulder strap adjusters should be positioned on the breast bone (see figure 1) - adjust the tail strap length to set this correctly.

The crotch strap is often difficult to adjust once the seat is in place. It should have been set up to be as tight as is comfortable with the lap belts fully tightened.

To adjust the harness, slacken off the lap and shoulder belts and sit in the seat. First adjust the lap straps so that the buckle is central and the straps pass over the bony part of the hip/pelvis and are as tight as is comfortably possible. Remember that any springing in a car seat will compress if you are bumped downwards which will slacken the lap strap. Now tension the shoulder straps.

In use the belts should always remain as tightly fastened as possible, so keep re-tightening them during an event. Even slightly loose belts dramatically increase the chances of injury during a crash.

And under no circumstances should the harness be used without both shoulder straps and both lap straps connected.

What sort of belts are recommended?

For comfort, shoulder straps should be as wide as possible, with three inch webbing now being readily available. Wide shoulder straps spread crash loads against your chest over a large area and can reduce the level of injury. It is not uncommon for drivers to have black and blue areas around their shoulders following a crash because of the belts pressing against them. Wider belts reduce this pressure on you. However, it is 'horses for courses', as some people find the presence of wider adjusters uncomfortable.

Twin crotch straps should also be used (some people find a single strap very uncomfortable). These are primarily intended to ensure that you cannot slide out from under the seat belts during a frontal impact but they do more. They are extremely important in helping to keep your belts tight. They also hold the lap belt down so that it has a better chance of staying correctly positioned on the hip bone.

For International-grade events you now need belts homologated to FIA standard 8854-1991 or 8853-1985 and they must have a label on showing this.

What are the danger signs with belts?

Seat belts require very little maintenance following installation but you should inspect them for fraying and check the secureness of the mounting points. Check that the webbing has not come into contact with grease, petrol or battery acid, and that it has not been dyed or bleached. And make sure that the release mechanism works smoothly.

Check that the belts haven't been re-used after a heavy crash. The webbing is designed to stretch in a crash to cushion the impact. However, if it has been over-stretched it will no longer be so elastic and so it may either not cushion you enough or it may even snap. In addition, a heavy impact may produce minute cracks in the metal parts of the harness which would make the whole harness effectively useless in the next crash. This is why Willans will not re-web harnesses.

This article is based on information kindly supplied by Stockbridge Racing but because I have edited it the views expressed are not necessarily theirs.

Catherine Phillipson