The shoulder straps should...
The shoulder straps should be mounted to the rollcage so that the portion of the belt that runs between the mount and the top of the driver's shoulders is 90 degrees to the line of his spine.
SHOULDER STRAPS
The purpose of the shoulder straps is to anchor the driver's torso against the seat. Although brevity is necessary with all the belts, you especially want to keep the shoulder straps as short as possible because they are the longest pieces of the system. Any safety harness will allow a certain percentage of stretch, so the longer the belt, the more overall stretch it will allow. To minimize shoulder-belt length, the belts should mount to a rollcage bar almost directly behind the driver's seat and approximately level with his or her shoulder blades (or slightly higher).
The height of the shoulder strap mounts is critical because if they are too low they can actually compress the driver's spine in a collision. But if the mounting position is too high, the driver will be allowed to slide up in his or her seat if the car is overturned.
VanGilder says that the location of the shoulder strap mounts depends on the position of the driver. The mounts should be at a 90-degree angle to the line of the driver's spine. That means if the seat is more reclined, the mounts should be lower. But if the seat has the driver sitting up straight, the mounts should be higher. No modifications are necessary depending on whether the driver wears a head-and-neck restraint such as a HANS Device. Remember that these guidelines for properly mounting your seat and belts could be the difference between walking away from a crash and being carried out on a stretcher. But there is no substitute for talking with the belt and seat manufacturer. The manufacturer you choose will offer resources to help you properly mount your seat and belts.
The newest innovation in racing...
The newest innovation in racing harnesses is a polyester-blend belt-such as this Platinum series harness from Simpson-that is both stronger and more wear resistant than traditional belts constructed from nylon.
BETTER THAN A LEISURE SUIT
It turns out that polyester has a useful purpose after all. Forget that George Jefferson leisure suit hanging in the back of your closet. Polyester is making a comeback in racing. During our discussions with ISP's Kris VanGilder, he mentioned sled testing with upgraded polyester belts versus the standard nylon belts. It turns out that as a material, polyester has properties that are very advantageous in a racing harness system. Simpson Racing Products is now producing new polyester belts in its Platinum line (They are easily recognized because they are silver).
Versus nylon restraints, Simpson says its polyester-blend belts are 20 percent stronger and stretch approximately 9 percent less. They are also more resistant to chemicals, moisture, and abrasion, meaning they are less likely to weaken over time. Moisture resistance should be a big concern for racers because it is easy to wet a belt with your own sweat during a race on a hot summer night, and a nylon belt loses approximately 12 percent of its strength when wet. No matter which brand you prefer, if you haven't already, you may want to consider upgrading to polyester when purchasing your next set of belts.
A head net isn't a replacement...
A head net isn't a replacement for a head support that is a part of your racing seat, but it can help greatly improve the effectiveness of that head support.
HEAD NETS
Another relatively new development is head support nets, or "Sprint Car nets" as many stock car racers call them. Simpson Racing Products says the nets, which are positioned just to the outside of the driver's head supports, help contain the driver's head during a crash and make sure any movement is within a safe zone. In some extreme examples, a driver's head can get caught on the wrong side of the head support, which can be quite dangerous. The large area of the head net keeps that from happening without obstructing the driver's view outside the cockpit too badly.