The seat system must include strong shoulders and a headrest. These two need to be connected together to ensure that they move at the same rate. The headrest should have a minimum of 3 inches of energy-absorbing foam on each side. I have had very good overall performance with dual-layer designs, softer visco-elastic foam on the inside for comfort and low-speed performance, and a stiffer inner layer for high-speed energy dissipation.
Mounting PointsOnce you have a good seat system, the components need to be mounted securely. They need to be mounted only on the bottom and back surfaces, never on the sides. You must use large fender washers on aluminum seats. The upper part of the seat needs to have four bolts, two in the lower back and two in the front leg portion of the seat. I use 31/48-inch bolt (Grade 5 or higher) in all of my sled testing. The headrest needs to be secure and mounted to the rollcage and the seat back in at least two points.
Seatbelt openings need to be large enough to not obstruct the normal routing of the belts and allow for the forward movement of the belts without contacting the edges of the openings. The belts should never change direction through a seat opening. The belt openings should be radiused and smooth. A trim edge can be used for smoothing the edges.
I will speak to more specific information on the headrests and shoulders in future articles, but this should give you enough information to work with your seat builder to get the seat you need for your application. Remember, no matter what series you run in, the concept of the safety system is the same: It all works together to protect you in a crash.
Trevor Ashline, a restraint-system engineer, developed the Hutchens Device for racers and is currently the safety advisor for BSR Products, Inc. Ashline 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.