A good seat system has supports for the leg, pelvis, ribs, and shoulders, as well as the h
In a racing car, the seat is a vital part of the safety system. Seems like a no-brainer, right? Your seat is, first of all, the place where you do your work. It keeps you comfortable during the race and allows you to compete to the best of your ability throughout, no matter the number of laps you're driving. It is also a very important safety device in a crash. The seat influences the occupant's movements in all directions of impact. Or, at least, it should.
Ever hear the term "racing by the seat of your pants?" It translates literally to the feeling a driver gets when the car is in motion. The sensory input starts where the seat is connected to the body. Therefore, the seat in your car should be made to fit you as tightly as possible. If you are sliding around in the seat, you will not be able to feel the car's movement as well as you need to be competitive. Also, if you are loose in the seat, you will be allowed to move relative to the car in an impact. This movement will be acceleration. At some point during the crash it will turn into deceleration, which will increase the injury criteria numbers. This is not desirable.
In today's cars there are two schools of thought with respect to the design of the seat. The first and most common is the aluminum seat that is allowed to deform in an impact to provide "load limiting." The second is the stiff outer shell seat made from aluminum or carbon fiber. A seat that does not deform under impact acts as a rigid outer shell to contain the occupant and a foam inner liner does the load limiting. As one might imagine, this makes the inner liner very important.
Load limiting means it will limit the amount of load the occupant will see at different areas of the body. The theory behind load limiting is to increase the load on the occupant as quickly as possible to an acceptable level, and then ride the occupant down until the end of the event. This will take out the "spikes" in the impact force charts. Spikes in the chart mean unacceptably high levels of force are acting upon the body.
Headrests should be an integral part of any seat mounting process. The padding on this mod
We will first look at the standard aluminum seat. These seats are constructed of bent or formed aluminum sheets. If constructed correctly, the seat is the load limiter in the system. The load still needs to be spread out over the greatest area. This means the seat should support the entire side of the occupant (leg, pelvis, rib, shoulder, and head). Winston Cup racer Jeff Burton uses this type of seat system.
The rigid outer shell seat system is less common because of its greater cost. You will never distort or open up this type of seat system. The inner liner that is form-fit to the occupant absorbs the energy of the crash. You can never run a stiff seat without the foam liner to absorb the energy of the crash. IRL tubs are of this type of construction.
Any seat should have a good kick-up in the front to limit the forward movement of the pelvis, solid leg and pelvis support, rib supports, shoulder supports, and a headrest. The stiffness of each of these parts of the seat should be tuned to the acceptable injury criteria for that part of the body. The pelvis can take the highest load (around 130g's); therefore this is the stiffest area of the seat system. The ribs are the weakest part of the body, so the rib supports should be the least rigid to allow for movement during a crash.
The seat needs to be mounted securely to the bottom and back parts of the seat using large
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.
Once 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.
Note the smooth edges on this seatbelt opening. The openings need to be large enough to no
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.