Build Your Own Seat Insert

Boxing heavyweight world champion Mike Tyson once said, “Everyone has a plan until they get punched in the mouth.” I’ve been punched in the mouth and it turns out Iron Mike was absolutely correct. Besides a schoolyard scuffle during my youth, I have also been figuratively punched in the mouth while inside a racecar. Those impacts were unexpected and violent. And those impacts made me realize very quickly that my driving seat setup wasn’t as good as I had “planned.”

Containment racing seats, similar to the child seats we carefully strap our children into to go to school, are designed to protect us during a collision. Many of us forget that. We simply think of the seat as the piece that connects us to the racecar so we can see over the dashboard and instantly feel if the car is slipping underneath us. Yes, the seat does do those things, however, its main purpose, and what it was engineered and designed for, is to save you from injury during a collision.

Allow me to nerd out a bit on the physics involved with this thing called “occupant kinematics,” or your body’s movement within a vehicle during a collision. There are three parts to a collision. Part 1: Your car hits the wall (this is bad). Part 2: You hit parts inside the car (this is extremely bad). Part 3: Your internal organs collide with the inside of your body (this can be fatal). Automotive engineers and physicians realized, after a massive death toll on our public roadways for decades, that a metal dashboard and sturdy vehicle frames may help the vehicle survive a crash, but the occupants won’t be around to see those cars get repaired. The occupants will be six feet underground. From this realization is where we got the crash standards designed in the vehicles we have today. The idea is the car takes the brunt of the collision and we, the humans, “ride down” the collision. Cars, after all, are easily replaced.

Ride down is, simply, time. Most racecar drivers repeatedly slow from 100 miles per hour to zero during a race. However, we do that over 6 seconds under braking, which our frail human bodies can handle. If we slow from 100 miles per hour to zero when we hit a wall in just 30 milliseconds, we will not survive. Time can save your life. How you gain that time is by two parts. The first part is to have the vehicle crush during the collision – let the vehicle take the damage, not your body. The second part is to ensure you are securely attached to the vehicle so you, in the occupant seat, can enjoy the ride down of the vehicle’s crush — and not hit stuff inside the car. If you are not securely attached to the seat, you will then accelerate relative to the interior of the vehicle — the dashboard stops and you continue toward it — and that impact can injure you or be fatal. The better you are attached to the vehicle, the better your chances of walking away unscathed from a big hit. That is why your harnesses and the fitment of your containment seat are so crucial.

NASA Norcal racer Eli Cronbach, who runs Service Motorsports, was gearing up for an enduro and needed to create foam inserts for his Mustang. He wanted to help his different-size drivers fit better in the seat for safety and for his height-challenged drivers, to help them actually be able to reach the gas pedal. He had each driver on his four-driver team make their own seat mold. He used TAP Plastic’s X-30 polyurethane foam which will expand up to 30 times its original fluid volume. It comes in two parts which are mixed together one-to-one. This foam is often used by people creating molds or watercraft — it floats — and it works great for foam inserts for racing seats.

Some painter’s tarps and garbage bags are the perfect items needed for containing the foam after it is mixed and begins to expand. Mix the X-30 and pour it into the garbage bag. Have the specific driver in an old racing suit sit in the seat with the garbage bag filled with the expanding foam under him or her. If you want a little riser in the base of the seat, or you need the seat to push you away from the back of the seat allow the foam to set for about five minutes before you sit in the seat. The working time for the polyurethane foam is about 10 minutes total.

Some people do their seat molds in separate sections, the base, the lower back, and then the upper back. The three pieces will weld together when put into contact with a new mix of polyurethane foam. While the driver sits in the seat and the foam sets, they will feel some heat as the polyurethane foam works but it isn’t so hot that it will burn you through your suit. Pro tip: Don’t let this stuff get in your hair. My brother, Randy, had to endure a rough and painful haircut after some of the mix got in his hair.

This stuff sets up fast. There is no time to dilly dally. You have a total of 10 minutes to work with this material. Within 15 minutes the foam is hard enough you can begin cutting holes in it for things like a sub belt or to trim the edges near the shoulders. A sharp knife, like one you would carve a pumpkin with, works perfectly for this job.

A gritty sandpaper block (around 50 grit) will make quick work of smoothing out the foam seat mold. There will be minor bumps and holes from air bubbles or crinkles in the garbage bags during the setting time. This can be easily taken care of with some elbow grease.

This is a do-it-yourself project that will help you to be a better driver in your own car because it ensures you fit in the car better. Having a good fitment with a seat will ensure you don’t get fatigued as quickly in a racing car. With correct fitment, you are using your arms and legs for inputs with the wheel and pedals, as opposed to trying to keep you from sliding within a seat. This is an inexpensive way to be safer and faster. Win-win!

The final project was a success. Each driver on Eli’s endurance racing team had their individual seat mold, which would help them fit inside the car better to enjoy better ergonomics and, more importantly, allow them to be one with the seat, which is one with the car to avoid injuries if a collision were to occur. Great work Service Motorsports!