Driver's Seat Ergonomics - Unfair Takes A Seat

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From the August, 2011 issue of Super Chevy / By John Parsons / Photography by The Author
Editor's Note
This month's story about the fabrication and ergonomics of our Project Unfair's pedals, seat, and steering column takes place back at II Much Fabrication in John Parsons' small shop. --Jim Campisano
With the Coast Chassis Design rollcage installed, Frank Serafine (of Prodigy Customs) and I needed to get the ergonomics of our '69 Camaro in order. Since we've moved the firewall, raised the floor, made a custom transmission tunnel, and installed a rollcage, this is no simple bolt-in deal. Getting all the controls into comfortable reach and incorporating proper safety methods is no easy matter. The relationships between the seat, steering wheel, and pedals are not that obvious and something most of us take for granted when we jump into our factory-built cars. With all the changes to the surfaces in the driver's area, we had to start our positioning of the driver's controls at the beginning.
The pedal/steering wheel/seat arrangement is a bit interdependent, but you have to start somewhere. In general (with an inch or two of tolerance), the most ergonomic performance driving position has the seat back tilted at least 15 degrees, with the steering wheel centered with the seat. The best racing position has the driver's hands at the 9-and-3 position and close enough so that the either arm can be extended over the top of the steering wheel with the wrist resting on the top of the wheel without the shoulders coming away from the seat.
From there, the pedals should be positioned with the brake pedal centered under the column, and the clutch pedal between 4 and 5 inches away (measured from the centers of the pedal pads). It's often more comfortable for the clutch to be an inch or so higher than the brake. We're going to road race this car (a lot!), and that means the throttle needs to be reachable while braking for heel-toe downshifts. That will require the throttle to be within 4 inches of the brake and about midway through the brake pedal's travel. The idea is to be able to blip the throttle with the side of your foot while maintaining threshold braking with the ball of your foot. The brake and clutch pedals should be largely controlled by your legs, while the throttle is controlled by your ankle, which is why the brake and clutch pedals are closer to you than the throttle.
That's a lot of interdependent variables, without even taking driver preferences into play. The chances of getting all this right the first time are pretty slim. Frank and I are about the same height with similar body types, but we still need some adjustability in order for the two of us to be comfortable driving the car. Most factory cars take that into account with adjustable seats, but that's not an option for us since the six-point Schroth Racing harness has very specific mount points. The only solution, since the seat is fixed into place, is to make the pedals adjustable.
We'll be using Cobra Suzuka Pro seats. (The Pro means "middle-aged man" as it is 2 inches wider in the "butt-dyno" area.) The Suzuka is an FIA-approved fixed-back racing seat but uses advanced materials for driver comfort and style. It is also designed for use with a six-point harness. We chose a fixed-back seat since there is no backseat and no need to tilt the seat back forward. It's also smaller and lighter.
The pedal set comes from Wilwood (as do the master cylinders and brakes), though our unique firewall and the need for adjustable pedals means we have to modify their setup somewhat. Only Wilwood has all the various pedal sets and balance bars we needed to get adjustable pedals with perfect ergonomics and their track-proven performance. A balance-bar setup is heavily used for circle track racing because it allows different master cylinders to be used on front and rear brakes with adjustment of the relative pressures between them at each position of the brake pedal. It's a great option for use on the street for the same reason: optimum tuning of master cylinder and caliper piston diameters for each end of the car.
The steering column is from ididit, with a tilt column. The most important part of the steering is the hands part: a 13-inch suede MOMO steering wheel tied to the ididit column with an NRG quick-release setup. On the other end of the column are Borgeson stainless steel U-joints and steering shaft that connect to the Tony Woodward rack.

Fabrication Sequence

The DSE dash insert defines the side-to-side location of the steering column, and the first thing to do was see if the Cobra seat would line up well with the column. On the other end, we had to make sure the column would connect to the rack. When the car was at Coast getting its cage, Tim Christ told me that I should roll the rack servo up so that it pointed over the motor mount, rather than under. Doing that meant that I only needed two U-joints instead of four as I had originally planned.
With the column roughly placed and the seat position generally worked out, it was time to tackle the pedals. I used Wilwood's forward-mount pedal kit and took the pedals out of the frame. From there, I added one of their balance-bar setups where the brake pedal used to be. I mounted the pedal frame to the firewall and hung the masters and connected the balance bar. With everything roughly in place, it's time to make all the parts, brackets, and hardware to keep it there but still allow adjustment. Check out how we did all that in the photos that follow.
Most of the time our stories read as if we progress from point to point and never make a mistake. That's not the case. The truth is we make mistakes as often as the next guy; it's just that we don't have to write about them.
These errors can be about not knowing enough to know better, like the floor area you can see in this month's article. Once the headers and exhaust was complete through there, it was obvious we could move the floor, and a few quick minutes sizing up the pedal situation from a prototype seat fit was all it took to get the cutting tools out.
However, there's another almost major error lurking in this story. Compare the seat bracket in the photo above with the final seat bracket photos in the main story. See the difference? The rear bracket was moved back, and it now bolts to the seat tube and not to the rollcage sill tube.
The reason for that change is that I consulted with Joe Marko of HMS Motorsports before making my final welds. Joe is a NASCAR safety consultant who works with the various teams to help them build safe seat mounts and even more importantly, safe harness mounts. Joe took one look at my "hey, look at what I did" photo and immediately took issue with it. He pointed out that the lap belt would have to ride over the top of the rear seat bracket. Belts should never cross over a non-smooth surface because that can lead to small tears that lead to major catastrophes at high speed.
Joe had another problem with my original seat brackets: He pointed out that my original design seemed oriented to supporting the driver's weight. He went on to say that supporting the driver's weight is the easy part--the hard part is keeping the seat in place during a severe accident when the vehicle, seat, and driver experience 12g forces. That usually occurs in a horizontal plane to the driver's weight at rest and is why the rear seat bracket is now oriented to have its most strength in the case of frontal collision, and why all the other seat brackets have a gusset for improved strength. --John Parsons



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