Having used a variety of seat mountings over the years, I like a mount that attaches only to the rollcage. The mount should cradle the seat and be strong enough to carry seatbelt mountings. Seatbelts should be attached directly to the seat mount so that if the mount/cage moves in a crash, you won't be strangled by belts attached somewhere else.
We used a CSC Racing seat mount kit for this project. This kit embodies all the features I like in seat mountings. The parts are made of 11/2x0.095-inch wall tubing and are pre-bent. Most of the tubing is also notched. The exceptions are the parts that must be cut to length to fit your particular installation.
The instruction sheet is clear about which steps to take and in which order. The notched side frames are welded to the short slider tubes. Then the upper and lower crossbars are inserted, making assembly not unlike an erector set. It makes for an easier installation if only the lower cage door bar is in place at this time.
The seat side frames should be wide enough apart for the seat to cradle down between them. The front edge of the seat should rest on the front crossbar.
Ergonomics is a big word for making sure the driver is comfortable and well-fitted to his surroundings in the cockpit. An ill-fitting cockpit will be distracting to a driver. This can lead to driver stress and fatigue near the end of a race when he or she really needs to be alert. Take the time to fit the driver to the car. This begins with seat type and location. The steering wheel as well as other controls can then be positioned.
We decided to use an Oval Craft seat obtained from our local supplier, Racecar Engineering. This is a nicely formed, well-crafted aluminum seat. I particularly like the transition angle of the seat bottom to the seatback. In addition, the cover has tabs to tug on while snapping it down.
Most stock car seats have a 20 degree angle between the back and bottom with the headrest at a lesser angle. Normal mounting will have the headrest in the vertical position. This will set the angle to mount the seat. Block the seat up with whatever is handy to get it in the position you want it. This may take some time, but it is well worth the trouble. Get the seat angle, height, and fore-and-aft location correct. You also need to consider the clearance between the driver's helmet and the top of the cage.
With the seat blocked up in the desired position, the side frames and upper and lower crossbars can be assembled around the seat. There should be a minimum of 1/8 inch per side clearance between the seat and the side frames. The front of the seat should rest on the front crossbar. Now the front crossbar's bent end can be located to the bottom door bar. Twist it as necessary to get the right position. Vise Grips are a good way to hold everything in place temporarily. The notch is easiest cut with a tube notcher, but it can be done on a chop saw or even with a hand grinder. Once this has been done, the lower crossbar can be tack welded to the side frames.
When welding the short slider...
When welding the short slider tubes to the side rails, don't weld wherethe welder is pointed in this picture. This will cause the tube to warpas shown. Tack weld a spot 90 degrees around the tube where the notched saddle does not contact the slider tube.Now if there is any warp, it will be parallel to the crossbars, and theywill still slide easily.
The crossbars are in place...
The crossbars are in place in the side rail slider tubes. Use Vise-Gripsto hold everything in place. At this point, the sides and crossbarsshould be assembled around the seat. This can be done with the seat inthe car to be sure of the fit. The seat should cradle down between theside rails with about 1/8-inch clearance on each side.
All of the seat-frame work...
All of the seat-frame work is now tack welded. This assures that all theparts fit before final welding. A tab is placed beside the seatfor an additional mounting point. The A&A double shear tab forthe lap belt is also tacked into place. It must be positioned so thatthe belt lies across the driver's pelvic area and does not ride againstthe seat. Remove the frame from the chassis and do the finishwelding on the bench. This allows you to turn the frame for the bestwelding positions.