A seat is a seat until it comes loose in a crash. Even with all the belts securely latched, the driver is almost free to move about the cockpit when a seat mounting comes loose. Often he is bounced around like a pinball.
Worse yet is a case in which the seat is mounted to the floor but the belts are mounted to the cage. In a hard side impact, the cage can be shoved over toward the right side of the car. The seat is then, no pun intended, a sitting duck while the cage moves toward it and the driver. All this time, the driver is being yanked by the belts, and his ribs are doing their best to deform the seat.
At no time is a poorly designed seat mount a healthy situation. I'm sure there are some racers who can tell a tale about mounting seats to the floor and having survived tremendous impacts. These stories are analogous to those stories of drivers with no seatbelts being thrown clear of an accident.
I have seen a variety of seat mountings over the years, even in professionally built cars in which the seat mounting looked trick and saved a pound or two of left weight. Some use one mount at the top of the seat and another near the junction of the seatback to the seat bottom. This cantilevers the front part of the seat out into space. Looking trick and saving a little left weight can be a foolish way to build a car. I think builders wanting to save a little time do this sometimes.
The method we will describe here for mounting a seat is not the only way it can be done. However, this way is tried, true, and strong.
For this project, we again used Stock Car Racing's rollcage dummy. This is a generic cage built of lightweight exhaust pipe material to make it easy to move about the shop. Much of it is tack welded together to facilitate taking parts off and on as well as changing its configuration. With this dummy, only components necessary for the project are in place. There are no extraneous pieces to distract the eye in a photo. The dummy can be tipped to any angle necessary for a photo that is intended to demonstrate a point.
The dummy was previously used in "What Is Your Net Worth," SCR Feb '04, and I'm sure it will be used again for other projects.
The Oval Craft seat now...
The Oval Craft seat now has a Certificate of Occupancy.
The CSC Racing seat mounting...
The CSC Racing seat mounting kit with the Oval Craft seat. Some A&AManufacturing tabs are also shown. The instruction sheet in theforeground takes away any confusion about how to build it.
A Craftsman battery-powered...
A Craftsman battery-powered reciprocating saw is used to re-configurethe SCR rollcage dummy for this project. Made of exhaust tubingand tack welded together, the dummy allows us to do a projectlike this without the rest of the car in the way of the photos.
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.
The upper door bar can be tacked in place so that the upper crossbar can be located. When this is done, the upper crossbar can also be tacked in place. There is one more mounting bar, which should be located to the right side of the upper bar and then to the rollcage crossbar. With this tacked into place, the seat frame can be gently removed from the chassis.
Out on the bench, weld all joints. Weld part of a joint, and then go to the next joint and weld part of it. Repeat this process of moving around, partly welding joints until all is complete. This will minimize warpage of the unit and help to maintain its fit in the chassis.
Still on the bench, we fitted the Oval Craft seatback into the frame. All the mounting holes were drilled, and the seat was secured with 7/16-inch Grade 8 bolts. The bolt size may seem like overkill, but using a bolt this size allows the load to be spread over a larger area.
Now is the time to locate the attachment points for the belts. CSC supplies tabs for mounting all of these. We used some of theirs and some parts from A&A Manufacturing. From CSC we used two tabs on the front crossbar to bolt to the seat. Additionally, CSC's tabs were used for side seat mounting bolts, and one tab is used for a five-point harness on the front crossbar.
A&A has a new part, a "U" shaped piece used for belt attachments. You should always mount belts between two tabs, putting the belt attachment bolt in double shear. The A&A bracket lets us weld one tab in place and still have the attachment bolt in double shear. We used these for the lap belt holders.
For the shoulder belts, we did it two ways. If you have room, use the double shear bracket. If the seat is too close to the cage bar to allow the adjuster or mounting hardware to clear the seat, then use a single tab pointing down as shown in the photos. Be careful to mount all the belt hardware in the correct location.
We selected a six-point harness from Leaf Racewear. The lap belts should angle up at about a 45 degree angle from their attachment point. They should follow a path across the pelvic area of the driver. The mount should be located so that the belt does not pull against the edge of the hole where it goes through the seat. The double shear bracket here is nice to have because the belt hardware can freely pivot.
The top rear seat mount has...
The top rear seat mount has been tack welded to the seat frame. This isan A&A part. It is bent in the middle to conform to the shape ofthe seat. To the right is the upper frame-to-cage crossbar mount. It has also been tacked into place. The frame is readyfor final welding.
The seat frame is now welded...
The seat frame is now welded in place to the cage. It isattached to the cage at three locations. All of the beltattachment points are welded to the seat frame except the shoulder belts.
The seat is ready to be bolted...
The seat is ready to be bolted in. Near the front edge, the seat restson the bottom crossbar. Notice it is cradled down between the side rails.
At no time should the belt adjusting hardware contact the metal seat. It must be on either inside, or preferably outside, the seat. Such contact can cause improper adjustments as well as the infamous "dumping" where a belt is stacked against one side of the hardware. Dumping could cause shearing against a hardware edge.
The shoulder belts must not depend on the seat hole for their vertical location. There should be a seat mount bar or chassis bar behind the seat that locates the height of the belts coming off the driver's shoulders. The bar should allow belt angles of about 10 degrees down behind the seat.
Most of us are familiar with the five-point harness; it has a single, front anti-submarine strap attaching below the seat. This isn't bad. I've used one for years, and my voice is still in the same range it has been in since I survived puberty. The purpose of the strap is not to keep you from sliding forward, but to keep the lap belt from riding up and then letting you slide forward.
The six-point harness has a double strap, if this makes you feel better. The best part--it's easier to mount than a five-point setup. The double straps attach to the lap belt mounts. Then they wrap under the seat and go up through the front hole in the seat.
Take time to properly position a seat; use a mounting that attaches in three places to the rollcage; pick a seat that fits properly; use the correct brackets; and finally, use care in selecting belt mounting points.
The shoulder mounts are shown...
The shoulder mounts are shown in two ways. The best way, ifthere is room, is the double shear tab on the right. There mustbe room for the hardware without it touching the seat. In caseswhere space is not available, weld a single tab straight down off thecage crossbar. This location makes the belt pull in line with the tab.Never weld on a tab pointing straight back in this location.
This is a close-up of the...
This is a close-up of the six-point anti-submarine belt attachment. Itbolts to the outside of the lap belt mount on each side.
A bottom view of the seat...
A bottom view of the seat shows the two anti-submarine straps routedunder the seat and attached on each side at the lap beltlocation. The tab in the center is for attaching a five-point harness.This tab should point down or back, not forward or up.