Please Be Seated: How to Mount a Seat

A seat is a seat until it comes loose in a crash. Even with all thebelts securely latched, the driver is almost free to move about thecockpit when a seat mounting comes loose. Often he is bounced aroundlike a pinball.

Worse yet is a case in which the seat is mounted to the floor but thebelts are mounted to the cage. In a hard side impact, the cage can beshoved over toward the right side of the car. The seat is then, no punintended, 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 aredoing their best to deform the seat.

At no time is a poorly designed seat mount a healthy situation. I'm surethere are some racers who can tell a tale about mounting seats to thefloor and having survived tremendous impacts. These stories areanalogous to those stories of drivers with no seatbelts being thrownclear of an accident.

I have seen a variety of seat mountings over the years, even inprofessionally built cars in which the seat mounting looked trick andsaved a pound or two of left weight. Some use one mount at the top ofthe seat and another near the junction of the seatback to the seatbottom. This cantilevers the front part of the seat out into space.Looking trick and saving a little left weight can be a foolish way tobuild a car. I think builders wanting to save a little time do thissometimes.

The method we will describe here for mounting a seat is not the only wayit can be done. However, this way is tried, true, and strong.

Rollcage Dummy

For this project, we again used Stock Car Racing's rollcage dummy. Thisis a generic cage built of lightweight exhaust pipe material to make iteasy to move about the shop. Much of it is tack welded together tofacilitate taking parts off and on as well as changing itsconfiguration. With this dummy, only components necessary for theproject are in place. There are no extraneous pieces to distract the eyein a photo. The dummy can be tipped to any angle necessary for a photothat 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.

Mount Up

Having used a variety of seat mountings over the years, I like a mountthat attaches only to the rollcage. The mount should cradle the seat andbe strong enough to carry seatbelt mountings. Seatbelts should beattached directly to the seat mount so that if the mount/cage moves in acrash, you won't be strangled by belts attached somewhere else.

We used a CSC Racing seat mount kit for this project. This kit embodiesall the features I like in seat mountings. The parts are made of11/2x0.095-inch wall tubing and are pre-bent. Most of the tubing is alsonotched. The exceptions are the parts that must be cut to length to fityour particular installation.

The instruction sheet is clear about which steps to take and in whichorder. The notched side frames are welded to the short slider tubes.Then the upper and lower crossbars are inserted, making assembly notunlike an erector set. It makes for an easier installation if only thelower cage door bar is in place at this time.

The seat side frames should be wide enough apart for the seat to cradledown between them. The front edge of the seat should rest on the frontcrossbar.

Ergonomics is a big word for making sure the driver is comfortable andwell-fitted to his surroundings in the cockpit. An ill-fitting cockpitwill be distracting to a driver. This can lead to driver stress andfatigue 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 typeand location. The steering wheel as well as other controls can then bepositioned.

We decided to use an Oval Craft seat obtained from our local supplier,Racecar Engineering. This is a nicely formed, well-crafted aluminumseat. I particularly like the transition angle of the seat bottom to theseatback. In addition, the cover has tabs to tug on while snapping itdown.

Most stock car seats have a 20 degree angle between the back and bottomwith the headrest at a lesser angle. Normal mounting will have theheadrest in the vertical position. This will set the angle to mount theseat. Block the seat up with whatever is handy to get it in the positionyou 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 alsoneed to consider the clearance between the driver's helmet and the topof the cage.

With the seat blocked up in the desired position, the side frames andupper and lower crossbars can be assembled around the seat. There shouldbe a minimum of 1/8 inch per side clearance between the seat and theside 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 goodway to hold everything in place temporarily. The notch is easiest cutwith a tube notcher, but it can be done on a chop saw or even with ahand grinder. Once this has been done, the lower crossbar can be tackwelded to the side frames.

The upper door bar can be tacked in place so that the upper crossbar canbe located. When this is done, the upper crossbar can also be tacked inplace. There is one more mounting bar, which should be located to theright side of the upper bar and then to the rollcage crossbar. With thistacked into place, the seat frame can be gently removed from thechassis.

Out on the bench, weld all joints. Weld part of a joint, and then go tothe next joint and weld part of it. Repeat this process of movingaround, partly welding joints until all is complete. This will minimizewarpage 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 with7/16-inch Grade 8 bolts. The bolt size may seem like overkill, but usinga 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. CSCsupplies tabs for mounting all of these. We used some of theirs and someparts from A&A Manufacturing. From CSC we used two tabs on the frontcrossbar to bolt to the seat. Additionally, CSC's tabs were used forside seat mounting bolts, and one tab is used for a five-point harnesson the front crossbar.

Belt Attachment

A&A has a new part, a "U" shaped piece used for belt attachments. Youshould always mount belts between two tabs, putting the belt attachmentbolt in double shear. The A&A bracket lets us weld one tab in place andstill have the attachment bolt in double shear. We used these for thelap belt holders.

For the shoulder belts, we did it two ways. If you have room, use thedouble shear bracket. If the seat is too close to the cage bar to allowthe adjuster or mounting hardware to clear the seat, then use a singletab pointing down as shown in the photos. Be careful to mount all thebelt hardware in the correct location.

We selected a six-point harness from Leaf Racewear. The lap belts shouldangle up at about a 45 degree angle from their attachment point. Theyshould follow a path across the pelvic area of the driver. The mountshould be located so that the belt does not pull against the edge of thehole where it goes through the seat. The double shear bracket here isnice to have because the belt hardware can freely pivot.

At no time should the belt adjusting hardware contact the metal seat. Itmust be on either inside, or preferably outside, the seat. Such contactcan cause improper adjustments as well as the infamous "dumping" where abelt is stacked against one side of the hardware. Dumping could causeshearing against a hardware edge.

The shoulder belts must not depend on the seat hole for their verticallocation. There should be a seat mount bar or chassis bar behind theseat that locates the height of the belts coming off the driver'sshoulders. The bar should allow belt angles of about 10 degrees downbehind 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 hasbeen in since I survived puberty. The purpose of the strap is not tokeep you from sliding forward, but to keep the lap belt from riding upand 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 doublestraps attach to the lap belt mounts. Then they wrap under the seat andgo up through the front hole in 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.

Conclusions

Take time to properly position a seat; use a mounting that attaches inthree places to the rollcage; pick a seat that fits properly; use thecorrect brackets; and finally, use care in selecting belt mountingpoints.