Seat Belts

The Complete Kit includes Simpson 5-point H-style seat belts. Two points are attached in the rear with the belts passing through a cutout in the rear cockpit wall. Another two points are attached on either side of the seat, and the last point, the fifth, is a thinner belt attached to the floor in front of the seat, often referred to as a crotch or anti-submarine strap.

The purpose of the anti-submarine design is to keep the entire seat harness from rising up on the torso in the event of an impact. In a front impact, the body is pushed forward, transferring energy to the rear shoulder straps that, in turn, pulls up on the lap belt.

Without the anti-submarine restraint, the lap belt would tend to crush the torso just under the rib cage where many vital organs are vulnerable. The anti-submarine keeps the lap belt down in position over the pelvis area which can withstand the g-force of impact.

It is dangerous to use the 5-point Simpson system without the anti-submarine strap.

The federal Department of Transportation (DOT) requires that all DOT legal seat belts have push button release. The Simpson harness, without a push button, is therefore not strictly legal which may be an issue in some states. However, properly installed, it is safe and provides good protection.

Note that the Breeze seat is only held in place by four bolts. This is not a safety issue because the seat belt restraint system is designed to work independently of the seat itself.

Seat belts are only one part of the Roadster's safety design. The chassis, with its brace structure, the “breakaway” mounting of the rear fuel tank, the roll bars, and the collapsing steering wheel are all part of a protective system.

Anti-submarine belt centered on seat and 14" back from 2x2 square tubing

Some FFR builders assume that the fifth strap is for racing applications only, and not necessary for a street legal vehicle. In fact, it is safer to only use the lap belts if the anti-submarine strap is not installed or fastened.

INSTALL THE ANTI-SUBMARINE STRAP TO MAINTAIN THE INTEGRITY OF THE SIMPSON HARNESS DESIGN.

For racing applications, the anti-submarine strap should be attached to a welded vertical ring aligned with the chin-to-pelvis line of the driver. The optimal racing configuration is a through-the-seat strap design.

However, for street applications like this build, a less robust method may be used.

Center the strap using the seat cushion as a guide, and drill a hole for the attachment bolt that is 14” back from the edge of the 2×2 square chassis tubing that frames the front floor of the cockpit.

This hole should pass through the seat plate of the chassis. Do not attach the strap only to the aluminum floor panel.

This mount location is roughly in line with the imaginary line from chin to pelvis as recommended by Simpson (see Simpson seating positions).

Position the bezel over the rear wall cutout and drill holes for screws

Drill screws holes for the four seat belt bezels. For the final installation, cut rubber gaskets to fit the bezels with a horizontal slit in them (for the belts to pass through) and position the rubber between the rear cockpit wall and bezel. This will further close the cutout gap and keep moisture out of the trunk area.

After the seat belt is passed through the bezel, attach to the tabs in the upper trunk with the provided hardware.

Roll up the excess strap lengths; hold together with a small office supply metal clip to conveniently store out of the way.

Preliminary seat belt installation with bezels; note submarine strap

Temporarily roll up the excess seat belt webbing and clip it to store out of the way; final assembly is completed after carpet is installed