Thread: Seat & Seat Belt Mounts

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Seat belts and seats need to be anchored together. A seat belt to the frame and a seat to the floor do not move together in a crash. As the floor and seat pull away the belt gets short (owch) Frames do not always bend in the same direction as the body.

It seems we have some differences in approach regarding seat and seat belt mounting. The NSRA May 2010 Street Scene Safety First column on page 156 (thanks, Mike52) includes an article on seat belt safety by Charley Bryson who is on their Southern Illinois Safety Team, and they stress that seat belts should never be mounted to the frame (assuming that the seats are mounted to the body) due to the potential for body & frame to separate, or as 53 Willy’s points out, frames and bodies don’t always bend the same way. They also call out specifics of mounting, using 2”x4”x ¼” plates beneath the floor pan, which happens to be exactly what Juliano’s provides with their belts.
After a lot of thought I believe that 53 Willy’s hit upon the most critical point – Seat belts and seats need to be anchored together. I also believe Kitz is right – most street builds are built for moderate crash safety. Race rules only apply if you have all the race goodies, like roll cages, etc. Tech, your “engineer the whole system” takes me down this path – tying it all into a package that stays together, which I’m not sure can be guaranteed for a “normal” build. Considering a typical three point mount the retractor and center belt end will be anchored to the floor, and the upper pivot will be mounted at or above the belt line which makes it a body mount – no other option. With that in mind, I believe the key drivers are:

1) Both seats and seat belts need to be anchored together, all to a common structure. Differential movement between anchor points can kill a driver or passenger that may have otherwise survived a crash.
2) For a street car without an integral roll bar system, since the shoulder harness pivot cannot be a frame mount, then all seat and seat belt mounting points should be body mounts to account for potential differential movement of body & frame in a crash.
3) Seat mounts and the two lower seat belt mounts need substantial under floor reinforcement to prevent pull through to the extent possible. Reinforcement plates that tie two or more mounts together over a wider area are a plus, especially for a glass bodied car.
4) For a glass bodied car body to frame mounts, reinforcement plates above the floor should be significant. Use of 2”W x ¼” thick plates tying two or more body mount bolts together may help keep body and frame together in a crash.

I have not yet finalized my approach and I know this may be an emotional subject, but I welcome comments on my key points above, pro or con. I really don’t want to become a statistic due to something that can be avoided by doing things different.