Best place to bolt lap belts with seat mounted to cage

I got my cage builder lined up. While thinking about what I wanted to do with the new cage, it occurred to me that I might want to change where the lap belts are bolted. In the old car I used the factory connections for the lap belts, but my seat was also mounted to the factory seat brackets in the floorboard. If I got hit hard enough from the side in the old car, the seat and lap belts would move together, independent of the cage.

Now, with the new rules allowing the seat to be mounted to the cage (or more specifically to framing attached to the cage), should I be bolting the lap belts to the cage as well?

Yes, and be sure to have proper tabs/tubes installed for 5th or 6th points. I expect 5 point belts to be gone soon with 6 being minimum so be prepared. Good luck with the build.

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Originally Posted by seckerich

Yes, and be sure to have proper tabs/tubes installed for 5th or 6th points. I expect 5 point belts to be gone soon with 6 being minimum so be prepared. Good luck with the build.

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When you say tabs or tubes for the 5th and 6th points, are you talking about tubes through the seat frame supports for thru-bolts, and tabs for bolting outside the frame supports? This may be one of those times when a picture is worth blah, blah, blah.

In the rear for the lap belts we use 1/4 thick tabs to bolt the harness in or to attack anchor eyes for snap in style. If you run a bolt through a tube it should be sleeved to prevent a break point. Just sold the last 2 cars with this setup so I will see what I have pictures of.

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Originally Posted by seckerich

If you run a bolt through a tube it should be sleeved to prevent a break point.

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That must be what the GCR means when it says "Holes in the roll cage to accommodate the installation of the harness must be bushed and welded completely."

For gaps in the GCR I always look at the FIA specifications. Frankly I trust the FIA specs a bit more as they back up most of their findings with engineering and testing. There are a few diagrams of seatbelt mounts and the rollcage bushing you mentioned. Take a look at this:

http://argent.fia.com/web/fia-public...11)-080910.pdf

Just went through this with my new tub and cage. The shop welded anchor eye-bolts to the seat frame for the lap belts and 2 sub belts for a 6-pt system. Make sure you go over how you want the belts mounted with the shop. There seem to be some differences in how belt manufacturers want you to mount the them.

Good to see you're getting to the point of a new cage. Hope to see you back at the track soon.

David

Keep in mind that (even back in 1969) Nissan and most OEM designed their seat mounting in a side impact to move to move inwards as the trans mount broke, the trans drops down, and the tunnel collapses. This give as much crush zone as possible in a side impact. Later cars have structures called "pusher blocks" that physically move the seat inward in a side impact.

I would be reluctant to mount the seats directly to the cage for fear of too much impact force being transmitted directly into the seat.

FYI... in the 240Z's case, look at the scallops in the front set mount and how the rear seat mounts are two separate pads separated by just the pan. Also, look at the trans mount in 1972 and later 240Zs. I've seen 240Zs hit the in sides where the seat moved 10" inward delaying the load imparted to the driver.

I like John's comment and always keep the following in mind--OEM mounting points for belts should be pretty darn good. There is lots of engineering in them.

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Originally Posted by joeg

I like John's comment and always keep the following in mind--OEM mounting points for belts should be pretty darn good. There is lots of engineering in them.

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Good point. A lot more engineering than I can afford to buy, for sure.

Steve can probably speak better to this than I can, but street cars don't have a cage. In a race car, the cage is what protects you.

Your shoulder belts are attached to the cage. If you attach the seat (and belts) to the floor then it's possible for the seat to move independent of the cage, which seems bad to me given the shoulder belts are always attached to the cage. Attaching the seat to a frame that is attached to the cage keeps the seat in position with the cage and allows everything to move together.

David