Thread: Seat & Seat Belt Mounts

Tweet

A short clarification. I mounted each seat with four of the plates I described. The seat belts are anchored with two more for each belt. I did not mount the seat belts to the seat. They are mounted to the floor also, at the proper distance behind the seats as recommended by Juliano.

Jack,
Thanks for taking time to answer. I had typed out a reply to your first part, but must have failed to hit "submit" after previewing it. I had stated that the only thing I might do differently was to perhaps extend the four rear seat mounting plates back to pick up the seat belt mounting points, per Juliano's spacing in an attempt to increase the continuity of the seat/belt mounting system. I will look closer at that, but you and I are on the same page relative to the separation aspect - take reasonable steps to keep the body attached, but if they do separate stay with the body, and don't ever become the cotter pin connecting the two via the seat belt. Since the upper shoulder harness point is a body mount, the choice is made for me.

Kitz,
Inertia is absolutely the key to this discussion, and if you have concern with your moment of inertia pulling through your mounting system then I would say that you need to beef up your under floor plates. I believe that it is impossible to prevent differential movement between body and frame in a severe crash, and I choose to tie my butt to the body, not to the frame.

Originally Posted by rspears

Jack,
Since the upper shoulder harness point is a body mount, the choice is made for me.

Are you planning to mount the shoulder harness to the floor? I might be misunderstanding. The harness mounting point should be up by the shoulder (see how factory shoulder belts are mounted). If the mounting point is low a forward crash could compress your spine, as tech mentioned early in the thread.

Originally Posted by pro70z28

Are you planning to mount the shoulder harness to the floor? I might be misunderstanding. The harness mounting point should be up by the shoulder (see how factory shoulder belts are mounted). If the mounting point is low a forward crash could compress your spine, as tech mentioned early in the thread.

Yes, my shoulder harness mount will be anchored to the 1x1 tube frame just above the belt line, at the top door hinge point. This makes it a body mount, which then drives all other seat and seat belt points to be body mounts, too. The only safe way, in my opinion, to mount to the frame is if you build a total frame mounted cage assembly, including floor pans, that the body fits over. If I had such a cage system my choice would be to stay with the frame and allow the body to go its own way, like a AA Fuel Dragster. The issue, again in my opinion, is to consider the point where the body (God forbid) separates from the frame, and at that point if you have mixed your anchor points, some to the frame, some to the body, then the seat belt system is going to be the cotter pin trying to hold the body/frame together (I like that, Jack!!), and the passenger is going to get squeezed.

Originally Posted by Henry Rifle

A short clarification. I mounted each seat with four of the plates I described. The seat belts are anchored with two more for each belt. I did not mount the seat belts to the seat. They are mounted to the floor also, at the proper distance behind the seats as recommended by Juliano.

Jack,
Did you buy your reinforcing plates or just use flat stock with a bolt? The plates from Juliano are nominal 2"x4" with nut welded to the bottom side and all four sides bent down about 30 degrees, which adds a bit of strength and eliminates a cutting edge against the flooring. I like your idea of bonding them to the floor with the bolt sticking up.

I used flat stock, but rounded off the edges and the corners with a grinder. The nut welded in the center to take a bolt isn't a bad idea. I thought of that myself, but it's easier to get things lined up with the bolts set firmly in place and sticking through the carpet . . . if I had carpet, that is.

Flat stock rounded corners & edges is where I was headed, but Juliano's plates and their statements about them had me questioning the approach. My thought on the nuts welded to plates is that the threads are going to be subjected to any road spray, and especially in the winter/early spring when there are residual chemicals on the roads from the ice melt process corrosion will be a problem. Bolts sticking up puts the threads inside. Yeah, my "carpet" is going to be shiny silver foil for a while

I had the same thought about the thread on a nut getting grungy. However, you could use a Juliano's plate and run a slightly longer bolt through it to poke through the floorboard. A little spot weld on the head would keep it from turning when you take the seats out (many times).

I'm not concerned about using the plates. The way mine are glassed in, I see no way that they are going to turn, twist, fold up, or present a sharp edge to tear through the glass. If I hit something that hard, it's all in the luck of the draw anyhow.

I think I will use Juliano's plates with the nuts for the seat belt mounts that go through the floor, as they will very likely never be coming out once bolted in place, and the bolt/nut can be painted with the bottom of the car. For the eight seat bolts I will make plates, rounding corners and edges, with grade 8 bolts tacked to the bottom and the plates bondo'd to the floor. Should be good to go, and I agree 100% on the luck of the draw comment, or put another way, "...in God's hands".

Yep, Newton's laws are not to be disregarded. The ACLU is no help there.

I'll put my 2 cents in. I built and raced stock cars for years. DO NOT MOUNT seat belts to the frame of the car. Especially in a side impact body will be moved or crushed first and then frame. Your body will not tollerate this kind of sudden compression. If belt is tight it may not take much of a side impact to result in serious internal injuries. With a race car we build a mount or cradle to hold seat and attach lap and sholder, and crotch belts to that structure so as seat moves so do belts with body. No in a street car this mostly is not entirely possible. With a fiberglass floor, or for that matter a steel floor, that doesnt have the well and areas to crush, best bet would make a frame or sufficient reinforcement plates under floor and attach both the seat and belt to that structure. So in the event of a crash that would move this area around the seat and belts would move as a single unit, keeping driver or passenger attached in seat. With a single shoulder belt the body with a reinforcement plate should be sufficient. Now this is not the safest way to do this, but without a cage type structure, basically creating a pod, if you will, for the driver that will move as a single unit belts, seat, and driver. I'm not sure if I described this well enough to picture it, hopefully you get the idea. If you are after safty, consider this. I would look at race car seat mounting and design and try to incorporate as well as you can into your seat and belt design. Especially with a fiberglass car you just don't have alot to absorb that energy in the event of a crash. Of course I understand that most of our cars are unsafe in this reguard, compared with todays crash standards. But unless you are just after making it leagal, put some thought into if this happens, what will hapen to the seat in relation to the belts. Attaching to the frame, unless the seat is attached at the same point on the frame, is just making an anchor to keep the body, (yours) in place until the coronor arrives.

I sure wish that I had been "smart" enough to have taken pictures of my seat belt attaching assembly - the one that spreads the load through the entire floor as noted in the post above.

Dlotraf33, I believe what you are describing is what I tried to summarize in post 19 above. I agree with you that it is not safe to mix the mounting points on belts & seats, and for my car, built the way it is, the right approach for me is to mount everything to the body, and then to reinforce the body to frame mounts to try to minimize the possibility of the body and frame seperating in a crash.

Yes that sounds like the right approach. Unless you have very poor mounts on body to frame the body is not going to completly seperate from frame, unless it is a very bad accident. Lets hope that never occurs. I may have been a little over zealous in stating the point. I have seen guys bring cars to the track with belts bolted to the floor, and tech officials let it slide. And in a stock car you know you will get hit, sooner or later. So if I was, I surly didn't mean to be. I think with a fiberglass floor I probably would some sort of reinforcements, either plate, maybe 4 to 6 inches wide that extend from front to back of seat mounting points or some box type material, as room and your taste dictates. And this is probably redundant, I appoligise, use grade 8 hardware to mount seat and belts. If you use box under seat I wouldnt use a light gauge though, .120 min. wall and if thru tube of course use a welded in bushing thru tube. It sounds like you have a pretty good grasp of the principal. So nuf said.