Seat bracket/mount advice

I have some time off the next two weeks, what better way to spend a post wedding (mine) hangover, with a welder and chop saw. I spoke with Don Taylor at NEFR this past July and he expressed some concern regarding the sliders i have in the car. "i dont trust em" . so out they come. I have a pair of OMP Extra FIA seats with bottom mount. I ordered in some brackets, i have a good amount of sheet metal removal to do before i can get the new brackets in. i need to mount the brackets as close to the floor as possible due to the halo hoop. this is what i have sketched up so far.


Am i over thinking it or should i just bolt the brackets to the floor and run it?

seems similar to the newer FIA mount:

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-KTurner
Stomp down on the exhilarator and hold on to the wheel.

Is it safer to mount the outboard side of the bracket to the sill bar of the cage to prevent body damage from attempting to move the seat?

Tim.

Here is how I did mine.

Seems fine. But if you're mounting it over the sill bar, you need to make sure you aren't sticking the seat so high that you'll be bumping your head on the roof. If I could do it again, I would have my seat mounts as low as they could go by about another inch. It's much easier to raise the seat in the bracket than it is where you can't go any lower because of the mounts. I was still able to get the mount up one slot on the seat bracket, but I can't go any more without getting into my head hitting roof bars.

But your idea is typical what most people do. Round or square tube it doesn't matter. Welding in an insert helps to prevent the tube from being crushed under load but it is not something required by RA or NASA as far as I remember. I'm rusty as I haven't read the rules since I built my car back in 2010 so you should read up on the rules.

If you're building to FIA specs, I don't see the benefit of running a round tube over a square tube. You need to add a square top to the tube and give up any sort of minor weight advantage you would have gained running a round tube.

The FIA drawing is where i got the idea however it is a bit above and beyond our skillset/timeframe. i would not be able to completly weld around a plate attached to the inner rocker panel. i will have to contact Don to see how he wants it done. any objections to building the seat bracket frame into the sill bar?
sean car looks great! makes me wish i had built mine.

The thing that makes it tough in your situation is the bottom mount seats because you'll have to leave enough room under them to get those bolts in. I know in my cars we have setups similar to that.

On the Evo I wished the bars were another 1" lower, but I guess that's what you get when there's no dash or steering wheel in the car and you're trying to figure out seat fitment.

With the BMW we put them as low as we could, even cutting out and notching the floor to provide room for tightening hardware. Looking back on it, I'd probably try to use threaded inserts on the BMW if I were to re-do anything. With the wonky floor design on the BMW, my seat tubes actually are welded to the cage along the outside edge.

Dave

For access, place the bolt heads under the bar, tack weld the heads if you like, and cut the bolts so that they are just long enough to capture the nuts and washers.

If you don't use the inserts to avoid tube crush, then use double nuts (my preference) or at least nylocks in addition to lock nuts. (The purpose of the inserts is to allow full torque on the lock nuts.)

Avoid the temptation to use tubing less than .095" wall thickness. Squaring the tubes keeps some stress off of the bolts and rails in case of that hard crash, but if you use round tube, using large hardened washers under and over the rails will relieve some of that added stress.

The threaded inserts shown in the pix above are nice!

Sean, question on your mounts.

I might be looking at the picture wrong but it looks like you are using McMaster weld nuts on the top side of the rails? Is this the case or are they actually inserts that transverse the entire tube?

Those are not MCmaster weld nuts, they are substantially meatier, Derik gets them from somewhere. They do not go all the way through the tube.

I have a case of 100 of the beefier ones. They were 0.40-0.50 cents each or so if I recall.

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Grant Hughes

So are the welds not finished in the pictures? Even if they are thicker it seems that the only thing holding your seats in the car is those small welds on the side of the nuts?

For the FIA rules geeks, my reading of the pictures above is that you need a full bobbin type tube that goes through both sides of the tube to be FIA legal?

The picture makes it look that way a bit but I don't believe that to be the case.
Pretty sure Sean's pictures are just tack welded in place, but technically the seat would be held in place by 8 little welds, not 2.

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Grant Hughes

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Andrew_Frick
So are the welds not finished in the pictures? Even if they are thicker it seems that the only thing holding your seats in the car is those small welds on the side of the nuts?

For the FIA rules geeks, my reading of the pictures above is that you need a full bobbin type tube that goes through both sides of the tube to be FIA legal?

Yeah, that's how I read it. Bushore made mine from 3/4" bar stock, drilled and threaded on the lathe then TIG welded top and bottom to the square bar.

Any reason not to use the cage as the outer support for the seat rail?

Mine:

I had the pleasure of speaking with Don Taylor a week back, class act, he was excited to hear there is another competitor on the horizon, even suggested LSPR as my first event.
We decided based on the height (OMP EXTRA) of the seats as well as the fact that they are bottom mounted, in conjunction with the brackets. my best bet to keep my head from bouncing off of the Halo hoop, would be to sure up the floor pan and sandwich plate with nuts and bolts. i realize while not the ideal scenario, i have to play the cards i have.