Seat belts harness mounting

[NectarNick]

I intend on installing some schroth 4 point rallye harnesses. I have the harness roll bar from FFR. How are people mounting the lower points that go around your waist?

Thanks,
Nick

[Hindsight]

The right way to do it is to weld-on harness mounting tabs that allow the mounting point to swivel, onto the frame.

https://www.summitracing.com/parts/a...nHQRoCuuPw_wcB

[phil1734]

Unless you're a professional welder and plan to run regular NDT tests on your chassis, I'd strongly discourage the use of weld in brackets for seat belts.

The best solution is a high quality eyebolt such as here: http://teamtechmotorsports.com/shop/...d-lock-washer/, but as you'll never find one long enough to reach through the 2" box that makes up the FFR frame your next best bet is these: http://teamtechmotorsports.com/shop/...lt-in-bracket/ with an OEM swivel and a 7/16-20 bolt through the whole thing. Both allow for a bit more movement than Hindsight's solution, don't need specialized equipment to install or maintain, and will transfer load properly in case they are ever needed (Sorry - I don't see any easy, reasonable way to get that bracket in the correct orientation for a lap belt.)

(Source optional of course, I've just always used Teamtech for my safety gear.)

[Hindsight]

The eye bolts will work too. I don't know how safe it is to just bolt them through square steel tubes though, since the tubes can collapse. Not only that but your eye bolt and nut are going to hang down below the under-surface of the car; they can hit things and become damaged. If using the eye bolts, I would probably weld some 3/16" or 1/4" plate in between (and on top of) two of the frame tubes and then bolt this through that steel plate. But that gets you back to welding again. As for NDT testing, if you are bolting the mounting eye bolts to a frame that is welded together without NDT testing, isn't that the same thing as a bracket that is welded to the frame without NDT testing?

The biggest issue IMHO in installing the harness mounts on the 818 is getting the angles right for the belt. The lap belt is supposed to have a very specific angle toward the rear. There is a range, but given the seat mounting position, you don't get a lot of flexibility in the position of the eye bolt. For a given seat in a given mounting position, there is going to be one spot where the bolts should be and the range is going to be like +- an inch. Chances of that being right on a big steel tube are very low. That's why I took the approach I did of welding them to thick, wide, solid bar stock that is then welded between two frame tubes. If you look at the FFR shoulder belt mount, they took the same approach.

Here is my mount:

[phil1734]

The eye bolts will work too. I don't know how safe it is to just bolt them through square steel tubes though, since the tubes can collapse. Not only that but your eye bolt and nut are going to hang down below the under-surface of the car; they can hit things and become damaged.

The eyebolts (or regular bolts in case of the bent brackets) would go through the tube horizontally so they don't stick down at all. I'm not aware of any sanctioning body that doesn't encourage this method, and on any carbon fiber or aluminum chassis it's virtually required as welding to them can be incredibly difficult.

As for NDT testing, if you are bolting the mounting eye bolts to a frame that is welded together without NDT testing, isn't that the same thing as a bracket that is welded to the frame without NDT testing?

Not really, as you won't be applying the load directly to the weld. Yes, on these cars it will all lead back to a welded node eventually, but that load is considerably more spread out by the time it gets there. If anyone is seriously racing a tube frame car they should be doing NDT checks every few years if for no other reason than chassis compliance.

I would question that your brackets, while probably okay, meet the minimum cross-sectional area for wheel to wheel racing applications.




In any regards, just don't be the guy that attached his lap belts through the transmission tunnel using a riv-nut. That one still gives me nightmares.

[Canadian818]

I suspect FFR does some form of testing on their welders to ensure they're making quality welds. Not every pretty weld is a good weld, and not everyone who "can" weld "should" weld things like belt mounts, roll cages, etc, without some kind of formal training.

[phil1734]

Not every pretty weld is a good weld,

Even if it gets a lot of likes and shares on facebook?

I wish more people realized this.

If it looks like absolute garbage it probably is. Anything else is just an educated guess.

There's a old saying in the aerospace world that welds are just cracks waiting to open up at the most inopportune time.

But I digress.

[flynntuna]

Question, if you're using an eye bolt thru the frame tube, shouldn't you be using an Anti-crush tube to put the eye bolt thru to keep the frame from crushing when torqued down or torn in the event of an accident?

[phil1734]

In a perfect world yes. Typically they are either threaded into a bushing or thru-bolted with the giant supplied fender washers to prevent crushing/tear through.

With that said, I've still never seen one long enough to pass thru the main frame members of an 818 (you've need around 2.5" of thread IIRC, most are ~1.875" max.)

[NectarNick]

If you use the regular bolts with bent brackets or eye bolts what tubes do you go through? One side is pretty easy through the side of the car but on the other side do you go through the "transmission tunnel" looking support where all the wiring goes? Does anyone have pictures or other examples of what they did? Thanks so much for the help.

[phil1734]

That's one of the great questions of the 818 chassis design.

I understand not having exact locations as every seat, driver, and installation will be slightly different, but not having anything safe to anchor through there is borderline negligent and sloppy design in my book.

You DO NOT want to go through the trans tunnel bars unless you've somehow triangulated them back into the chassis, which would be incredibly difficult to do with the fuel tank in it's stock location.

edit: The "lower" trans tunnel bar might be okay in between the X-bars for the seat (I'm not in front of a chassis to F-Me-A it right now). The top and vertical bars are bad news bears.

[turbomacncheese]

I thought the 818 chassis design anticipated reuse of the donor seat-belts. Maybe they could have anticipated the desire for harnesses, but I wouldn't come down on them too hard. Then again, I'm not installing harnesses....