Double bar harness strap installation

[Terry Oxandale]

Looking for some help from the forum on a question I have about the "double bar" method of attaching a belt to the floor. Because I basically sit on the floor of this project, I've chosen to use this method (perhaps used by the open wheelers?).

Anyway, the question I have is should the bars have any solid spacers (washers for example) between each of the bars, or is the entire assembly tightened such that the bars squeeze the belt material? The wrapping method self tightens, so I'm not worried about the belt sliding out of the assembly, but I am worried about the pressure the two bars place on the belt webbing when I tighten the bolts, and concerned that it may 1) damage the belt from being squeezed to tightly, or 2) the webbing (because it is not a solid stiff material) will allow the assembly to loosen over time. I realize that if a solid spacer is used to limit the amount of pressure the bars place on the webbing, it would have to be a very accurate dimension (too thick, and the belt is not adequately secure, too thin, and I'm back in the same place that prompted this query.

The belts are about .060" thick, so doubling that on the bottom layer makes for a less than ideal "solid" assembly, even with the bolts torqued and perhaps locktite added to them. It just doesn't make sense to not have spacers between the bars, and having those spacers just slightly thinner than the belt material (e.g. .050" to .040"?).

 

[Randy V]

Terry,

Thanks for asking before doing...
I used to be an SCCA Tech Inspector and I have to say that I would have failed any car's restraints that were anchored in the manner you are proposing. The metal bars provide a concentrated stress point and could easily cause the harness to tear.
Instead, take a look at a round bar or at the very least a SFI Certified single point mount.
If you go to page 92 in the link here, you will see a few different suggested mount styles.

http://scca.cdn.racersites.com/prod/assets/2015 GCR February.pdf

I will look for more examples and update...

--- edit ---
Was looking for FIA spec and IMSA. IMSA just says that the mount must be able to withstand 25Gs.. FIA Spec has been elusive. BUT. My favorite racing store has the mounts that may work for you:
https://www.pegasusautoracing.com/group.asp?GroupID=HARNHARD

Look at the bent bolt in plate:
https://www.pegasusautoracing.com/productselection.asp?Product=2388

Remember that the belt must have the edges turned in as shown on the SCCA drawing figure 5...

 

[Terry Oxandale]

Thanks for responding Randy. My lap and shoulder harness are well mounted using floor mounts or bars situated specifically for the belts. My problem stems from the anti-submarine belts. I wanted to attach them to the frame next to the lap mount points, but the seat prevents my sitting on them (without rubbing or placing an undesired angle on them) as they pass down the crotch area , and then under each leg (much like a parachute harness). So the last option I had was the double bar. The reason I dislike the other options is that the forces are not aligned with the mounting method. The double bar is aligned so that the entire width of the belt is stressed evenly (on forward body movement on impact), and the bars have been rounded to again, reduce point stresses.

Thanks again. I'll go over this again to see what can be improved.

 

[Randy V]

What seat are you using Terry? Is yours a 6 point harness then?

 

[Terry Oxandale]

The seats are a fiberglass insert set into the frame. Basically a reclined seat bucket that is held in place with 16 small bolts. the "seat" portion (directly under my bum) lies directly on the floor of the chassis (which is .125" aluminum).

I'm using a 6-point with the mounting method noted above being used on the floor (with reinforcement and plates) spaced 3" apart from each other.