Harness (Lap Belt) Mounting

[DesertGuy1]

Looking at the BITD rulebook, I had a couple questions regarding mounting of the harness, lapbelt specifically. I have seen where people simply cut off the shank of the eyebolt and weld it to a nearby tube... is this acceptable, per being "tech'd"? Also, can the eyebolt be located on a tab that is welded to the primary structure tube as long as the tab is the same thickness as the tube nearby, at a minimum? Basically, can someone weld a tab onto their chassis, cut off the shank of the eyebolt and weld it to the tab and still be "legal"?

From the BITD rulebook:


The five-point harness must be mounted to the main structure members of the same size and dimension as the roll cage and be gusseted. The structure members must be in the following locations. Anti-submarine belt to the floor structure as close to the front of the seat as practical in order to exert maximum restraint to the upward movement of the seat belt and shoulder straps. Shoulder straps must be mounted behind the occupants seats and be located a minimum of 4 inches below the top of the occupants shoulders. Seat belt should be mounted a minimum of 2.5 inches forward of the intersection of the back of the seat and the sitting portion of the seat. All adjustment buckles must be a minimum distance of 1.5 inches from the seat to prevent loosening or chafing.

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[DP Racing]

I ran into this issue when I was installing a cage in my buddies Toyota. The fastest not the best application I could come up with on the lap belts was just that. Weld the eyebolt to the rocker bar 1.75X.120 DOM after removing the threaded shaft. However, after being in an instantanious 50mph lateral flip I'm changing it to what I would've done given the time. Double shear application tabs .125" each and NAS bolt for the clip, I'm sure a grade 8 would suffice. The rest of the mounts were able to wrap around the tubing which wouldn't be bad for the lap belts if they were longer. The mounts I installed didnt fail but reading about "G" forces and experiencing them are two different things. I did remove the galvanizing on the eyebolts and the millscale from the tubing before I welded them which helps but... there is always a better way.

[Zambo]

So in other words you would put two tabs with a bolt going between them and clip the harness to the bolt?

[DP Racing]

That pretty much sums it up. The distance between the tabs would be the thickness of the clip on the belt + 1/16th". I guess you could add gussets too. I'm about to start on a class 8 for myself so my brain is all over the place with different fab options.

[loufish]

Here's another idea, if it works for you, then great...

I take heavy wall tubing, and drill/tap for 7/16"-20 threads...this threaded spacer (about .625 OD) can now be welded into the roll cage tubing after of course drill ing a hole for it.

The forged seat belt eye bolts can then be threaded into the threaded spacers. This keeps you from having to worry about eyebolt strength after cutting/welding them onto the roll bar structure...

[DesertGuy1]

After a couple conversations with Bill Savage and going through the "rulebooks", I ended up making a tab that will be welded to the primary structure, then bolt the eyebolt to it. The tab "locates" the eyebolt where the rulebooks say it needs to be. Im not sure how closely this is checked but figured I'd rule out any issues down the road. I do like the idea of the tapped tubing though...

[Safer1]

The proper mounting for the lap belt is 45 to 60 degrees from the centerline of the pelvis as close to the seat as possible. The lap belt should be mounted in double shear and be allowed to swivel. This allows the lap belt to follow the pelvis and increase the chances of it stay in proper location on the pelvis. I would always recommend a bolt in mount over a clip in mount for strength. When mounting to the chassis you must remember that it needs to be strong enough to take a pull of 3500lbs. This is realistic lap belt loads. Instructions from your seat belt manufacturer should have a chart with proper lap belt location.

[Zambo]

That seems like a lot of work to get to the desired end result, which is placing a hole big enough for the seatbelt clip where you need it. Rather than fabbing up some complicated tab to hold the eyelet, why not just make the hole in a regular old tab a little bigger and clip the seat belt right to the tab? In the drawing above, if you just welded a 1/4" thick tab in the same place I think you'd be fine. Add a gusset to it if you don't think it would be strong enough.

[RoosterBooster]

That seems like a lot of work to get to the desired end result, which is placing a hole big enough for the seatbelt clip where you need it. Rather than fabbing up some complicated tab to hold the eyelet, why not just make the hole in a regular old tab a little bigger and clip the seat belt right to the tab? In the drawing above, if you just welded a 1/4" thick tab in the same place I think you'd be fine. Add a gusset to it if you don't think it would be strong enough.

Zambo
im not a expert ... but here is my 2 cents anyway;

i think the (heat treated) lap belt clip opening is designed to be clipped to a ( also heat treated) eyelet that "spreads" the load into the frame (or tab in desert guy`s drawing).... in other words ; i think there would not be room for the required "extra material" to safely hold the clip with a (non heat treated) tab ?!?
... i hope this makes sense

i really like loufish and desertguy1`s ideas; they let you use the eyelet "as it is" (no cutting/welding)

[Zambo]

Is just welding a tab on like I suggested as strong as building a multilayer mount for the eyebolt? No probably not, however just because it isn't made out of heat treated, normalized, honey dipped unobtanium doesn't mean its going to break either. This isn't a tab that's holding on a trophy truck A arm. There is a big difference between strong as possible and strong enough. Even in a 15 G crash, a 200 pound guy is going to exert a 3000lb momentary force spread over the two lap belt mounts and the shoulder and crotch strap mounts. Each tab would see at the most a 1000lb momentary hit. I think a 1/4" thick tab, which is bigger than what a lot of guys use to mount large shocks, would hold up fine.