Seatbelt anchor points

[TheArf]

Hi Guys just a quick question, is there any reason why when you fit the seatbelt anchor points they have to be in the vertical plain. I went to Loton Park hill climb at the weekend and I noticed that a lot of the competitors have them fitted horizontally, thus making the harness lie in the same orientation as the anchors and pulling in a straight line.
So my plan is to make stepped anchor points fitted through the actual cross member of the rollbar with a shoulder on them and fit them in from the rear of the car before welding and them in solid.

[jps]

Hi Guys just a quick question, is there any reason why when you fit the seatbelt anchor points they have to be in the vertical plain. I went to Loton Park hill climb at the weekend and I noticed that a lot of the competitors have them fitted horizontally, thus making the harness lie in the same orientation as the anchors and pulling in a straight line.
So my plan is to make stepped anchor points fitted through the actual cross member of the rollbar with a shoulder on them and fit them in from the rear of the car before welding and them in solid.

I'd need to see a picture to understand what you mean!

Do you mean the lower mounts (lap belt) or the upper mounts (shoulder belts)?

[TheArf]

Shoulder height hence reference to the rollbar cross member

Arfon

[Stot]

I think you need to look at it from the point of a frontal impact of the kind you get on the road rather than how they lay when unstressed. The belts are going to be stressed in a forward motion and its at that time you want the bolts be acting in shear, hence being vertical.

Cheers
Stot

[TheArf]

The ones that I saw at the weekend where fitted to a westfield that was entered into the hill climbing

the arf

[jps]

Shoulder height hence reference to the rollbar cross member

Arfon
the bit that confused me was the ' belts in the same orientation as the anchor', surely they are with the book setup...?

I get Stots point but wonder if it makes any difference, either way in the event of an impact the force is basically trying to rip the head off the securing bolt / tear the belt anchor plate / etc?

[TheArf]

Wish I knew how to draw pictures on here, right the standard way to insert the bushes through the cross member is to insert them from the top and then weld them in, this then has the harness coming off them at a 90 deg. angle. Are you with me so far, now instead of inserting them in the standard orientation, drill the holes 90 deg's to the standard orientation so that they run front to back and then insert the anchor bushes ready for welding.
I hope this makes what I am trying to describe clearer

Arfon

[Stot]

You mean like the attached looking from the front.

I'm pretty sure seat belt bolts are designed to work in shear. If you think about it the threaded insert is likely mild steel in most cases. I would have thought the threads will strip out of them in tension long before the graded bolt would have snapped in shear.

Cheers
Stot

[voucht]

I think it depends on what kind of harness' attach point you chose.

"Clip" ones (snap hook fixing) are to be used with eye-bolts, so Arfon, your set up is OK if it the ones you will use.

1697

1698

"Plate" ones need to be attached 90° from the belt force because of the bolt. I also I think that snap hooks (mostly used in racing cars) are not allowed on road cars, because you can easily remove them, so I reckon that's the reason why they designed the attach points it this way in the book: they expect you to use the "plate" type. But I don't know what is allowed and what is not in the UK.

1695

1696

But if I'm not mistaken about that, the only option for you is the "plate" type, and I think it makes more sense to fit them like in the book, rather than 90° from this position like you want to do (force would apply on the end of the plate instead of on the fixing point because these two points are not lined-up if you mount them as you want).

The harnesses fitted the way you describe at the hill climb race, should have been of the snap hook type I think. No?

Perhaps you can check on the IVA manual if there is anything about the allowed type of attach points.

[Stot]

Even with clip ins and the eye bolts, they are still supposed to work in shear, pulling against the axis rather than with it.

The only reason I can see to mount them horizontally is for the aesthetics of having a seat belt hang nicely when not in use but that wouldn't be a good reason for me considering its purpose.

Cheers
Stot

[jps]

Wish I knew how to draw pictures on here, right the standard way to insert the bushes through the cross member is to insert them from the top and then weld them in, this then has the harness coming off them at a 90 deg. angle. Are you with me so far, now instead of inserting them in the standard orientation, drill the holes 90 deg's to the standard orientation so that they run front to back and then insert the anchor bushes ready for welding.
I hope this makes what I am trying to describe clearer

Arfon

right. gotcha. makes perfect sense. I did wonder like what Stot said, ie the threads might strip but 7/16 is fairly coarse so I do wonder whether that'd be an issue.

Sylvain, my dad tells me clip in belts are usually for things like rally car applications, where it is sometimes necessary to get into the back, e.g. to get the spare wheel out, but the belts get in the way, because they secure onto the roll cage or in the rear bulkhead somewhere... no idea if they are iva ok or not.

Arfon, I can see how your solution would work with clip in belts, still think it wouldn't look as good with the non clip type...

[TheArf]

I see what people say and all of the points are quite valid, it's nice to throw something out there and use the knowledge that is on here, ah well back to the drawing board

Arfon

[snapper]

The threads are 1mm or less deep and don't touch everywhere so in an accident if one thread lets go the rest will follow as force multiples
In an accident you can hit many G's and that equates to many tonnes of load.