Seat Belt Mounts

Roger Allen · 05-02-08, 04:11 PM

Hi,

I'm figuring out the top mounts for the shoulder straps for six point harnesses. I've looked at a thread in the GTD section of the forum and the mounts described there look to be higher than horizontal which would allow vertical body movement.

European industry and FIA recommend that the shoulder straps must be between 0deg (horizontal) and 45deg (down) (see securon.co.uk). Looking at racing/rally seats they all have cut outs to accommodate these horizontal or lower strap mounts. Any advice would be appreciated.

I'm building an RCR with a full rollcage.

regards

Roger Allen

Andy Green · 05-03-08, 02:43 AM

Hi Roger
If you're going for a full roll cage, why not get a horizontal bar added to the main rear hoop to take the fixingss. The attached is what I've done on my Tornado chassis

Regards
Andy

Dave Bilyk · 05-03-08, 05:10 AM

Andy, great job on the roll hoop, inspires confidence.. What struck me about Rogers post was the shoulder strap angle which seems to makes sense as under extreme situations, you want the straps to keep you down on the seat. I was thinking of reinforcing or replacing my existing horizontal bar which is not man enough, so this has raised another point for me to check later today. What angle will your arrangement give?

Roger, when I sit in my seat, my shoulders are slightly higher than the back, just enough not to need cutouts, but I may need to rethink if there is any substantial upward angle..

regards
Dave

Roger Allen · 05-03-08, 06:57 AM

Hi,

Many thanks for those thoughts

I too have a horizontal bar in the RCR roll cage but a trial fit left the shoulder strap mount too high - I'm 5'10" and my wife is 5' 2" - the mount needs to be around 2" lower. Putting in another lower horizontal bar would push the seat back forward by around 2", not good. The current bar is positioned just above the seat back which slots in neatly below it. So I'm thinking of putting a strengthening horizontal channel section bar behind the bulkhead and screwing snap hook eyes into it using supplied anchor plates. There's just enough depth in the seat and padding to accommodate the hook and eye on the inside.

regards

Roger

Brett James-McCall · 05-04-08, 05:03 AM

Roger,
If you are going to put it on the road, please don't forget that SVA requires a minimum height. I'll need to look it up.

Brett

Howard Jones · 05-04-08, 01:54 PM

You should read the mounting instructions for the belts that you intend to install. I am however certain that a downward angle of 45degrees will be VERY dangerious. As the body moves forward in a shunt the shoulder belts must hold you in place and assorb energy without imparting vertical force into your spine. The only way this will work is if the belts pull you straight back or very nearly so. If the top mounts are more than a couple of inches below the top of you shoulders when seated then the forces will COMPRESS YOUR SPINE!!!!! This is very bad.

I believe that the belts I have, wanted no more than 5 down and 10 degrees up from horzontal as measured from the top of the point that they contact your body when fully tightened for this reason.

The belts are not there only to keep you in the car but to absorb the forces that are present in a heavy shunt and not to transmit them to your body in ways that will dammage you.

The lap belts also have recommeded mounting instructions. But basically they should pull you slightly downward at the point where you hip joints are attached to you pelvis. They CANNOT ride up in a shunt. If they do your internals will be subjected to severe tramma. This is the main reason for a sub belt. To hold the lap belt in place and prevent you from being forced downward thru the lapbelt.

My seat is in a layed back possition of aprox. 33 degrees as are most GT40 seats. In this VERY laid back seating possition you can see how easy you can be thrown forward and slide downward into the footwell at the same time.

The idea is to hold you pelvis in possition with the three or four lap/crotch belts and allow the upper two belt to absorb the forward motion of your upper body without compressing the spine. Any other way will HURT!!!!

The only thing left is your head and neck. This is where a HANES (sp?) device comes in. It will prevent the weight of the head and helmet when thrown forward from applying too much
force to the spine at the base of the head by restricting forward motion of the head.