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fixing 6 point harnesses


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hi guys,

i was just wondering what the common thinking was on fixing your harnesses, specifically the shoulder straps.

 

seeing as most rear cages don't come with a dedicated harness bar & my SC doesn't have rear seatbelts where do you anchor your shoulder straps to? are there any pre set fixings on the rear shelf/fire wall or do you need to be drilling dedicated fixings?

 

:)

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hi guys,

i was just wondering what the common thinking was on fixing your harnesses, specifically the shoulder straps.

 

seeing as most rear cages don't come with a dedicated harness bar & my SC doesn't have rear seatbelts where do you anchor your shoulder straps to? are there any pre set fixings on the rear shelf/fire wall or do you need to be drilling dedicated fixings?

 

:)

 

Does your car not have the provisions for rear belts though? In which case it has the holes. I am using the shoulder rear belt mount points in the parcel shelf. Not ideal due to the long belt.

 

I have seen 964RS with the belt mounted to eye bolts in the parcel shelf but you need to have a big plate under the shelf for support.

 

You can also use the rear lap belt mounts with a harness guide bar if those points are hiding under your carpet - see the Brey Krause website.

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PICT0175.jpg

 

I'm not convnced this is a good installatiion, harness bars are a good idea but but putting a bend in the seat belts is not so good.

 

Load paths like a straight path and under an impact belts stretch by a lot so it better to keep all the fibres of the belt material as straight as possible for maximum energy absorbtion.

 

I would mount the harness direct to the harness bar or run them back at a shallow angle to the parcel shelf (try to get the fixings below the top edge with folded corner reinforcing on the engine bay side to spread the fixing loads).

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I wouldn't hold this up as the ideal solution (and the photo is less than the clearest illustration of it), but I also prefer the straight run of belt to the bent over the harness bar style and agree that attaching to the harness bar on the cage is even better. Until I have a harness bar added to my cage (nicely powder coated cage), I used what is already a very strong mount point, being the factory rear shoulder belt mounts. You can see the eye bolts at the edges of this pic.

 

DSC01508.jpg

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I managed to get Safety Devices to make me a rear cage incorporating a harness bar, the structure is designed so that the shoulder straps can be fixed directly to the harness bar.

I have used the rear lap belt holes (7/16”) and run the shoulder straps over the bar.

 

PICT0175.jpg

That's more like a third cage, rather than a half cage surely ? The harness bar is normally much higher and further forward (basically spanning the gap between the stock seatbelt shoulder mounts). In this (better ?) location the distance between the seat slots and the bar is much shorter.

 

In the pictured (lower) bar location (between the rear wheel arches) the harness belts are forced to connect to the rear factory (lap) seatbelt anchor point (rather than than anywhere higher up on the rear firewall) as this is the only point that will allow the horizontal bar to give any support to the belts OR to the bar itself, which to my mind is too low to achieve the desired effect. :twocents:

Edited by GaryH
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So you're currently running your belts through the seat slots with no guide bar behind RB :huh: ?

 

Yes - because the belts are almost perfectly horizontal. There is no need for any guide.

 

I managed to get Safety Devices to make me a rear cage incorporating a harness bar, the structure is designed so that the shoulder straps can be fixed directly to the harness bar.

I have used the rear lap belt holes (7/16”) and run the shoulder straps over the bar.

 

PICT0175.jpg

 

Thinking about it, I think this probably meets all the relevant guidelines and looks OK.

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I'm not convnced this is a good installatiion, harness bars are a good idea but but putting a bend in the seat belts is not so good.

 

Load paths like a straight path and under an impact belts stretch by a lot so it better to keep all the fibres of the belt material as straight as possible for maximum energy absorbtion.

 

I would mount the harness direct to the harness bar or run them back at a shallow angle to the parcel shelf (try to get the fixings below the top edge with folded corner reinforcing on the engine bay side to spread the fixing loads).

I agree, you are probably right, it would be better to keep the fibres straight but these are 3 inch wide heavy duty straps.

Car manufactures put far more strain on thin 2 inch webbing with conventional factory fit 3 point seat belts.

The harness manufacturer (TRS) state that it is OK to loop the harness around the bar without causing failure.

The other option would be to strengthen the rear shelf and have the harness straps horizontal. I don’t like this option as loads are applied to a part of the car that has not been designed to withstand high loads.

I chose the rear lap belt anchors as they locate on a very secure part of the car.

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That's more like a third cage, rather than a half cage surely ? The harness bar is normally much higher and further forward (basically spanning the gap between the stock seatbelt shoulder mounts). In this (better ?) location the distance between the seat slots and the bar is much shorter.

 

In the pictured (lower) bar location (between the rear wheel arches) the harness belts are forced to connect to the rear factory (lap) seatbelt anchor point (rather than than anywhere higher up on the rear firewall) as this is the only point that will allow the horizontal bar to give any support to the belts OR to the bar itself, which to my mind is too low to achieve the desired effect. :twocents:

 

Technically it does cover about 1/3 of the car but I always though these were called ½ cages or rear cages.

 

Perhaps the photo doesn’t show enough detail.

 

When I sit in the car with shoulder straps fitted the line is about 12 degree from the horizontal.

Welded harness bars are designed to have the harness straps anchored around the tube without any other fixing points.

 

I know Safety Devices are not everyone’s favourite manufacturer but they are very knowledgeable about their products.

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There's a good article on this topic in the latest MSA magazine, www.msauk.org. Imaginatively titled 'how do I fit my ROPS correctly?'

Free to access the article online but I can't put a direct link up at the mo.

Edited by BenC
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Hope this doesn't come across as being patronising but I've seen first hand how effective good safety can be when everything goes horribly wrong.

 

Ignoring personal impact damage with car or scenery, in a head on shunt there are a number of ways of meeting your maker from deceleration forces alone. Your head can detach from your spine (quite common before the HANS device was invented), or if you want to get technical another is subintimal hematoma of the aorta ie detaching the heart from its outlet to the rest of your body, or your braining smashing into the inside of your skull, or rupturing your internal organs or not that it matters a combination of these.

 

In a big off, race harnesses stretch by 20-30% to help slow down your deceleration which increase your chances of survival. Assumming everything is anchored securely, bends in seat belt runs, steep angles from horizontal, not symetrical and twists aren't doing you any favours on letting your seat belts do their job as effectively as they could do.

 

It would sadden me to read about someone leaving our little group just because they didn't know how to fit or thought it too expensive to fit safety gear properly. Its not just about how much you spend, its also about how well you fit what you've bought.

 

If in dount ask the seat belt company, roll cage company, an MSA scrutineer, a car build specialist with race experience for advice and never just copy another installation unless you know its 100% right as when you find out its wrong it maybe too late.

 

Now during the winter is a good time to review your safety kit and maybe make a few changes or upgrades, you won't regret doing it.

 

Another public service safety announcement from someone that gives a F**K

Edited by World Citizen
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MSa and FIa regulations actually state that the rear mounting point should be no more than 30 degrees below the holes in the seat, and actually running them direct to the floor is almost as bad as the above installation, there is a harness bar in the car, use it for what its designed for before you have a big shunt and seriously hurt yourself Richard..

 

Well, these aren't mine but with respect, you are getting confused. The 30 degree point is valid and important and pretty much all guides and regs specify this. But the point is 30 degrees to horizontal where it meets the seat back and these are about 12 degrees at this point so they meet that guideline/rule. If the belt went str from the rear lap belt mount to the seat back, I would agree with you as the seat back is not designed to take a vertical loading and can break (and break your back) but the whole idea of the horizontal harness bar is make sure the belts run close to horizontal into the seat back. The point of the 30 degree rule is to not load the seat back. Would it be better if the belt was mounted to the bar? Yes, given Stephan's points, but it seems marginal to me so long as you are not introducing a really long extra run of belt that adds to the stretching factor.

 

This is an extract from Schroth guidelines that are the most often quoted and clearly envisage routing over a bar and down to the floor.

 

Shoulder belts must run from the shoulders horizontally or down, at no more than a 20° angle.

In cases where the shoulder belts must be routed down to the chassis floor, support by a roll cage bar or harness guide at the appropriate height is essential to establish the horizontal shoulder strap routing off the shoulder/HANS®. Most racing seats are not designed and tested to carry shoulder belt crash loads from downward installation. Severe injury or death could result. A 45° downward shoulder belt installation is possible with seats that SCHROTH has positively tested to take a load measured during a 50 kph [31 mph] and 28 G impact with a 75 kg (175 lb) dummy. Refer to the list of SCHROTH approved racing seats in section “About Seats”. WARNING: 45° downward shoulder belt installation is not recommended with HANS®.

For the best restraint of the occupant’s upper torso, ideal anchor points should not be further back than 200 mm [8”] from back of user’s seat.

 

And as for attaching them to the top belt mount on the rear 1/4 that is as bad, in a shunt you would get twisted round as there is no straight Pull on the seat, non of us think we are going to have accidents but when it goes wrong you need to give yourself the best chance guys, dont mess around with safety items.

 

This is a fair point and I thought about it a lot when I was thinking where to mount the harnesses but maybe need to think some more. I recognise its not ideal but decided I was ok with it for 2 reasons. First and most importantly, its a pretty small angle - smaller than it looks in the photo. Secondly, I decided seats must be designed to deal with some side loading. It would be irrational if they are not as they have to stand up to forces from all/any direction in an accident and they are usually used with a 3 point lap and sash belt that by its very nature can put a twisting load on the seat. I also needed to balance using a strong factory hardpoint with using a less strong plate behind/under the parcel shelf. If the truth is to be told, I am probably more concerned about the length of the harness straps and potential stretch in an accident, given the proximity of the front cage and given I sit close to the wheel. So, I understand what you are saying, I will change it, but I am not as concerned as you are about it :)

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Leaving aside my harnesses (which I clearly stated were not ideal in the original post), where on the rear parcel shelf would you choose to mount eyebolts? On the vertical or horizontal? Or doesn't matter as long as you get close to the crease where the 2 meet? And how big a load spreader is required behind the parcel shelf? Willans sell a 55mmx55mm spreader and OMP sell an 80mmx50mm one. Sufficient?

 

Starter for 10 - the bolts should be mounted in tension not shear.

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interesting replies lads, very interesting.

 

without getting into the whole should you be in a car with harnesses but no roll over protection i'm thinking in the short term i may just go for the brey krause harness bar, the one that goes inbetween the seatbelt mounting points on the b pillars.

 

does anyone use one of these? do they offset back so that the front seats can be fully moved back?

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...should you be in a car with harnesses but no roll over protection ?

IMO, no ! You only planning to roll the car in the medium to long-term then :whistling: ?

 

does anyone use one of these? do they offset back so that the front seats can be fully moved back?

I've used one in the past, but only as a secure mounting point for a trackday video camera, not with harnesses (see above ;)). Yes they are offset and the seats can be moved fully back.

Edited by GaryH
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