BuGsBuNnY Posted May 8, 2006 Share Posted May 8, 2006 This is not correct! The main purpose of a harness is to keep you in the seat in any form of accident. the best mounting point for the shoulder straps is below shoulder level because if the vehicle rolls it keeps you in the seat better and stops you slipping upwards. You dont move an inch even if they are higher if you roll... (dont ask how I know ) If they are below shoulder level, your shoulders effectively become mounting points in case of an accident. The harness will push you down and compress your spine. Some people get away with it (see rallycars) because the harnesses go through holes in the top of the seat, which are rated for strength to act as mounting points. Quote Link to comment Share on other sites More sharing options...
Liam Posted May 8, 2006 Share Posted May 8, 2006 From memory of SVA, the minimum height of the anchorage is a point 450mm, measured vertically, above a datum 53mm in height and 136mm forward of the point where the seat cushion meets the back. (I've no idea how they do it with Playskool type seats with no definable back/seat join) At SVA (at Leighton Buzzard) they used to use a Heath Robinson device, called Nigel, that consisted of a wooden block (of the above dimensions) and a pole 450mm high, on a base that sat on the block. Attached to the top of the pole was a piece of string with a spirit level attached to it that they led to the seat belt mounting. The string had to slope downwards from the mounting towards the cockpit. I know because I failed on it Quote Link to comment Share on other sites More sharing options...
Darren B Posted May 8, 2006 Share Posted May 8, 2006 If it helps the discussion then page 254 of the Blue book states that the preferred shoulder harness direction is + or - 10 deg of horizontal, with an 'acceptable' range down to 45 deg below horizontal. Quote Link to comment Share on other sites More sharing options...
Mark Stanton Posted May 8, 2006 Share Posted May 8, 2006 This is interestin perhaps one thing to bear in mind is that SVA requirements will probably differ from that of MSA so perhaps best not to use MSA for when putting through an SVA test (see rallycars) because the harnesses go through holes in the top of the seat, which are rated for strength to act as mounting points. how do you envisage the seat acting as a mounting point for seatbelts with harnesses passing through holes this also applies to many westfields where harnesses pass through seat holes into mounting points on chassis Quote Link to comment Share on other sites More sharing options...
BuGsBuNnY Posted May 8, 2006 Share Posted May 8, 2006 I 'll describe it as best I can... Lets assume the eylets are lower than the seat holes and your back (assuming shoulders are lower than seat holes) ...In case of an accident (head on collision) your body tries to move forward. The harness tries to keep it in place. However, as you body moves forward it puts pressure on the seat holes as the harness stretches between chassis/cage mounting points and your shoulders. If the seat hole surround is not up to job, it will shear, the harnesses will slice through it and push your shoulders down, hence compressing your spine. In addition, compressing your spine is problem no. 1, problem no. 2 is the fact that the harnesses are now some cms longer as they sliced through the seat + normal crash stretch so you may hit your head on the steering wheel. Not the best description ever and an extreme case, but I hope you get my point and the theory behind it. All this was explained to me by a former WRC Skoda engineer who has been working with the team as a safety expert. Quote Link to comment Share on other sites More sharing options...
nikpro Posted May 8, 2006 Share Posted May 8, 2006 If it helps the discussion then page 254 of the Blue book states that the preferred shoulder harness direction is + or - 10 deg of horizontal, with an 'acceptable' range down to 45 deg below horizontal. If it is safer to mount the harness higher why does the blue book state that an acceptable level is 45 deg. below horizontal - NOT ABOVE! I really don't see how you can compress the spine by mounting the belts lower - forces act in straight lines; if you crash head on your sholders are moving foward; the harness does not provide any force it just stops the foward movement. The only way a harness can compress your spine is if your is moving up to your shoulders - a harness is justa static object that doesn't push or pull; just restrains. Maybee everyone has got it wrong in motorsport and we should be attaching the harness to the roof of the rally cars - its easy to put spreader plates into the roof or mounts into the top of the cage. I think you are wrong and will stick with the original of either shoulder level or lower. Quote Link to comment Share on other sites More sharing options...
Peter M Posted May 8, 2006 Share Posted May 8, 2006 I think it maybe in a motorsport accident you are more like to be involved in a accident that is going to cause the car to roll,where in a road car you are more likely to hit some head on.Thats why its different. Quote Link to comment Share on other sites More sharing options...
nikpro Posted May 8, 2006 Share Posted May 8, 2006 The harness will push you down and compress your spine. As previously stated; either Isaac Newton got it wrong or this is cr*p! The harness is incapable of pushing you down! Quote Link to comment Share on other sites More sharing options...
MikeR Posted May 8, 2006 Share Posted May 8, 2006 I can only quote what a member of the locost email list a number of years said. He was a traffic police man and was requested to review the last 10 (i think) years accidents and categories them. He then had some involvement in the SVA process. Back then we all asked him questions about the "silly" sva rules and patiently explained every one. After he'd explained it, we all realised what the point was. I raised this question. I'm not going to claim to understand the phsyics / anatomy of the answer but. If your seat belt is mounted lower than your shoulders as your weight moves forwards in a crash your spine bends ( i guess due to the lap belts holding you in place). This is a huge force and can snap your spinal cord. I believe in an ideal world you want the seat belt a smidgen lower (the 10 degrees sounds right) and I'm aiming for about an inch lower than my back. Due to the fact the sva can't measure every driver they took a arbitary figure and that is what they measure. At the end of the day why do you have a seat belt and why is the SVA there? If you're not bothered then ignore this. Me, i've rolled a car, i want to be firmly and safely planted in my chassis so i've got 6 point, 3 inch, FIA harness. If you find the australian rules they are very specific about this with angles depending on how close the mounting point is to your back. Quote Link to comment Share on other sites More sharing options...
Peter M Posted May 8, 2006 Share Posted May 8, 2006 With a seat belt mounting level or above shoulder height there is less pulling down on shoulders in an event of a head on collision than on a seatbelt that is mounted below shoulder line. This is because as the body moves forward in a collision with a seat belt mounted to low it as a pulling down effect on shoulders due to the mount be being below shoulder height ,this cannot happen if the mounting is level or above shoulder height. Quote Link to comment Share on other sites More sharing options...
BuGsBuNnY Posted May 9, 2006 Share Posted May 9, 2006 The harness will push you down and compress your spine. As previously stated; either Isaac Newton got it wrong or this is cr*p! The harness is incapable of pushing you down! Dont get upset. My description is not 100% but I think you can understand what I mean. Mike R's post may go some way to explaining it further... Quote Link to comment Share on other sites More sharing options...
Westfieldman Posted May 9, 2006 Share Posted May 9, 2006 If you mount them above your shoulder in a big head on you will brake your collar bones If mounted below your shoulder you probably won't Does that help Quote Link to comment Share on other sites More sharing options...
MAT1800 Posted May 9, 2006 Share Posted May 9, 2006 If the belts were mounted below your shoulders, as your weight pushed forwards in a crash, the belts woulld try to straighten because of the force you put on them. So they could put a similar force on your shoulders as they attempt to straighten. ? ? Seems to make sense to me. Quote Link to comment Share on other sites More sharing options...
nikpro Posted May 9, 2006 Share Posted May 9, 2006 With a seat belt mounting level or above shoulder height there is less pulling down on shoulders in an event of a head on collision than on a seatbelt that is mounted below shoulder line. This is because as the body moves forward in a collision with a seat belt mounted to low it as a pulling down effect on shoulders due to the mount be being below shoulder height ,this cannot happen if the mounting is level or above shoulder height. This is my point; the seat belt DOES NOT DO ANY PULLING WHATSOEVER (Unless it has active tensioners). If your shoulders are travelling foward the seat belt applies the same force as your shoulders but in exactly the opposite direction. All it does is restrain you; and this is done best with the mounts at or lower than shoulder height. Quote Link to comment Share on other sites More sharing options...
MikeR Posted May 9, 2006 Share Posted May 9, 2006 let me phrase it another way. The belt is soft and will take the easiest shape it can. Push something squishy into it and it will form a round shape as thats the most efficient. You're body is squishy (ish). push into the belt and it will try to form a round shape. If the belt mounting if below your shoulders think how round that shape is going to be, there goes your back. Mount above the shoulders and the round squishy shape isn't that accute, there go your shoulders / ribs / other bits the belts are holding and it hurts like hell (mate broke his in a crash). (just made this up as i had a sudden flash or inspiration and it seemed to fit) I'm guessing the 10% business is a leway as your body can squish a bit and not break. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.