4 point harness to rollcage?

Discussion in '40- & 55-Series Tech' started by slickrock, Nov 15, 2005.

  1. slickrock

    slickrock

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    Is it possible to mount the 2 shoulder straps from a 4 point harness directly to the factory rollbar cross bar? It is exactly the same height as the shoulder bolts that are on the side of the hard top. (out of a 73 FJ40). Or should I weld in a new cross bar a little lower for the shoulder mounting points?
     
  2. John Smith

    John Smith In the garage

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    You want the mount point as close to your shoulder height as possible. You want the straps horizontal as they come off your shoulers and connect to your cage.
     
  3. slickrock

    slickrock

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    Why then do regular shoulder straps rest off the shoulder at like a 45 degree + angle on all other 3 point set ups? I thought that if the strap went down, it would crack your collar bones in a wreck, but the more the straps are angled up, the better.
     
  4. John Smith

    John Smith In the garage

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    You are correct that you do not want the mount point lower than your shoulder because when in a wreck the force will want to push down and crush you. A picture can be worth a thousand words. This is a picture of a factory built cage used by the BMW factory race team in Germany. It actually does look like the mount point is somewhat above horizontal. But not by much.
    cagepic.jpg
     
    Last edited: Nov 15, 2005
  5. slickrock

    slickrock

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    Cool. Looks like I need to take out hte welder and run another bar. Thanks.
     
  6. treerootCO

    treerootCO Where are my keys?! SILVER Star

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    The ideal position is
    anywhere between 5° below
    and 30° above the driver’s
    shoulder, as seen in part C
    of Figure 2.
    If the upper attachment
    point falls significantly
    below the driver's shoulder,
    then a spinal compression
    injury is likely to occur. In
    an accident situation, the
    shoulder belts pull down
    and back on the torso as
    they resist the forward
    motion of the driver. The
    resultant restraint force
    compresses the spinal column
    and will add to the stresses in the spine already caused by the force of the crash
    impact.
    On the other hand, if the trailing ends of the harness are too far above the shoulder
    (greater than 30°), then two problems can occur. First, tension in the shoulder harness
    is increased and undue stress is applied to the harness and its structural attachments.
    Second, excessive angle will cause excessive motion. If the harness belts are too
    far above the shoulder, they will provide little resistance to forward motion of the driver’s
    upper torso. The result is impact with the steering wheel and the possibility of
    neck injury. The shoulder straps should also be 3-6” apart behind the driver's neck to
    prevent slippage off the shoulders.
    Untitled-1.jpg
     
  7. slickrock

    slickrock

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    cool. I will use that diagram when I weld in the cross tube for the 4 point. thanks
     
  8. slickrock

    slickrock

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    so this guy on thePirate Board's 4 point harness write up is wrong with his attachment points. interesting.
     
    Last edited: Feb 9, 2007
  9. camcruiser13

    camcruiser13

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    arrrgh that wood be cureckt matey
     
  10. Steve C

    Steve C

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    I'm not sure what you had in mind, but I would consider adding additional tubes at angles to the top and side tubes of the roll bar or maybe an X arrangement, rather than a single tube from one side to the other. Triangles=strong.
     
  11. treerootCO

    treerootCO Where are my keys?! SILVER Star

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    Triangles are great but keep them away from your head. What good is a roll cage if you smack your head into it.
     
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