In a message dated 5/1/2003 7:40:03 AM Eastern Daylight Time,
npenney@mde.state.md.us writes:
Referring to my earlier post about rollbars and harnesses...
> Crushed vertebrae or ruptured spinal disc is an all to common problem
> resulting from the equally all to common improper mounting of a double
> shoulder harness rig like this one.
I would agree with you almost entirely, though I have to say I have always
been a bit suspicious of the stock Spitfire shoulder harness since it still
goes up and over the seat back unlike modern setups that have a higher
mounting point or a loop. James' injuries also indicate that the stock setup
is not very effective.
>
> On the stock 3 point harness the shoulder harness has its mount up
> roughly even with the shoulder, preventing downward forces. A racing
> application of the double shoulder harness rig requires both shoulder
> straps be routed at the same shoulder height, normally over a bar on
> across the roll bar, or mounted directly to the roll bar. When a double
> harness rig is mounted by a novice, it is routinely routed from the
> floorboards directly up to the drivers shoulders, with no roll bar.
> This results in tremendous down force on the drivers shoulders in a
> collision, resulting in the spinal damage already mentioned.
>
> Without some sort of cross-chest strap, it is quite easy to get shot
> out from between the dual shoulder straps in a collision. This is why
> infant car seats have that chest clip, as do many military applications.
> The three point harness avoids this problem by crossing the body and
> having the body wrap around that cross chest strap in a collision.
> Racing cars also partially avoid this problem by their very restrictive
> seats and superior mounting of the harness (though this is far from an
> absolute). Novice mountings are made even worse by generally mounting
> one harness base to the outboard sill, the other to the transmission
> hump, resulting in a harness that is wider then the drivers shoulders,
> helping ensure ejection in a collision, though frequently not until the
> driver has had their spine at least partially crushed from the downward
> forces.
>
> Many times the shoulder straps are adjusted too short, resulting in the
> lap belt riding up in the abdomen area, and not down over the pelvis.
> This results in severe abdominal organ injuries in a crash.
>
> All harnesses (including just a 2 point lap belt) suffer from
> submarining. The more the seat is reclined, the worse the problem. A
> crotch strap (5 point harness) helps tremendously. A double crotch
> strap (6 point harness) reduces groin loading in a collision by 40% over
> the single crotch strap, and almost completely eliminates the testicle
> ruptures that can result from the single crotch strap of the 5 point
> harness.
>
> There is also a theory that a racing harness can result in more severe
> accident injury in a roll over without a roll bar then a 3 point harness
> would. The claim is that with a 3 point harness, if you are in a roll
> over accident you can crawl down under the dashboard. A racing harness
> prevents that ability. Having been in some serious crashes that
> involved a lot of vehicle motion (never rolled a car, but I did fly off
> a canyon wall once in Colorado), I find the notion of crawling around
> the passenger compartment while crashing and flipping the car upside
> down to be absurd on its face.
>
> To the above roll over concerns, most Spitfire roll bars are too low to
> do any good, so the point is moot. You are just as dead with the top 4
> inches of your body crushed as you would be with the top 24 inches of
> it crushed. As well, most Spitfire street roll bars are so poorly
> mounted as to be ineffective in a roll over, they just punch out through
> the floorboard.
I have to agree about the rollbar height as well, though, I think it's
better than no rollbar at all because it adds a little crush resistance in
some circumstances. Our plan is to secure the rollbar mounting points by
through-bolting into plates on the underside that match the size of the
interior mounting plates. If I can figure a way to attach to the chassis,
we'll do that, too.
Based on this discussion, I think we'll add shoulder harness loops that mount
on the rollbar so the stock harnesses can hang above the seat. That should
also make the harness a little easier to reach.
>
> There are also some substantial inconveniences with a more complex
> racing type harness, especially one that does not use inertial reels.
> You will no longer be able to lean over and roll down the passenger
> window, leaning forward to pull out your wallet becomes a near
> impossibility, and the job of buckling all these straps together takes
> appreciably longer than the quick buckling of the stock belt.
>
> It would have a potential advantage over the stock harness in a severe
> rear end collision. The Spitfire seat back is weak, and will collapse,
> resulting in possible ejection. The 4 point harness will do nothing to
> lessen the collapse of the seat back, but it will more likely hold the
> occupant in the car. Considering the proximity of the gas tank and the
> potential for its rupture in a collision severe enough to eject the
> passenger, I'm not sure how much is truly gained by reduced ejection
> possibilities. None the less, I would expect reduced ejection to
> result. Having been rear ended in a car that did allow for rearward
> ejection (Dodge Shadow), I can say I didn't care for it and would prefer
> automobiles that didn't come so equipped with this auto eject feature.
>
While we're on the subject, the gas tank could stand a lttle more protection.
James' toolbox seemed to help there (aside from its many other practical
applications).
Tom Burke
80 Spit (in no immediate danger of rollover)
> Make no mistake, a 3 point harness can be very effective if maintained
> properly, worn properly, and if the base vehicle has it mounted properly
> (and the Spitfire basically does).
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