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Old 01-03-2007, 03:43 PM   #1
Chad W
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Default How far back can the roll bar (cage) be placed?

I share an older saab 900 with a buddy for ice racing and as we plan to move to spiked tires this year we need a roll bar and a proper harness. A friend who is an experienced welder on rock crawlers put the bar together for us, and its very solid and well designed, but I'm concerned that it is too far back from the b pillar. I know that different organizations have different rules, and that it will probably fly with the ice race league, but I'm wondering in general, in terms of effectiveness how far should the main hoop be behind the b-pillar?
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Old 01-03-2007, 03:51 PM   #2
TyrannoSullyRex
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I thought it should be within 6 inches of the driver (fore/aft), b-pillars be damned.
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Old 01-03-2007, 04:10 PM   #3
blue blurr
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The harness mounting point(harness bar) may not exceed 8" (200mm) from the back of seat/shoulder. As stated in the HANS quick start guide.
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Old 01-03-2007, 05:16 PM   #4
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6 inches makes more sense to me....

Do you think that harness bar specs are different for when you run HANS system than what is necessary for just a regular 5 point?
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Old 01-03-2007, 08:03 PM   #5
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even with belts you want them to be as short as possible.
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Old 01-04-2007, 02:16 PM   #6
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Quote:
Originally Posted by blue blurr View Post
The harness mounting point(harness bar) may not exceed 8" (200mm) from the back of seat/shoulder. As stated in the HANS quick start guide.
No one tells you can't run because you violated some manufacturer guidelines (especially when you don't even have the part in question, e.g. Hans device). They do that when you don't meet the safety RULES. The rules for SCCA and NASA say not to exceed 6" behind the drivers head.
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Old 01-04-2007, 02:45 PM   #7
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I wasn't thinking as much about the efffect of the distance of the harness bar, rather I was thinking more about the effectivenss of the main hoop at protecting me in a roll over situation.

I'm assuming that if the main hoop is too far back, it would allow for a dangerous amount of roof intrusion into the passenger compartment, is that correct?

What is the negative (safety) effect of having the harness mounting points too far back? I was always under the impression that it was the angle of the shoulder harness and not the distance that was critcal.
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Old 01-04-2007, 03:07 PM   #8
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In an accident, the harnesses stretch significantly. This elongation lengthens the time of the impact event and can render you more susceptible to other trauma. That's why the harness length should be as short as possible.

As far as where to put the main hoop, it's not like you're the first person to cage a Saab 900 - look at prior art. You could also PM RichardM here on NASIOC and ask for pictures of his design.

Cheers,
- Christian
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Old 01-04-2007, 03:23 PM   #9
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Quote:
Originally Posted by Grintch View Post
No one tells you can't run because you violated some manufacturer guidelines (especially when you don't even have the part in question, e.g. Hans device). They do that when you don't meet the safety RULES. The rules for SCCA and NASA say not to exceed 6" behind the drivers head.
That's great, I was just quoting HANS as a referance for a general idea of what the distance should be for the OP. No need to sound like a dick to someone who is just trying to help out.
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Old 01-04-2007, 11:18 PM   #10
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If you just have a bar and not a true cage the two main reasons for keeping the bar as close as possible to the seat without getting in the way of the helmet is to:

1)Reduce belt stretch. Take a look at the in-car video of some hard impacts. It's amazing how much belts stretch. You want them as short as possible.
2) Reduce risk of neck injuries from the roof collapsing. On Subarus the A-pillar and B-pillar are unusually strong but on an old Saab 900 the A-pillar in particular isn't all that stout. You want the bar as far forward as possible.

Good luck,
--Kevin H.
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Old 01-05-2007, 10:53 AM   #11
Chad W
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Thanks Kevin,

That's pretty much the info I was looking for.

The guy who put it together offered to "finish the cage" if it was too far back...as is, the main hoop is 20" behind the drivers head. Could this distance be okay if the cage was finished? My instinct is to not build on top of a bad foundation, but I'm wondering if a full cage has different criteria for main hoop positioning.

Thanks,
Chad
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Old 01-05-2007, 11:51 AM   #12
Grintch
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Quote:
Originally Posted by blue blurr View Post
That's great, I was just quoting HANS as a referance for a general idea of what the distance should be for the OP. No need to sound like a dick to someone who is just trying to help out.
The problem is that the 8" from the HANS guidlines could very easily result in a cage/rollbar that doen't meet the 6" distance required by most sanctioning bodies. I probably came on a little too strong about it, sorry. The SCCA and NASA rules are online, so when you want to know what is legal (or a good idea), that should be your first stop.

Hitting your head on the main hoop is bad, thus you want/need some seperation. Plus I think the rules prohibit having the drivers head go under the hoop.

Having the roof cave in on your head is bad, thats why you don't want too large a seperation. Plus longer harness belts stretch more, however, that is not nearly as important as the first two.
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Old 01-05-2007, 12:11 PM   #13
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Well yes, closer is better all I was doing was quoting HANS and there MAXIMUM distance of 8".
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