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PostPosted: May 10, 2018, 10:44 am 
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Joined: April 26, 2008, 6:06 pm
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Location: Under the weather. (Seattle)
Some seat and rollbar combinations in a Miata are considerably more likely to result in cranial impacts than others. These would be the type of design considerations I spoke of in my original reply. It would be beneficial to the conversation to know which pairing is being used for this point of comparison.

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PostPosted: May 10, 2018, 11:44 am 
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Joined: May 27, 2006, 9:46 pm
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Location: BC, Canada. eh?
As far as factory 3-point restraints are concerned, watching any crash-test videos of rear end collisions will convince you of just how much vertical movement they allow. If the underside of the roll bar is 4" above the top of your head, for example, your head WILL strike it in the event of a rear-end collision. If you hope to avoid such vertical movement, 4- to 6-point, non-retracting harnesses will be necessary. Bear in mind, too, that many such harnesses are strictly forbidden for street use in many jurisdictions.

While a solid rear-end collision itself may very easily be survivable (considering that modern cars are engineered with crush zones, to dissipate impact forces over both time & distance), a substantial cranial impact with a roll bar likely will not be survivable.

The only deformable structure involved in a head-vs-roll bar collision is the brain, and any substantive degree of deformation will have serious or fatal results.

Basically, as motorsports enthusiasts we've always been indoctrinated into the necessity of roll bars in open cars, so such a car is "incomplete" without one. However, we also need to be cognizant of "the law of unintended consequences", lest the cure be more dangerous than the disease...

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PostPosted: May 11, 2018, 10:16 am 
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Joined: December 4, 2010, 1:53 pm
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Location: Edmonton, Alberta, Canada
"Sorry to hear of your experience. Were you wearing a seatbelt with an over-shoulder element to it? You know, the kind of standard, factory-installed configuration these days."

Hi Lonnie
yes, I was wearing my over the shoulder factory seatbelt. I only use a harness on the track. It didn't help that I drive with the seat more reclined than most people.
cheers
Doug

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PostPosted: May 11, 2018, 11:11 am 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
When I was poking around on the Internet, looking for information on the best angle for the shoulder straps of my 5-point setup, I was disheartened by the disagreement over what the acceptable range of that angle should be. I figured the best info would come from racing organizations like NASCAR, FIA, SCCA, etc. I really couldn't find what I wanted. Maybe they bury it in expensive rule books that you have to buy?

I even noticed different manufacturers give different recommendations for essentially the same setup. That's a little worrying. You think there would be solid information based on testing and real-life record keeping on all these things by now.

I'll likely be back to a discussion similar to this when I design the passenger side seat of our cruiser. My wife likes to have a serious recline on the seat. We are so low and laid-back already in these cars that I feel she's going to need a submarine belt for sure. Otherwise, I feel she could end up in the footwell with any kind of substantial front end collision. I know it will be tough to get her to use it, though.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: May 11, 2018, 1:17 pm 
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Joined: April 23, 2006, 8:26 pm
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Location: SoCal
Lonnie-S wrote:
...I even noticed different manufacturers give different recommendations for essentially the same setup. That's a little worrying...

I saw the same thing, but went with what my belt manufacturer recommended.

At the end of the day, all we can do is our best, and if we want to be really safe, it means staying away from these little cars we're building!

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PostPosted: May 12, 2018, 10:55 am 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
KB58 wrote:
. . . At the end of the day, all we can do is our best, and if we want to be really safe, it means staying away from these little cars we're building!


That's so true. I always think of my build as a ". . . motorcycle that doesn't fall over." I read that here on this site, but I don't remember who said it.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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