Yet ANOTHER harness question- anchor to roll bar or rear?
12-17-2008, 08:03 PM
#16
John, no offense taken, I know you're an expert on this. I was just thinking out loud and I added that it was just my opinion and that I'm not an expert in this field. I am however an engineer, just not a rollbar and seatbelt one. 
I think you might have missed my point. My point was not that it's ok because everybody does it. I totally agree with you on that. Won't pass my filter either. My point was, since there's lots of these in use, where's the data saying these bolts fail or are likely to fail in the context of the original poster's premise - street/DE.
Due to the commentary made in this thread with regard to the small rear bolts, the OP has been steered to mounting the harnesses to the seatbelt bolt anchors and using the roll bar as a guide bar instead of mounting directly to the roll bar. In this particluar situation (dual use DE car), which of these two is better? The OP is looking for an expert opinion, so I defer to your expertise to answer that question. Again, conceding that this is not the optimal, safe setup.
Best regards,
I think you might have missed my point. My point was not that it's ok because everybody does it. I totally agree with you on that. Won't pass my filter either. My point was, since there's lots of these in use, where's the data saying these bolts fail or are likely to fail in the context of the original poster's premise - street/DE.
Due to the commentary made in this thread with regard to the small rear bolts, the OP has been steered to mounting the harnesses to the seatbelt bolt anchors and using the roll bar as a guide bar instead of mounting directly to the roll bar. In this particluar situation (dual use DE car), which of these two is better? The OP is looking for an expert opinion, so I defer to your expertise to answer that question. Again, conceding that this is not the optimal, safe setup.
Best regards,
<< All DAS bolt in roll bars mount in this same fashion. Is there data showing failure of these rear mounting bolts? This bar has been used in club racing for years prior to the cage rule and there's a bunch of them out there with harnesses directly mounted to them. Don't forget that the main hoop is bolted to the front heavy duty seat belt anchors. >>
Steve, don't take this personally. This is an example of flawed thinking in my opinion. You can find many things that "everyone does" that are patently absurd, even now. Everyone needs to be a little more critical than just following the herd on such things. I'm no engineer either, but I have developed the facility for critical thought. It's nothing but a learned response to any such situation. When I see something, I immediately run it through my filters to see if it makes sense. I don't care what anyone else thinks. That "everyone else does it" snags in my filter like a brick!
Since at the very least, we are looking to this bar to manage belt loads, common sense would tell you that the mount bolt for any bar should be at least as big as a seatbelt bolt. We know they have specs for that, and that it is an important safety item that cannot be allowed to fail. I don't know what the rear bolts are, but they are not 11mm (Porsche belt bolt size) as far as I can remember. I'd guess they are 8mm. The difference in tensile yield strength of an 8mm bolt is roughly HALF that of an 11mm bolt. This is the type of thinking one needs to do.
Beyond that, I've never liked the main hoop mounting of the DAS bars. That offset plate they use to get over to the lower lap belt mount does nothing for me. It represents an inherent weakness in the design to me, relative to something that attaches the end of the tube DIRECTLY to the mount point. Whether it would be easy to get such a mount is another matter, and precisely why they DIDN'T do it. They're mount makes it easy, not optimal.
Steve, don't take this personally. This is an example of flawed thinking in my opinion. You can find many things that "everyone does" that are patently absurd, even now. Everyone needs to be a little more critical than just following the herd on such things. I'm no engineer either, but I have developed the facility for critical thought. It's nothing but a learned response to any such situation. When I see something, I immediately run it through my filters to see if it makes sense. I don't care what anyone else thinks. That "everyone else does it" snags in my filter like a brick!
Since at the very least, we are looking to this bar to manage belt loads, common sense would tell you that the mount bolt for any bar should be at least as big as a seatbelt bolt. We know they have specs for that, and that it is an important safety item that cannot be allowed to fail. I don't know what the rear bolts are, but they are not 11mm (Porsche belt bolt size) as far as I can remember. I'd guess they are 8mm. The difference in tensile yield strength of an 8mm bolt is roughly HALF that of an 11mm bolt. This is the type of thinking one needs to do.
Beyond that, I've never liked the main hoop mounting of the DAS bars. That offset plate they use to get over to the lower lap belt mount does nothing for me. It represents an inherent weakness in the design to me, relative to something that attaches the end of the tube DIRECTLY to the mount point. Whether it would be easy to get such a mount is another matter, and precisely why they DIDN'T do it. They're mount makes it easy, not optimal.
12-18-2008, 11:05 AM
#17
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Nope. I'm just a guy. Because you're an engineer and can do all the math, YOU know in your HEAD this is not a good setup. I'm not an engineer, but I know in my GUT it is not optimal. If I had your training (not smart enough), I'd be scary!
In this instance, I'd have to say I would attach at the seat belt points, BUT ONLY WITH NYLON BELTS THAT DON'T STRETCH AS MUCH. I'd also make damn sure I didn't hit anything!!
It's either that or get a bigger bolt back there. That would be my choice, but it's not my car... or my neck.
