Let me first set the stage by saying I'm not a safety engineer and that it's not my intent to make recommendations about safety equipment because I'm admittedly unqualified to do so. I've done no tests, but I have done a lot of reading. I could certainly be guilty of not analyzing the entire 'system,' mostly because I don't have the knowledge. Perhaps I'm just a guy with too much time on his hands. I should also state that with my limited knowledge, I do like the INTENT of the sys.6.pack's approach to safety, but I've got concerns about some of the details of the product.
Anyway, I've recently had an up close look at the sys.6.pack and I've made some observations I'd like to share with the forum. We should probably start with a primer on hardware and metals:
Primer On Hardware:
A fastening system is only as strong as its weakest link. Metric bolt classes come in numbers like 8.8, 10.9, and 12.9. Higher classes appear to be stronger bolts. I did come across some concerns of 'hydrogen embrittlement' with 12.9 bolts, which seems to mean that improperly manufactured 12.9 bolts can fail at tensions below their rating (so if you buy high strength hardware make sure its from a reputable place). If a nut is part of the fastening system, the article I read indicated the nut should have a rating equal to or better than the bolt. For example, a class 10.9 bolt should be paired with a class 10 nut. It could be paired with a class 12 nut, but should not be paired with a class 8 nut. For what its worth, I could not find any class 12 nuts available for purchase.
Frequently Asked Questions on Bolting Matters
American Fastener - ASTM, SAE, and ISO Grade Markings
Primer On Metals:
Metals can be classified according to their galvanic series. Any two metals that are far apart in the galvanic series chart are susceptible to galvanic corrosion in the presence of an electrolyte (water would qualify as an electrolyte). Aluminum is quite low on this chart, so if you put a different metal that was higher on the chart next to it (such as stainless steel) and add some water, you'll get galvanic corrosion , and because aluminum is the least noble of the two it will be the aluminum that corrodes. This situation can be mitigated by adding an insulator between the two metals (think paint or silicone). Many times you'll see bolts that are zinc coated - the zinc coating improves resistance to corrosion , but another important point is that zinc is much closer to aluminum on the galvanic series chart, so zinc plated hardware next to aluminum should have less chance of galvanic corrosion.
Galvanic corrosion - Wikipedia, the free encyclopedia
Galvanic series - Wikipedia, the free encyclopedia
Observations on the factory hardware:
On the drivers side of my car, the bolts on the front rails have a class of 8.8. The rear bolts and all the bolts on the passenger side were class 12.9
socket head bolts. I was not able to observe the class of whatever holds the bolts in on the other side of the aluminum. If they are nuts welded to the aluminum, the first thing that comes to mind is that I was not able to find a nut greater than class 10 (although Lotus likely has much better resources than I do).
Observations on the sector hardware:
Sector did not give me much detail on the hardware used, other than telling me its stainless steel. The button head screws included do not have any markings on them, so their class is unknown. The nuts that come with my kit are class 8, so no matter the strength of the screw, the maximum strength class of the hardware fastening the seat to the plate underneath is class 8, but it may be less than that if the bolts are stainless steel and have no class at all.
Observations on hardware in flight applications:
All I've read online suggests that AN hardware be used in flight. AN hardware is in standard units (no metric) and from what I've read, it seems to be the case that AN hardware is comparable to standard GRADE 8 that has certified lab results. The rough metric equivalent of GRADE 8 is class 10.9. Stainless steel is often NOT used in aircraft applications because aircraft tend to have alot of aluminum (see primer on metals).
Aircraft hardware and commercial hardware
What does it all mean?
Well I really don't know, other than I have concerns about the strength and type of hardware used in what looks like an otherwise good approach to adding safety to the lotus's cramped cabin. Maybe it doesn't matter because some other part of 'the system' will fail long before the hardware provided,ie maybe the bolts on the seat rails will shear long before the bolts going through the tub will separate. Maybe someone with more knowledge can fill in the gaps. It is not my intention to cast a cloud on this product, but I think swapping out the hardware that comes with the kit is an idea worth considering.