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Thread: Miata, tall driver, harness angles, seat brace, ACK!

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    Default Miata, tall driver, harness angles, seat brace, ACK!

    Trying to be as safe as possible over here.

    I'm a new (~12 event) HPDE driver tracking a normal 1.6 miata. I'm slow (~6 seconds off SM pace) but I don't think that's relevant.

    Current safety gear setup: Blackbird Fabworx SD Bar, Racequip 6pt harness, 15" Kirkey 71-series Containment seat (link), and HJC AR-III helmet with HANS III 20.

    After reading a few HPDE safety threads on this board, I've been inclined to check and re-check everything to be as safe as possible.

    Two issues:

    1) My Aluminum race seat is NOT braced.
    2) My Shoulder harness angles are positive.

    Before I explain - I know that the right way to fix all of this is to just drop my car at a custom race shop and have everything fabbed to my body. I *am* saving towards this. I just want to be as safe as possible while I save for a fully caged race car with fire system, etc.

    So, my seat is bolted through my floor with 8x Grade 8 bolts with large fender washers. I'm using kirkey brackets with 4x Grade 8 bolts through the sides to secure it.

    Rear view: https://i.imgur.com/icuzKA7.jpg

    I understand the proper way to secure the rear of the seat is with the Kirkey Bracket sold here and a clamp like this. The issue is that because I am using a bolt-in rollbar with an integrated harness bar, the distance between the mounting location for the brace and the bar is quite large in the vertical direction. Am I to assume the only solution is to have a very long connection between these locations?

    The harness bar location presents the second problem. Because I am 6'2, I have the seat bolted directly to the floor. This sets my shoulders up in a way where my harness angle is not ideal per the SFI guide that was shipped with my harness. I checked the lap belt with a digital inclinometer and previously though that I verified a true 0* or better shoulder belt angle, but then realized that the slot in the seat was actually touching the harness which led to a bad reading.

    I adjusted the seat up a notch which the way it is shown above in the rear view (harness no longer touches seat when being passed through). I'm having a hard time getting a true inclinometer reading on the shoulder belt while wearing my HANS, but I think its about 5* POSITIVE.

    Like I said, SFI guide here states 0 to minus 20: http://www.gforce.com/pdf/Harness_Install_Info.pdf

    However, I also found a full explanation of the shoulder belt angles here (also from SFI). It explains the upsides and downsides of having a belt that is too low or high: http://www.jegs.com/instructions/471...essinstall.pdf

    The end attachments of the shoulder harness must also be installed at appropriate angles. The ideal position is anywhere between 5° below and 30° above the driver’s shoulder, as seen in part C of Figure 2.
    If the upper attachment point falls significantly below the driver's shoulder, then a spinal compression injury is likely to occur. In an accident situation, the shoulder belts pull down and back on the torso as they resist the forward motion of the driver. The resultant restraint force compresses the spinal col-
    umn and will add to the stresses in the spine already caused by the force of the crash impact.
    On the other hand, if the trailing ends of the harness are too far above the shoulder (greater than 30°), then two problems can occur. First, tension in the shoulder har- ness is increased and undue stress is applied to the harness and its structural attach- ments. Second, excessive angle will cause excessive motion. If the harness belts are too far above the shoulder, they will provide little resistance to forward motion of the dri- ver’s upper torso. The result is impact with the steering wheel and the possibility of neck injury. The shoulder straps should also be 3-6” apart behind the driver's neck to prevent slippage off the shoulders.
    So what gives? Is it supposed to be -5 to 30 positive, or -20 to 0 degrees? Does wearing a HANS influence this number?
    Last edited by Blaise; 10-02-2017 at 04:58 AM.

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    Senior Member fatbillybob's Avatar
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    Quote Originally Posted by Blaise View Post
    Two issues:

    1) My Aluminum race seat is NOT braced.
    2) My Shoulder harness angles are positive.

    Does wearing a HANS influence this number?
    The back brace you show is the right kind of brace. I hate back poker braces that are a pole connected to the harness bar. Yes HANS will raise shoulder height about 1" so you need to check belt path on shoulder again with HANS. Discounting the belt path through the seat you can adjust the shoulder anchor point very easy on the harness bar by how you wrap or adding eye bolt above or below the harness bar. Converting to an eye bolt and clip in harness can change the shoulder height over 5" on a 1.75" bar. When I do this I drill the bar and sleeve it then bolt the eye bolts in. Or I will weld the eye bolt foot to the bar. A clip in style on eye bolts will also hold the belt in position especially because you don't have 2 shoulder harness holes in the seat. You can also see moti of blackbird fabworks and he can not only fabricate the back brace to fit properly but also reinforce how your seat is bolted to the floor. Would you jack your car up from the floor pan under your seat? If that metal buckles under jacking the anchor points are not secure even with big washers. A 50G crash pulse is 45mph. So now you weigh 10,000lbs! Are your anchors good enough for that? I have never seen a floor that did not need reinforcing if you are going to bolt your seat to it.
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    How can you wrap the harness for it to line up with the bottom the bar rather than the middle? That alone might be enough.

    Drilling a hole to add a clip-in harness is a great idea! I thought I was going to have to weld in something like this:

    https://i.imgur.com/DLMba75.jpg

    OK, so that solves one problem. What I meant was not whether the HANS changes harness path (duh) but whether the HANS requires a lower shoulder belt angle. I did notice that if I hit my head forward (under my own power) I can move the HANS down my torso (end up being slouched). Definitely not something I should be able to do, so I'm hoping once the angles are better it'll stay in place!

    As for the rear brace, I guess I'm stuck buying some tall aluminum stock and fabricating a larger-than-normal-brace, eh? Thanks!
    Last edited by Blaise; 10-02-2017 at 04:59 AM.

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    Quote Originally Posted by fatbillybob View Post
    I have never seen a floor that did not need reinforcing if you are going to bolt your seat to it.
    Sorry, missed this and didn't respond.

    Presently the seat is mounted at the base with 2x the number of fasteners required, with large fender washers. The two bolt patterns straddle the frame rails and frame rail reinforcement kit which does indeed act as a jacking point. I'm not sure of the gauge of metal used on the miata floor pan but given the fact that I am looking to brace the rear of the seat and all the nice bends around it, I'm not sure if modifying the floor more makes sense. I certainly could ask some friends who are stress analysts! Like I said, I'm saving for a proper custom build but for the time being I'm trying to make the car as safe as possible. Photo of underneath:

    https://imgur.com/8jneWgq

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    Quote Originally Posted by Blaise View Post
    How can you wrap the harness for it to line up with the bottom the bar rather than the middle? That alone might be enough.

    Drilling a hole to add a clip-in harness is a great idea! I thought I was going to have to weld in something like this:

    https://i.imgur.com/DLMba75.jpg

    OK, so that solves one problem. What I meant was not whether the HANS changes harness path (duh) but whether the HANS requires a lower shoulder belt angle. I did notice that if I hit my head forward (under my own power) I can move the HANS down my torso (end up being slouched). Definitely not something I should be able to do, so I'm hoping once the angles are better it'll stay in place!

    As for the rear brace, I guess I'm stuck buying some tall aluminum stock and fabricating a larger-than-normal-brace, eh? Thanks!

    When you wrap with the 3 bar slider up vs. 3 bar slider down you gain or loose about 1/2" of height on a 1.75" bar. It is just how it cinches up on the bar. Sometimes every little bit helps. That image you show is for double shoulderbelt hans. That is the belt system that uses 4 shoulder straps. I use that system over 10 or 15 years now. It is almost universally used in F1 and some NASCAR guys. It is an $800 set of belts but the most comfortable HANS system and slightly better Hans function according to Dr. Melvin of GM motorsports co-developer with Downing. But those belts are a pain to use and a pain to install proeprly

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    Quote Originally Posted by Blaise View Post
    Sorry, missed this and didn't respond.

    Presently the seat is mounted at the base with 2x the number of fasteners required, with large fender washers. The two bolt patterns straddle the frame rails and frame rail reinforcement kit which does indeed act as a jacking point. I'm not sure of the gauge of metal used on the miata floor pan but given the fact that I am looking to brace the rear of the seat and all the nice bends around it, I'm not sure if modifying the floor more makes sense. I certainly could ask some friends who are stress analysts! Like I said, I'm saving for a proper custom build but for the time being I'm trying to make the car as safe as possible. Photo of underneath:

    https://imgur.com/8jneWgq
    I can't tell from your pictures. We have evolved in safety from the time the idea was to be thrown from the car to today's concept of extreme containment. Everything is about how the safety systems contains the driver. So the bottom line is if the floor can buckle and the seat move then the belts can no longer do their job and your safety system has failed. That's why the best cages have the seat integrated with the cage so that if the car disintegrates you are in the safety cell contained. That's why modern DTM and NASCAR look so much like an F1 monocoque on the inside around the driver. The more we duplicate that with our budgets the better off we will be. Also, cars with 800hp and light weight like a GT1 car make that harder than a heavy low power SCCA T4 car with OEM crush zones designed and tested on top of containment seats and cage nets etc.

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    You should really consult Moti in Socal. He is a pro and is building the best safety systems for guys like us on real people's budgets. TC design I think is in NorCal, also on trackHQ is pretty quite on this forum but I have seen some of his work too and it is very good. There is a lot of junk out there so when you do decide to add the cage pick a good builder. There are so few. You need more than welding skills and some "builders" don't even have those.

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    Quote Originally Posted by fatbillybob View Post
    When you wrap with the 3 bar slider up vs. 3 bar slider down you gain or loose about 1/2" of height on a 1.75" bar. It is just how it cinches up on the bar.
    Can you please link me to how this should look? I'm sorry but as somebody who is relatively new to this I'm having trouble finding a good diagram! Thanks!

    I will reach out to Moti today (he built my bar) to see if he has a solution for the brace.

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    I have that same seat in my car and I've used Kirkey seats in the last two cars I've built. In my present car I had Blackbird Fabworx build the cage and do the seat mounting, and the way Moti did it is brilliant. It doesn't budge a millimeter and yet it comes out so easily with four bolts.

    My old car had a seat bolted in the same way as yours. I would recommend making some thick steel or aluminum plates with the same bolt pattern as the underside of the car. That spreads the load better than fender washers. I had the same setup in my old car and it took a huge hit and the seat held. The floor didn't tear at all.

    If you are still saving for professional fab work, I recommend this seat brace from AutoPower. It's also what held my seat in during that crash. When you have enough cash, get the fab work done by a pro. Two of the best are sponsors of this forum.

    vignetteDSC_2864.jpg

    vignettedsc_2864.png

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    That's the same brace (design anyway - it was Competition Engineering item) I ordered back in June. The order has been delayed a bunch of times... I wonder if there's any vendors that actually stock it. Amazon was the wrong call!

    I'm definitely still saving up. I had started the year thinking that a roll bar with a lowered stock seat would be plenty as far as safety, and to just drive to the track to start.

    Since then I've purchased two race seats and harnesses, a HANS, newer helmet, 16 HPDE events, brakes, tires... a pickup truck..... borrowing a trailer for now. So I'm just trying to make my current setup as safe as possible. Once the trailer is purchased I can save for a properly built racecar.

    I cannot possibly work more overtime. It's been an expensive year!!!!!!
    Last edited by Blaise; 10-02-2017 at 11:31 AM.
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    Just order it from a TrackHQ.com sponsor!

    Autopower Seat Brace For 1.75 inch tubing for Miata

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    Don't use that Auto Power brace. Have a custom seat back brace built and you'll be much safer. I've seen at least a dozen of the autopower braces break where the two collar clamps are welded together. Not good.
    AiM Data and Video systems, Suspension Setup, Race car builds, support, and rentals. At your beck and call.

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    Don't use that Auto Power brace. Have a custom seat back brace built and you'll be much safer. I've seen at least a dozen of the autopower braces break where the two collar clamps are welded together. Not good.
    Although I haven't seen the failures - I can definitely see from that design that all of the forces to the seatback are focused on that weld - which is only as wide of the clamping collar (.625" at most ?) and simply doesn't seem safe.

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    Any insight on harness angles?

    I mocked up drilling and bolting up my belts at the bottom of my harness bar and it does indeed look like it will give me negative angles, which is good. I'll do some calculations (100G?) on the tube to be sure it's good.

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    Totally like/respect your quest to be as safe as possible. For the shoulder belts, I would follow the expert advice of the manufacturers and try to get as close to a -10-degree downward angle even if you need to add a bar to the existing cage structure. In my mind, a wrap on a spec wall-thickness bar is the preferred design. In some cases attaching an eye bolt may work but the bar would need to be drilled AND PROPERLY SLEEVED to make this a viable option. For most applications, I would surmise that adding a bar at the right height may be easier than drilling/sleeving (welding) an existing bar.

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    There's nowhere to add a bar unless I cut the car up and have a custom cage welded in.

    What's the proper way to sleeve the bar? I had a friend do an FEA analysis assuming 80ksi yield, with a 100g impact at 200lb BW and roughly equal distribution between belts and it passed.

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