Adding a harness bar to a Hard Dog Deuce
 

I'm taking some time to get all my safety gear in order. That means moving from the 3-point/airbag setup to a 5-point/neck-restraint setup. The car is predominantly for street use, with 3-5 track days/year.

The roll bar I have is a Hard Dog Deuce. I like this bar for two reasons: first, I am 6'2" and need as much leg room as possible, and with my seat all the way back, it sits far back in the car, completely behind my seat. That means I won't be concussed every time I go over a speed bump while driving on the street. Second, and much less important, I keep my car in roadster-mode, and I can reach back and flip up the top without getting out of the car.
https://cimg5.ibsrv.net/gimg/www.mia...8f2373c6e0.jpg

It does not have a harness bar, and the Hard Dog harness bar doesn't fit this bar, and even if it did, would set the shoulder straps at too high an angle for my seat position.
My theory is that 99% of the load on the harness bar is in the forward direction, so a bar placed behind the main hoops would have 4 points of structural contact, and it would only have to bridge 12 inches or so on each side. If I go with this location, a square tube would have a wider contact area than round-on-round. I could get 1.5 inch 0.120 square tube and attach it with u-bolts to the 4 uprights of the main tubes. It would then be height-adjustable, and the harness shoulder straps could attach the bolt-in way.

https://cimg2.ibsrv.net/gimg/www.mia...b3a9444485.jpgWay too high because the tube is too long, but that's what I'm thinking. Also, that's 1-inch square tube, so it would be beefier.
https://cimg3.ibsrv.net/gimg/www.mia...756d19a4b3.jpgThis is angle, but you get the idea in terms of placement.

Good idea? Bad idea?

Im no expert, but i am sure others are gonna tell you to get a real roll bar...

That's what I'm expecting too. I'm open to hearing opinions from all sides and in the end I need to balance street safety with track safety.

I think rather than weld onto the main hoops, I'd want to weld on tabs that bolt into the seatbelt tower thingies. Depending on the ideal height, Welding in might make installation/removal impossible without mangling the parcel shelf. There is a horizontal bar section that rests on the frame bit in front of the gas tank.

I made a bar that bolts into the seat belt towers. More details are in my build, post 123.
Trying to post from this phone thingy:
https://cimg2.ibsrv.net/gimg/www.mia...b580771a41.jpg

Thanks! For others, here's the link: https://www.miataturbo.net/build-thr...7/#post1416928

What exactly did you bolt into? Those upright bits behind the plastic trim look super flimsy.

The seat belt towers are one of the stronger parts of the miata unibody. Certainly in the fore/aft vector. You can see in some of my pictures that the metal is doubled up 14 gauge (or whatever the thickest metal Mazda used). It might be a little hard to see, but there is also a captive 3/8" nut in the bar itself. 2 other 7/16" bolts counteract rotation and spread the load.
Disclaimer: I'm not that kind of engineer, I did not simulate or destructively test my solution, use at your own risk :fael:

I see where you are talking about now. On my roll bar the upright is just in the inside of the seatbelt tower, making the strong parts not easily accessible. I think I could weld tabs on onto the roll bar uprights to hold the square tube in place, which would be much stronger than u-bolts, but just as removable.

I'd skip it and recommend swapping roll bar to one that already has a harness bar.
Biggest reason to do that isn't actually the harness bar, it's the fact that you're running a double hoop bar that provides such minimal safety cell that you're really better off getting something with a full size hoop.

What do you mean by minimal safety cell? I understand that if I go over in gravel or something else soft, the double hoop can sink in. Are there other scenarios I'm not thinking of where this style of bar provides less protection than a full hoop bar in the same position?

Watch the slo-mo towards the end of the video and note how far out his head moves out of the "protected zone" the little hoop provides -

A full cockpit width and height roll bar buys you a much bigger cell, not just towards the outside of the car but towards the inside - the area where a car might roll over into is not necessarily flat.
BTW, the video is also a good advert for arm restraints, in case you don't have them.

That's a compelling argument...

How do you approach designing a bar that provides as large a safety cell as possible, while also keeping the bar clear of head contact for street driving? Do you make a kind of compromise bar that minimizes the downsides of both?

I'll skip the roll bar part of the question for semi-obvious reasons, but a good FIA seat goes a long way towards that, also solves your issue of unsupported alum seat at the same time.

Sorry, but to be honest I seem to not be picking up the obvious. The curiosity is real! I've tried to seek out info on my own, such as measurements similar to what Hard Dog lists so I can do a comparison, but there isn't much on your website ;)
I'm trying to solve for tallness and street use while adding safety on track. Your point about the seat is noted. I am planning to add back support to the seat as part of a harness bar if I go the DIY route. I'm open to any and all options though.

That's Blackbird Fabworx, manufacturer of rollbars. His answer would be, "just buy our roll bar." :giggle:
You are either fully protected on the track or the street. Pick one.

https://www.advanced-autosports.com/...ata-floor-drop and use normal well tested rollover protection.

Thanks for the input everyone. I've decided to get a proper roll bar and be done with it.

Soooo...how much the old one would be?

As the owner of one, it was one of the more expensive mods on my car and looks/feels great. I hope I never actually have to test it or use it.