1997 Mazda MX-5 Miata: Blackbird Fabworx GT3 6-Point Roll Bar, Part II
July 01, 2011
It turns out that Moti of Blackbird Fabworx -- father of Project Miata's brandy-new GT3 6-point roll bar -- has been building fast Miatas for the street and track for years. He started out as a hobbyist experimenting on his personal car and testing at the racetracks of southern California. Then he became a professional -- working for years at Tri-Point Engineering, a mecca of Mazda motorsports -- before finally branching out on his own.
There are things you learn when you've been around the block.
The basics of Miata roll bar geometry is largely fixed by the shape of the cabin. There's only so much wiggle room for the placement of 1.75"-diameter tubes of drawn-over-mandrel (DOM) steel.
From there, Blackbird Fabworx gets creative. Moti will vary the tubes' wall thickness depending on your needs; make it a 4-point bar; the rear bracing can be a single diagonal, dual diagonal, an X-brace, or your initials spelled out in tube segments; he'll integrate a bar that ties into the windshield header, paint the roll bar fluorescent turquoise, you name it. Within reason, of course -- don't ask for an aluminum roll bar or a 2-point job (those bars fold over the occupants like a mousetrap).
We went with the X-brace for better visibility than a dual diagonal.
What makes our GT3 roll bar a 6-pointer are its door bars, and not all door bars are created equal. Moti has seen how the commercially available door bars tie into the flimsy sheetmetal of the Miatas floor pan, and he doesnt like it.
Instead, the door bars of the GT3 roll bar tie into the car's vastly more substantial rocker sill area. Moti welds a flat receiver mount on each side of the car where the rocker meets the door frame. The door bars then bolt to these receiver mounts, forming two of the six attachment points. The other end of the door bar is welded to the base of the roll bars main hoop.
Not only is this location a much more structurally sound attachment point for the door bar than the sheetmetal of the floor, it also frees up the footwell for, well, your feet.
I originally had some concerns about ingress and egress being impeded by the door bars. It's workable. Yeah, they're there, and so are you, but it's not that big a deal. If it's too hard to get in or out, you're too old. Seriously, finding your way into the cabin of a stock Elise is more cumbersome than negotiating these door bars.
And once you're inside, the door bars are tucked so close to the door panel that they pose no impediment to your restless legs syndrome. They simply disappear.
The door bars are nearly a straight shot from the rocker to the main hoop in order to maximize stiffness. Subtle bends in the bars angle them outward so as to route them tight against the door cards. Seat travel is unaffected; it can slide all the way back. The headrest will tilt into the diagonal bar at this position.
I don't use full seat travel despite being 6'1" as I'm of the short-legs-and-long-torso people. Although it would require a very strange impact to bonk my head on the bar, I'll admit that its presence back there has got me thinking 'new seat' now more than ever.
I'd like to sit lower than our foamectomy'd seat allows. The stock seat's headrest is on the short side, and it'd be nice to have some real-life lateral support to stand up to the leech-like 1.03-g grip this thing has on the road. Yeah, I'm so over this crummy stock seat.
Although these photos don't show it, we've got high-density roll bar padding for this roll bar. Sticks of SFI 45.1 padding have been kicking around under my desk for months for this very reason.
Back to the roll bar. The tubes forming the door bars and rear X-brace are of thinner wall thickness than standard roll bar tubing to cut weight.
Same philospophy applies to the GT3's characteristic gussets at the X -- theyre lightweight 16-gauge sheetmetal that's been folded like a taco shell and then welded in to reinforce things further. Those holes are formed by a dimple die, which not only reduces weight, it actually makes each gusset stiffer by cold-working the edge of the hole out of plane.
Our entire GT3 6-point roll bar weighs 53 pounds, or barely more than commercially available 4-point roll bars. Cost was $1200 installed (add $25 for the slick 3M clear film on the door bars; consider it a must-have), which is competitive with what you'd pay for an off-the-shelf roll bar and door bars, plus shipping and installation. But then you'd have a heavier roll bar with worse door bars and no customization.
Plenty of driving impressions in posts to come. Enjoy your holiday weekend.
--Jason Kavanagh, Engineering Editor