1997 Mazda MX-5 Miata: Blackbird Fabworx Is Replacing The Seat, Pt. II'
October 17, 2012
Replacing the stock seat in a first-gen Miata that sees hard use is a decision that is easy to make and a royal pain to execute. That's why we enlisted Blackbird Fabworx to do the heavy lifting when it came to doing just that for Project Miata, our 1997 Mazda MX-5 Miata project car.
It was time. The stock driver seat was in sad shape from age and use, made worse when the foam in the bottom cushion was scooped out, turning it into an uncomfortable ass sling (as opposed to a comfortable one?). It also did little to secure the driver in place when probing Project Miata's 1.03-g cornering capability. The last straw was that stock headrest is just too low for taller drivers on staff.
Sounds like a simple problem statement to address -- unbolt the old, bolt in the new -- until you realize just how cramped the Miata cabin is. Miatas have among the least space available in the seat area(s) of any modern car. There's no width in the seat floor region, and headroom is already at a premium. Worse, the trans tunnel only eats up more space as you go forward, making it tighter still. It turns out that despite its aformentioned shortcomings, the stock seat is really a well-designed piece when it comes to making the most of the nonexistent space in the car.
The limited real estate really narrows the choice of non-stock seat -- and the seat itself -- significantly. It also means you really really need someone who is handy with a welder and fabrication tools to get a new seat to properly fit in your Miata. Moti of Blackbird Fabworx is well-versed the nuances of squeezing -- figuratively speaking -- 10 pounds of seat into the Miata's 5-pound cabin.
In our case, not only does the seat need to fit in the car, but we've complicated the fitment situation exponentially with the need for sliders -- our seat accommodates drivers of different dimensions, so needs to move fore and aft. We also want to retain a 3-point belt for street use while integrating a 6-pt harness for track use. Turns out that this combination of needs is a bit unusual -- Moti says his Miata customers coming to him for a dual-purpose seat always do a fixed (non-slider) installation and just use the 5 or 6-point belt on the street.
The seat from a Lotus Elise is one somewhat-common swap among Miata owners. It's a wispy little thing that plays rather well with the tight confines of the Miata cockpit. We considered the Elise seat for about six milliseconds before ruling it out -- Elise seats are horrifically uncomfortable, and have no provision for a harness' crotch strap besides (on that note, never never nevernevernever run a harness without a crotch strap, unless it's one of those specialized Schroth anti-submarine 4-point harnesses). Some guys cut a hole in Elise seat's bottom, but that doesn't do the structural integrity of the seat any favors. And you'd still be stuck with an iron maiden of a seat.
After talking over our situation with Moti, we agreed that a single-piece FIA shell was the most prudent course of action. FIA-certified seats are required for motorsports use, but that's not why we're interested in them in this case. The reason is safety -- FIA seats must pass a specific set of rigid safety requirements. A single-piece shell would also be lighter than stock, a nice upside.
After years of seeing and dealing with motorsports equipment of all brands, Moti has become partial to Cobra seats. For Project Miata, at first Moti tried a Cobra Imola -- a seat on the tamer end of their range in terms of aggressiveness -- but as its widest point is at the bottom of the seat, the Imola was incompatible with the trans tunnel when slid forward on the sliders. So we got on the horn with HMS Motorsport and ordered a Suzuka, a seat that's one notch up on the bolster scale, in order to have a seat that would actually play nicely with our car. Again, if you're planning a seat install in your Miata for yourself, you don't really need sliders, so you will have more freedom of seat choice than we did.
To get the new seat as low as possible, Moti removed the stock lumps and bumps comprising the factory mounts that were spot-welded to the floor and integrated steel reinforcements to serve as the new seats mounting points.
Then there was the endless tweaking and massaging of the side mounts and Recaro sliders to get all the bits to live harmoniously... yeah, we're really glad to not to have to do this ourselves. Moti also cuts (to re-shape) and welds reinforcements into (for obvious reasons) the trans tunnel in order to gain some width and to center the seat on the steering wheel -- if you don't do this, your Miata seat will be offset relative to the wheel!
The shoulder belts are anchored to the GT3 roll bar's harness bar (the collar prevents the belts from walking down the bar). As noted in a previous post, shoulder belts should be run from the shoulders horizontally or down (never up), at no more than a 20-degree angle.
There's a long list of a regulations that Moti adheres to in the integration of an FIA shell. Lap belt anchor points are reinforced with substantial plates backing up the chassis' sheetmetal. Hardware is all grade 12.9 or better. Hole spacing in the side mounts has minimum spacing to prevent tear-out. And so on.
When planning a harness integration, be sure to consult the Schroth guidelines. Schroth are considered a leading authority on motorsports safety. Also, do not ever use a motorsports-style harness with a stock Miata seat -- the shoulder belts will slide off of your shoulders in an impact. I can't stress this enough -- you must install a racing seat if you want to use a multi-point harness!
And then there's this guy.
--Jason Kavanagh, Engineering Editor
Photos by Mark Takahashi
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