Back when we first were building our STS2 Miata, we did a quickie install of a pair of Kirkey economy circle track seats, both for the additional driver support and for the weight savings. We had planned to go back and do a better job on the bracketry we built in between racing trips, but never got around to it. With the new season, a rule change has gone into effect which raises the minimum weight of replacement seats and adds the mounting bracketry into that weight calculation. This negates most of the weight savings from a seat replacement.
Our initial response to the new regs was to put the stock passenger seat back in to make street driving cushier for our better half. We also threw 5 lbs worth of flooring tiles inside the seat bottom cushion on the driver’s race seat to make it legal, yet retain the awesome support it provides while competing. Today, we finally found the time to fabricate some proper bracketry that is much stronger than last year’s setup. And with the extra weight of the additional metal, we can legally remove the ballast shims.
The Kirkey seat is designed to be mounted either from the bottom or the sides. We chose to mount it from the bottom by modifying a set of original Miata seat sliders. These were leftover from our CSP days when they had a kart seat mounted to them and still had an extra cross brace attached. Our plan is to add two additional cross braces to form a box on which to mount the seat, and use two different thicknesses of material to incline the seat and clear the adjuster mechanism. For the front brace we use 3/4” steel square tube and in the rear a piece of 3/4” steel angle. After cutting to size, the rear brace is massaged with a grinder to form flats on either side which will fit it over the slider rails. The front brace requires no additional work.
With all of our pieces in hand, we bolt the rails into the car and proceed to tack-weld the two new braces into place. We’ve learned our lesson the hard way that welding can quite easily distort metal, but not when it’s held securely in place. A straightedge is then used to angle each brace slightly prior to welding so that the inclined seat will have a flat mounting surface. Once everything is solid and square, we remove the sliders and do the final welds out in the open where we can do a better job. Any screw-up here could mean injuries in the case of an accident. Satisfied with the coverage and penetration of our welds, we cover it all with a coat of black paint.
The next step is to drill mounting holes in the bracket to match those already in our seat bottom. A hand-held variable-speed drill makes quick work of that task, and we bolt everything together with some Grade 8 hardware we picked up earlier from the local Home Depot. After re-installing the seat cover, the whole unit is bolted back into the car using the stock attachment bolts/holes. Interestingly, we immediately notice a more solid feel to the whole assembly. Hopefully, we’ll never have to experience its ability to withstand the higher level forces of a sudden impact, but its nice to know that it can.
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