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Jass Performance Seat Lowering Rails for the ND Miata

Jass Performance makes the only ND seat lowering option that is both adjustable and keeps the factory slider. Where Paco fixes the seat in place and Aurora makes you trim the base, the Jass rails replace your OEM slider rails with a beefier set that drops the seat 33–48mm (1.3–1.9”) in 5mm steps and still slides fore and aft normally. The whole thing bolts on and comes back off stock. The one thing the product page understates: dropping the cushion reclines you, and you will want to deal with the backrest angle as part of the same job.

This page is the Jass-specific detail. For how Jass stacks up against Paco and Aurora, see lowering the ND seat.

What you actually buy

Section titled “What you actually buy”

Jass sells three ND lowering products plus the backrest kit, and the names blur together:

ProductDropSliderBest for
Lowering rails, standard33–48mm (1.3–1.9”), adjustable in 5mm stepsYes, full travelMost drivers; dial in your own height
Lowering rails, extreme58mm (2.3”)YesVery tall drivers who need the maximum
Fixed adapters56mm (2.2”)No, four preset fore/aft positionsA fixed deep drop; OEM or Recaro seats
Backrest raising kitraises the backrest ~50mmn/aRestoring the recline angle after a deep drop

The standard adjustable rails are the version most ND owners want, and the one Jass’s own decision chart steers most people to. They fit the OEM seat and keep the slider, so you give up nothing day to day. Everything is sold per side, so a driver-only setup is half the cost.

Pick the drop by your height

Section titled “Pick the drop by your height”

The adjustable rails are the point of the standard kit: you bolt the seat to one of the 5mm-spaced positions and can change it later. Jass flags that the deepest settings have a floor on driver size. The 58mm extreme rails and 56mm fixed adapters are aimed at drivers over roughly 191cm (6’3”), because a taller driver carries more of the height in the torso and chest; a shorter driver who slams the seat that low ends up reaching for the wheel and pedals. Start one notch shallower than you think and drop further only if you still clear the roof with margin.

What that buys in practice: an ND owner who fit the standard rails measured about 2cm of fresh headroom and called the kit “really well-thought-out,” with keeping the slider function “huge.”

It keeps the slider, and it reverses

Section titled “It keeps the slider, and it reverses”

This is the Jass differentiator. Because the rails are sliders, a second driver still moves the seat with the normal lever. A 6’ ND owner with a long torso who runs the Jass adjustable brackets put it plainly: the kit “gives me great head room and still allows me to adjust the seat forward and back,” and the seat stays adjustable “for my wife or when I wear different shoes.” The same owner notes the install is expensive but reversible: nothing is cut, so the OEM rails go back on if you sell.

De-tensioning releases the factory springs that hold the seat foam firm

Section titled “De-tensioning releases the factory springs that hold the seat foam firm”

Before you buy rails, Jass documents a stack of free, reversible moves in their ND seat lowering guide, and two of them are “de-tensioning”: one on the seat back, one on the seat base. Physically they do the same thing. The factory holds the foam taut and proud of the frame with sprung tensioners, so you sit up on a firm cushion. Detach them and the foam slackens, so you settle into the seat instead of perching on it. The feel differs front to back, and it’s the part owners ask about most.

  • The backrest tensioner. Factory tension springs stop the seatback from reclining fully. Detach them (Jass rates it easy, about 10 minutes, reversible) and the backrest leans back about 80mm, which Jass puts at roughly 20–25mm (about 1”) of perceived headroom across its pages. You sit deeper between the side bolsters, more reclined, head back and down. One ND owner who lowered on the Jass rails and released the seat-back tension went from scrunching down to passing a hand flat over his head and wearing a ball cap, and described finally sitting “in” the seat instead of “on” it. The trade is support: the seatback gives more and the lumbar feel softens, so long-haul drivers often add a lumbar cushion back. On track it runs the other way, since sitting deeper between the bolsters is more lateral support, not less.
  • The base tensioners. Two tensioners on the underside of the seat frame over-tension the cushion from the factory. Pop them off (a flat screwdriver and a hammer tap, about 5 minutes, reversible) and the seat settles slightly once it’s back in the car. The headroom gain is minimal; what you feel is the cushion going from sprung-firm to softer, hips a few millimeters lower. If the stock seat struck you as hard or perched, this is the closest move here to a pure comfort change.

Lowering reclines you, and the raising kit fixes what tension release can’t

Section titled “Lowering reclines you, and the raising kit fixes what tension release can’t”

Drop the cushion and the backrest angle goes wrong: the backrest pivots from a fixed point that didn’t move down with your hips, so you end up more reclined than the factory geometry intended, with the bolsters, headrest, and belt guides sitting high on your body. Releasing the backrest tension above absorbs some of this for free. When it isn’t enough, the Jass backrest raising kit bolts the backrest up about 50mm to restore the factory relationship after a deep drop, keeps the reclining mechanism, and needs no cutting. Know its limit before buying: it only works from the backrest-parallel-to-the-rear-wall position and further back, so it cannot pull the seatback more upright. A shorter driver who wants to sit forward and tall can find themselves stuck too reclined.

If the seat bottom feels right but the back doesn’t, that’s the recline problem, and the raising kit is the targeted fix rather than re-doing the rails.

Install reality

Section titled “Install reality”

It’s a seat-out job. Pull the seat (four 14mm bolts plus the airbag and occupant-sensor connectors, with the SRS-safe battery disconnect) per seat removal, swap the OEM sliders for the Jass rails, set your drop, and reinstall. Budget one to two hours per side the first time. The consistent owner gripe is access: the bolts behind the seat back are the tight part and the Jass sliders are “quite beefy,” so getting everything to line up in the limited space takes patience, not force. On the deepest settings some seats want minor clearancing to sit flush. Torque the structural seat bolts back to about 28 lb-ft (38 N·m).

How it compares, in one paragraph

Section titled “How it compares, in one paragraph”

Paco is cheaper and lighter (−6.5 lb/seat) but fixed: you loosen bolts to slide. Aurora keeps the slider like Jass but requires cutting the factory base and costs more. Jass is the pick when you want adjustability, full slider function, and a fully reversible install, and it’s the only one that also sells the backrest fix. The trade is sourcing: Jass ships from the EU, so US buyers either pay freight or buy through a reseller like Moss Miata. The full three-way comparison, with prices and owner accounts, is on the seat lowering overview.

Further reading

Section titled “Further reading”