How to Choose the Right Seat Lowering Adapters for the Mazda MX-5 ND
A practical guide to the full Jass Performance range — 33mm to 58mm — and how to match them to your height, proportions, and purpose.
If you've landed here, you need to lower the seat of your MX-5 ND or Fiat 124 Spider. The options run from 33mm to 58mm, with fixed adapters or sliding rails. This guide walks you through the ergonomics and helps you choose — based on why you need to lower, not just how tall you are.
Ergonomics — Why the Seat Doesn't Just Go Straight Down
This matters for choosing correctly, so it's worth a few paragraphs.
Automotive engineers use two reference figures: the Largest Man (LM) — the tallest driver the car must accommodate — and the Smallest Woman (SW) — the shortest. In an MX-5 scenario, fitting a 160cm driver and a 200cm driver in the same car means designing for a 40cm difference in body height, split roughly as 20cm of leg length and 20cm of upper body.
When a car seat is lowered, it doesn't drop parallel to the floor. It pivots around the front. The rear drops significantly more than the front. This creates an increasingly aggressive rake angle as the seat goes lower. The backrest kinematics are also affected — at lower positions, the backrest can recline further forward.
For a short driver (small woman), a higher seat position is comfortable — she can see out and reach the pedals with shorter legs. For a tall driver (large man), the rear of the seat needs to go as low as possible to get the upper body under the roof, while the legs, constrained by the footwell length, need to fold up. The backrest needs to accommodate an upper body that is 20cm longer than the design midpoint.
This is why seat lowering in the ND is not a single product for everyone — the right amount of drop, and the right rake angle, depends on your proportions and what you're trying to achieve.
What Are You Trying to Achieve?
Choose the path that fits your situation:
Path A: More Comfort
Estimated height: 175–189cm
You can fit and drive the ND, but headroom is compromised — especially front and rear visibility through the rear-view mirror. You want a better driving position without going further than necessary.
The 48mm drop on its own may be too aggressive at this height range — it raises the knees too high. The Fine Drop Adjustment Kit allows you to start at 33mm and increase in 5mm steps to find the exact position. Detaching the height adjustment rack at the front of the seat lowers the front by an additional ~15mm, completing the setup.
The case for fixed adapters: If you are the only driver, the fixed adapters have two advantages. First, the front of the seat base drops an additional 20mm compared to the rails version — the rails mechanism raises the front by 20mm as part of how they work, which the fixed adapters do not. This makes a meaningful difference for drivers with shorter legs who need comfortable pedal reach. Second, they are cheaper. The trade-off is no sliding adjustment: your seat stays in one position.
48mm Sliding Rails Fixed Adapters — OEM Fixed Adapters — RecaroPath B: Fit with a Helmet
Estimated height: 175–195cm (upper body no more than ~100cm)
A helmet adds 40–50mm above your head. More importantly, it changes your effective proportions: you become a long-upper-body, short-legged driver. Short legs in this context require less rake — or maximum drop at the front of the seat base — to keep pedal reach comfortable and your helmet below the broomstick line.
The fixed adapters lower the front of the seat base 20mm more than the rails — the rails mechanism raises the front by 20mm as part of how they work. Combined with the optional adjustment kit if needed, they deliver the flat rake that a helmeted driver requires. Best choice for broomstick test clearance.
The 48mm version is the only correct rail choice here. Detaching the height adjustment rack lowers the front further. Detaching the backrest tensioners gains additional headroom and improves side support on track.
Path C: Fit at All
193cm and above (depending on body proportions)
At this height you may struggle to sit upright at all, and road visibility through the rear-view mirror is seriously compromised. Every millimetre of drop counts, and a combination of measures is needed.
Maximum drop. Rails are preferred over fixed adapters here for three reasons: the additional drop available in the rearmost seat position, easier installation, and the adjustability — moving the seat slightly forward from the rearmost position angles the backrest, which provides more diagonal distance to the roof and can actually improve both headroom and road visibility.
You will also benefit from all the measures covered in the Additional Challenges section below. Read that section before deciding on your setup.
58mm Sliding Rails (Extreme) Backrest Raising KitAdditional Challenges — and Solutions — for the Tallest Drivers
For drivers above 193cm, seat lowering is necessary but not sufficient on its own. Below is every challenge and the available solutions, drawn from designing these products and driving an ND at 197cm daily.
Backrest
The factory backrest is a compromise between the smallest woman and the largest man. For a very tall driver that puts it 50–75mm below where it should be — the headrest, side supports, and belt routing are all misaligned. The Backrest Raising Kit corrects this by raising the rear of the seat to restore the intended ergonomics.
Headroom
The numbers
At 196–197cm, with a proportionally long upper body of nearly 100cm, the standard headroom in a soft-top ND is approximately 920mm. At the lowest possible seat position (58mm rails), this increases to approximately 980mm. Even there, a 197cm driver is still short by at least 20mm — and the body is 10–15mm taller in the morning than in the evening, which is noticeable.
What actually works
There is no single solution. The following work in combination:
- Raise the backrest — the side supports move up proportionally, and with the tensioners detached, the upper body can lean deep between them, gaining 20–30mm diagonally.
- De-foam the side supports — for drivers with proportionally wide backs (not heavy, just tall), removing the inner foam allows the body to sit lower between the supports.
- Detach the backrest tensioners — the body now leans back and curves slightly rather than being held upright by the OEM backrest tension. This diagonal position gains approximately 20–30mm of effective headroom. It also improves side support on track.
- Move the seat forward slightly — counterintuitive, but moving the seat three clicks forward angles the backrest and provides more diagonal distance to the roof than the fully rearward position. Road visibility also improves because the head moves slightly rearward relative to the mirror. The stretched position makes the raised backrest ergonomics noticeably more effective.
The seating position that works for a 197cm driver — slightly forward, backrest angled, tensioners detached.
Legroom
For drivers with long legs, the measures above are reversed. The seat can be in the full rearward position, and the legs, bent upward, can be supported with the base height adjustment. The conflict for very tall drivers is that rearmost position reduces headroom — the seat-forward trick above addresses this directly.
Front Visibility
Approximately one third of the normal forward field of view is obstructed at very tall driver heights — a consequence of the low roofline combined with the oversized factory rear-view mirror. Lowering the seat helps partially, but the mirror remains an obstruction even at its highest position.
The practical solutions are a smaller aftermarket mirror, or removing the factory mirror entirely and replacing it with a rear-view camera screen. The latter provides a full, unobstructed forward view.
Rear Visibility
58mm adapters installed, rear-view mirror at its highest position. Rear visibility through the lower windows is limited to approximately 4 metres.
With the seat at its lowest and the mirror at its highest, rear visibility through the lower rear windows covers approximately 4 metres. Tilting the head down is required to see following traffic or road signs. The factory mirror dimensions and mounting position are genuinely inadequate for very tall drivers.
Solution: Rear-view camera with dashboard screen, mirror removed completely.
Pedals
On LHD cars the pedals are manageable. On RHD cars there is a structural problem: the clutch pedal collides with the steering rod each time it is depressed. The pedal is straight rather than swept back, which leaves insufficient room for the toe. At shoe size 46EU (UK 11), there is only one possible foot position — between the steering wheel knee clearance and the pedal travel.
Each measure below helps slightly; none resolves it alone:
- Remove car mats — lowers the foot and moves it further from the steering rod
- Use lower-profile shoes — same effect
- Raise the steering wheel to its highest position — allows the leg to travel upward rather than backward
- A smaller steering wheel may help — not confirmed
This remains an unresolved problem on RHD cars.
All Products in This Range
For full specifications, fitment details, and order options for each product:
48mm Sliding Rails 58mm Sliding Rails (Extreme) Fixed Adapters — OEM Fixed Adapters — Recaro Backrest Raising KitAll measurements are metric. A conversion table is available at thecalculatorsite.com. Questions or feedback — contact us.
