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The TEIN STREET BASIS Z coilover kit, part number GSM74-81SS2, is designed for the 2006-2015 Mazda MX-5 Miata with the 2.0L engine and rear-wheel drive. Featuring threaded spring-seat ride-height adjustment, fixed-damping twin-tube shock absorbers, and 5.5K front / 3.5K rear springs, this suspension kit provides adjustable lowering without the complexity of damping controls. TEIN recommends approximately 1.4 inches of lowering at both ends for U.S.-market NC Miata models.
Key Features & Specifications:
Brand: TEIN
Series: STREET BASIS Z
Product Type: Height-Adjustable Lowering Coilover Suspension Kit
Part Number: GSM74-81SS2
Fitment Years: 2006-2015 (USA)
Make: Mazda
Model: MX-5 Miata
Generation: NC
Chassis: NCEC
Engine: 2.0L 4-Cylinder
Drivetrain: Rear-Wheel Drive (RWD)
Damping Adjustment: No — Fixed Damping Front & Rear
Ride Height Adjustment: Threaded Spring Seats, Front & Rear
Full-Length Ride Height Adjustment: No
Damper Design: Twin-Tube
Front Upper Mounts: Factory OEM Mounts Reused
Rear Upper Mounts: Factory OEM Mounts Reused
Front Spring Rate: 5.5 kgf/mm (308 lbs/in)
Rear Spring Rate: 3.5 kgf/mm (196 lbs/in)
Front Spring Free Length: 225mm
Rear Spring Free Length: 225mm
Front Spring Part Number: S8M74-13055
Rear Spring Part Number: S8M75-13035
Recommended Front Lowering: 1.4in (35mm)
Recommended Rear Lowering: 1.4in (35mm)
EDFC Compatibility: No
Kit Coverage: Front and Rear Suspension
Fitment:
U.S.-Market Mazda MX-5 Miata
2006-2015 Mazda MX-5 Miata 2.0L RWD (NC/NCEC)
Japanese-Market Mazda Roadster
August 2005-May 2015 Mazda Roadster 2.0L RWD (NCEC), Base, RS and VS
Fitment Notes:
Designed for the NC-generation Mazda MX-5/Roadster, not earlier NA/NB or later ND generations.
Japanese-market fitment was not tested by TEIN on vehicles equipped with the power-retractable hardtop.
Original front and rear upper mounts must be reused.
Verify the vehicle's model year, market specification and suspension configuration before ordering.
The TEIN STREET BASIS Z is a straightforward suspension upgrade for NC Miata owners who want a lower stance without spending time adjusting shock firmness. It combines height-adjustable coilovers with fixed-damping twin-tube shock absorbers, making it a practical choice for a street-driven MX-5.
The dampers are designed around everyday driving, while the threaded spring seats allow you to adjust the vehicle's height within TEIN's specified range.
Unlike STREET ADVANCE Z, STREET BASIS Z does not offer damping adjustment. Unlike FLEX Z, it does not use full-length adjustable damper bodies. Instead, it focuses on adjustable lowering with a simpler setup.
Part GSM74-81SS2 fits the third-generation Mazda MX-5 Miata with the 2.0L engine and rear-wheel drive.
The kit uses 5.5 kgf/mm front springs and 3.5 kgf/mm rear springs, matched to TEIN's fixed-damping shock absorbers. Both ends reuse the original upper mounts, so the kit does not include pillowball mounts or adjustable camber plates.
For U.S.-market models, TEIN recommends a starting ride height approximately 1.4 inches lower than factory at both the front and rear.
The kit is well suited to Miata owners who want to reduce wheel gap and choose their ride height without moving to a fully adjustable suspension system.
| Vehicle Application | Front | Rear |
|---|---|---|
| 2006-2015 U.S. MX-5 Miata | -1.4in (-35mm) | -1.4in (-35mm) |
| 2005-2015 Japanese Roadster | -1.4in (-35mm) | -1.2in (-30mm) |
| Vehicle Application | Front | Rear |
|---|---|---|
| U.S. MX-5 Miata | -1.8in to -1.0in | -1.8in to -1.0in |
| Japanese Roadster | -2.2in to -1.4in | -2.0in to -1.2in |
| Vehicle Application | Front | Rear |
|---|---|---|
| U.S. MX-5 Miata | -3.3in to -0.4in | -2.2in to -0.6in |
| Japanese Roadster | -3.6in to -0.6in | -2.2in to -0.6in |
Ride-height measurements are relative to the vehicle's original suspension height. Maximum adjustment limits are not recommended everyday driving settings. Actual lowering depends on vehicle condition, suspension travel and wheel and tire clearance.
| Specification | Front | Rear |
|---|---|---|
| Spring Rate | 5.5 kgf/mm | 3.5 kgf/mm |
| Spring Rate (lbs/in) | 308 | 196 |
| Free Length | 225mm | 225mm |
| Spring Part Number | S8M74-13055 | S8M75-13035 |
Upper Mounts: Reuse factory OEM upper mounts front and rear.
Damping: Fixed at both ends; no damping adjustment is provided.
Ride Height: Adjustable through threaded spring seats, not damper-body length.
EDFC: Not compatible with TEIN electronic damping controllers.
Power-Retractable Hardtop: TEIN's Japanese Roadster application was not tested with this roof configuration; confirm compatibility before ordering for that application.
Installation: Professional suspension installation and a complete wheel alignment are recommended after fitting or adjusting the coilovers.
For NC Miata owners looking for adjustable lowering without extra damping controls, TEIN STREET BASIS Z offers a straightforward suspension setup with model-specific spring rates and recommended ride heights.
