SPL Parts SPL RKB ND Rear Knuckle Bushing Kit for 2016-2026 Mazda ND Miata MX-5

Vehicle Fitment

• 2016-2026 Mazda MX-5 Miata Soft Top (ND, 1.5L / 2.0L Skyactiv-G I4, RWD) - All Rear Knuckle Bushing Locations
• 2016-2026 Mazda MX-5 Miata RF / Retractable Fastback (ND, 1.5L / 2.0L Skyactiv-G I4, RWD) - All Rear Knuckle Bushing Locations
• 2017-2020 Fiat 124 Spider (ND Platform, 1.4L MultiAir Turbo I4, RWD) - All Rear Knuckle Bushing Locations

Fitment Notes

• This kit replaces all rubber-injected OEM bushings in the rear knuckle assembly - multiple bushing locations per side. It is not a single bushing or a single pair; it is a complete kit for the full rear knuckle on one vehicle.
• Compatible with all ND Miata trim levels (Sport, Club, Grand Touring, RF) and all Fiat 124 Spider trims (Classica, Lusso, Abarth) - all share the same rear suspension geometry.
• All applicable vehicles are rear-wheel drive only - no AWD variants exist for either the ND Miata or the Fiat 124 Spider.
• The Fiat 124 Spider was produced from 2016-2019 for MY2017-2020. Despite sharing the ND platform and rear knuckle geometry with the Miata, its engine and exterior are unique to Fiat.
• Installation requires pressing out the OEM rubber bushings and pressing in the spherical units. A hydraulic press or bushing press tool is required - this is not a hand-installation kit.

Features

• Replaces all rubber-injected OEM rear knuckle bushings with full spherical bearing units, eliminating the compliance, bind, and deflection inherent to the factory rubber design - which causes camber and toe shifts as the knuckle flexes under cornering, acceleration, and braking loads.
• At the limit, the OEM rubber bushings bind and deflect, causing unwanted changes to rear alignment as the suspension cycles through cornering loads, making it difficult to consistently drive the tires to peak grip. The SPL RKB ND removes this variable entirely.
• Full spherical replacement eliminates the artificial spring rate contribution of the OEM rubber bushings, allowing the rear suspension to respond more directly and predictably to inputs from the tires and shock absorbers.
• Smooth articulation through the full suspension travel range - the spherical bearings allow the knuckle to move without the binding and stick-slip behavior that develops in OEM rubber bushings as they age and harden.
• Significant improvement to rear-end consistency on track - the rear knuckle no longer shifts its geometry position under high lateral load, allowing the alignment set at the shop to remain accurate on the circuit.
• Equally beneficial on a street car used for canyon driving and spirited road use where rear-end predictability and consistency are valued over maximum compliance.
• Designed and manufactured entirely in the USA by SPL Parts' in-house engineering and machining team.

Specifications

• Position: All rear knuckle bushing locations (multiple per side, full kit)
• Replacement Type: Full spherical (monoball) bearings replacing OEM rubber-injected bushings with metal sleeves
• Drivetrain: RWD only (all applicable vehicles)
• Installation: Press-fit into OEM knuckle bore - requires hydraulic or bushing press
• Country of Manufacture: USA
• Part Number: SPL RKB ND

Included Components

• Complete set of spherical bushing assemblies covering all rear knuckle bushing locations for one vehicle (both left and right sides)

Product Description

The SPL Parts SPL RKB ND is a complete rear knuckle spherical bushing kit for the Mazda MX-5 Miata ND (2016-2026, both Soft Top and RF body styles) and the Fiat 124 Spider (2017-2020), which shares the ND's platform and rear suspension architecture. The OEM rear knuckle bushings on these vehicles are rubber-injected units with metal sleeves - a design that provides acceptable compliance for street use but introduces measurable camber and toe shifts as the rubber deflects and binds under the lateral, longitudinal, and vertical loads encountered during performance driving. When pushing the ND to its limits on track or at an autocross event, the OEM bushings bind as the suspension cycles through cornering loads, causing the rear alignment to shift in real time and making it difficult to maintain the car at peak grip consistently.

The SPL RKB ND replaces every OEM rubber-injected bushing in the rear knuckle with full spherical bearing units, eliminating the rubber compliance entirely. The spherical replacements articulate freely without binding, without adding the artificial spring rate contribution that rubber bushings create as they deform under load, and without the stick-slip behavior that develops in aged or heat-cycled OEM rubber. The result is a rear knuckle that holds its geometry position accurately under load - the camber and toe set at alignment stay in place on the track rather than shifting through bushing deflection. At the same time, this eliminates the mushy, indistinct rear-end character that results from compliance stacking through multiple rubber bushing points in the rear suspension.

This kit is appropriate for track day builds, autocross cars, time attack vehicles, and street-driven ND Miatas used for spirited driving where rear suspension consistency is valued over maximum ride comfort. Installation requires pressing out the OEM rubber bushing assemblies and pressing in the spherical replacement units - a hydraulic or bushing press is required; this is not a hand-installation job. The kit covers the complete rear knuckle on one vehicle (both left and right sides, all bushing locations). Designed and manufactured in the USA by SPL Parts.