MX5 Gearbox Options: A Comprehensive Guide

The Mazda MX5, known affectionately as the 'Miata' in some markets and the 'Eunos Roadster' in Japan, is a beloved sports car renowned for its agile handling and pure driving experience. A significant part of this experience comes down to its gearbox. Whether you're a proud owner of a Mk1, Mk2, or Mk2.5, understanding the available gearbox options and their nuances is crucial for maintenance, modification, and simply appreciating your car's capabilities. This guide delves into the gearboxes fitted to the iconic Mk1 MX5, exploring the differences between manual and automatic transmissions, and even touching on the feasibility of fitting a more modern six-speed gearbox to an earlier model.

Understanding MX5 Gearbox Generations

Mazda introduced the MX5 in 1989, and over its various iterations, the gearbox has seen its share of evolution. While the core ethos of a driver-focused transmission remained, specific ratios and the number of gears have changed.

The Mk1 MX5 (NA Generation: 1989-1998)

In the United Kingdom, the first generation MX5, often referred to as the Mk1, was exclusively offered with a five-speed manual gearbox or an automatic transmission. It's important to note that any automatic MX5 you encounter from this era in the UK would almost certainly have been an import, as automatic variants were not officially sold through the UK market.

Manual vs. Automatic in the Mk1

The five-speed manual gearbox is the quintessential MX5 transmission. It's known for its crisp, short-throw shifts and direct feel, contributing significantly to the car's 'go-kart like' handling. The automatic option, while less common for enthusiasts, was available, primarily in imported models. It's worth noting that the automatic gearboxes and their respective control units differed between the 1.6 and 1.8 litre engine variants of the Mk1.

The Mk2 MX5 (NB Generation: 1998-2001)

Moving into the Mk2 generation, Mazda continued to offer the five-speed manual as standard for most models. However, a significant development emerged: the Roadster RS, an import model, came equipped with a six-speed gearbox as standard. This marked the introduction of more gear ratios for the MX5 line-up.

The Mk2.5 MX5 (NB Generation Facelift: 2001-2005)

The Mk2.5, the facelifted version of the NB, saw further integration of the six-speed gearbox. The 1.8-litre models were available with either a five-speed or a six-speed transmission. The 1.6-litre models, however, remained exclusively with the five-speed gearbox. Additionally, some special edition UK models, such as the tenth-anniversary editions, were also fitted with the six-speed gearbox. As with the Mk1, any automatic transmissions found in Mk2 and Mk2.5 models in the UK are typically imports from Japan.

The Five-Speed vs. Six-Speed Debate

The introduction of the six-speed gearbox brought about noticeable changes in the driving experience. For those accustomed to the five-speed, the six-speed offers a different, often more engaging, feel. Let's explore the key differences:

Driving Experience Differences

• Lower First Gear: The six-speed gearbox features a significantly lower first gear ratio. This means your engine will rev higher in first gear, providing a more immediate sense of acceleration from a standstill.
• Closer Ratios: The gaps between gears, particularly between second and third, are reduced. This results in a smoother, more seamless power delivery as you accelerate through the gears, keeping the engine in its optimal power band more effectively.
• Refinement: It's worth noting that the six-speed gearbox used in the MX5 was manufactured by Toyota. While robust, some drivers find it slightly less refined in terms of shift feel compared to the Mazda-designed five-speed unit. However, this is often a matter of personal preference.
• Higher Final Drive: The sixth gear in the six-speed box typically has a ratio similar to the fifth gear in the five-speed box. This means that at higher, motorway speeds, the engine will be revving slightly higher. While this might seem counterintuitive for fuel economy, it can also contribute to a more relaxed cruising experience for some.
• Enhanced Fun Factor: Ultimately, many enthusiasts find the six-speed gearbox to be more involving and enjoyable to use, especially on twisty roads where the closer ratios and lower first gear can be fully exploited.

Gearbox Ratio Comparison

To truly understand the differences, examining the actual gear ratios provides valuable insight. All five-speed gearboxes across the Mk1, Mk2, and Mk2.5 models share the same internal gear ratios. However, the final drive ratios (which determine how the engine's power is delivered to the wheels) can differ between models and generations.

Here's a typical comparison of the internal gear ratios:

Note: These are typical internal gear ratios. Final drive ratios can vary and will affect the overall gearing.

Can You Fit a Six-Speed Gearbox to a Mk1 MX5?

This is a question that many Mk1 MX5 owners ponder, especially given the perceived benefits of the six-speed transmission. The good news is, yes, you can fit a six-speed gearbox to a Mk1 MX5. It's considered a highly rewarding modification, particularly for those with a 1.6-litre Mk1, as it transforms the driving experience.

The Conversion Process

The good news for Mk1 owners is that the gearboxes are fundamentally similar, and fitting a six-speed unit doesn't typically require extensive or highly specialised modifications to the car's structure. The process generally involves:

• Sourcing a suitable six-speed gearbox (often from a Mk2 or Mk2.5 MX5, or even a specific import).
• Changing the clutch and flywheel (while not always essential, it's often recommended for longevity and optimal performance).
• Modifying or replacing the plate that sits between the engine and the gearbox.
• Potentially changing the starter motor, although this isn't always a mandatory requirement.
• Adapting the propshaft and driveshafts to suit the different gearbox output flange.
• Modifying or replacing the gear shifter assembly and cables.
• Updating the speedometer drive or sensor if the new gearbox has a different output.
• Some transmission tunnel modifications might be needed for clearance.

It's important to remember that this conversion is not limited to the Mk1; a six-speed gearbox can theoretically be fitted to any MX5 Mk1, Mk2, or Mk2.5 model. However, for the Mk1, it represents a more significant upgrade from its original five-speed setup.

Considerations for Competition

If you participate in motorsport, particularly in certain road-going classes like Speed Hillclimbing in the UK, you must be aware of specific regulations. For instance, fitting a six-speed gearbox may not be permitted in most such classes. Always consult the relevant rulebook, such as the MSA Blue Book, for precise details. If a six-speed is not allowed, you might consider changing the final drive ratio to something like a 4.7, which can provide a competitive advantage in terms of acceleration.

Frequently Asked Questions

Q1: Were all UK Mk1 MX5s manual?

Yes, all MX5s officially sold in the UK during the Mk1 era (1989-1998) were manual. Any automatic Mk1s found in the UK are imports.

Q2: What's the main difference between a five and six-speed gearbox in an MX5?

The six-speed gearbox generally offers a lower first gear, closer ratios between gears, and a slightly higher cruising rev at motorway speeds compared to the five-speed. Many find it more engaging to drive.

Q3: Can I swap my Mk1 five-speed for a six-speed?

Yes, it is possible to fit a six-speed gearbox from a later model (Mk2/Mk2.5) into a Mk1 MX5. It's a popular modification.

Q4: Is the six-speed gearbox better?

This is subjective. The six-speed offers closer ratios and a more engaging feel for many, but the five-speed is also highly regarded for its simplicity and directness. The six-speed was manufactured by Toyota, which some purists note as a difference in feel.

Q5: Will a six-speed conversion affect my car's fuel economy?

Potentially. The lower first gear might lead to slightly higher fuel consumption in urban driving. However, the higher top gear might offer similar or slightly better economy on the motorway, depending on your driving style.

Understanding the gearbox options available for your MX5 is key to maintaining its performance and enjoying its driving dynamics. Whether you're sticking with the original five-speed or considering a six-speed upgrade, each transmission offers a unique way to experience the joy of driving this classic roadster.