Mini-Z Pinion Gear Ratios: 6T-9T for MR-03 and MR-04

Gear ratio is one of those tuning variables that gets less attention than it deserves in Mini-Z circles. People obsess over tire compound and spring rate, then run whatever pinion gear came in the car and wonder why it feels slightly off at the top end, or why the motor runs warm after a session on RCP.

The pinion size you run changes the mechanical gear ratio between your motor and your rear spur gear. That determines how fast your motor spins relative to the wheels, and therefore how the car feels at different points in the throttle range. It also determines how hard your motor works, which directly affects heat and battery consumption.

This guide gives you the reference table first, then a short explanation of how to read it and when to change your pinion.

How Mini-Z Gearing Works

The MR-03 and MR-04 use a fixed spur gear on the rear axle. The motor drives a pinion gear that meshes with the spur. Gear ratio is calculated as:

Gear Ratio = Spur Teeth / Pinion Teeth

Larger pinion = lower numerical ratio = more top speed, harder on the motor. Smaller pinion = higher numerical ratio = more torque, better acceleration, cooler motor.

The stock spur gear on every MR-03 and MR-04 variant is 44T. Kyosho states it directly in its own gear blog, and the ratios on its spec pages (7.3, 6.3, 5.5, 4.9:1) are 44 divided by 6, 7, 8 and 9. Some aftermarket setups run different spur sizes, but for this reference table, 44T is the baseline. The MA-020 and FWD cars use a different gear train, covered in the platform notes below.

On brushed motors, a stock N10 motor draws heat quickly if you’re overdriving it with too large a pinion. On brushless, the KV rating of your motor interacts with the pinion. A 10,000 KV motor on a 9T pinion is a different animal than the same motor on a 6T.

Kyosho Aluminum Pinion Gear Set AWD (MDW021), check price on Amazon

For broader pinion selection beyond the Kyosho aluminum set, search Mini-Z pinion gears on Amazon. Kyosho’s own RWD pinions run 6T-9T, and you’ll find those there or through direct vendors like RCMart and Atomic.

Mini-Z Pinion Gear Ratio Reference Table

The table below assumes a 44T spur gear, which is standard across every MR-03 and MR-04 variant. It does not apply to the MA-020 or MX-01, which have their own gearing (see the platform notes below). Gear ratio listed is the final mechanical ratio (spur/pinion), and it matches the ratios Kyosho prints on its MR-03 and MR-04 spec pages.

Pinion	Ratio (44T spur)	MR-03	MR-04	Best Use Case
6T	7.33:1	Stock brushed, beginner	Stock brushed, beginner	Maximum torque, minimum speed. The pinion that ships fitted on the RWD cars.
7T	6.29:1	Stock class, RCP	Stock class, RCP	Standard starting point for brushed stock racing on MR-03 and MR-04. Good for RCP carpet.
8T	5.50:1	Brushed mod class, brushless low-KV	Brushed mod class	On MR-03, works well with brushless under 10,000 KV. Good all-round pick for RCP.
9T	4.89:1	Brushless mid-KV, carpet	Brushless, fast carpet	Brushless territory on RWD platforms. Good for smooth indoor carpet tracks with consistent surfaces. The largest pinion Kyosho makes for RWD.

What about 10T and 11T? Kyosho makes no RWD pinion above 9T, and the MR-03 manual only shows motor guide positions for 6T through 9T. I haven’t verified that any aftermarket 10T or 11T pinion fits an RWD motor mount, so I’m not listing ratios for them here. The formula above still works if you find one, but check the vendor’s stated fitment first.

Reading the Table

A 7T pinion at 6.29:1 means your spur gear rotates once for every 6.29 motor revolutions. Higher ratio = motor spins more relative to wheel speed = more torque, more heat, lower top speed. Lower ratio (bigger pinion) = motor spins fewer times per wheel revolution = higher top speed, more motor demand.

For RCP track racing (the most common Mini-Z competitive context) 7T or 8T is where most setups live on stock and mod brushed classes. Brushless setups typically start at 8T-9T, the top of what Kyosho makes, and go from there based on the motor’s KV rating and the track layout.

Platform-Specific Notes

MR-03: The MR-03 is the most widely raced Mini-Z platform. For RCP club racing in stock brushed class, 7T is the default. Once you move to brushless via the Brushless Conversion guide, 8T-9T covers most RCP layouts. On outdoor or larger tracks, stay at the 9T end of the range and watch motor heat.

MR-04: The MR-04’s narrower chassis and lighter feel means it responds well to the same pinion range as the MR-03. However, because the car already rotates aggressively, a larger pinion that increases top speed can make it harder to drive on tight tracks, adding another variable to manage. Start conservative (6T-8T) and work up. For more on the MR-04 setup philosophy, see the MR-04 Platform Guide.

MA-020: The AWD cars do not use the 6T-9T pinion and 44T spur setup at all, so the table above does not apply. Kyosho’s MA-020 (and FWD) kits use 15T, 17T, 19T or 21T pinions with a 27T, 29T or 31T spur chosen by wheelbase, plus an internal reduction stage. Kyosho publishes the resulting ratios on its MA-020 spec pages as 7.23, 6.38, 6.0, 5.71, 5.34, 4.97 and 4.5:1. I haven’t derived the internal stage, so read your ratio from Kyosho’s list rather than dividing spur by pinion. The Aluminum Pinion Gear Set AWD (MDW021) linked above is the AWD pinion set. The general rule still holds: AWD has more internal friction than RWD, so a larger pinion loads the motor harder and a smaller one keeps temps down. See the MA-020 Platform Guide for drivetrain context.

MX-01: The MX-01 is a crawler/off-road platform and operates in a different gear ratio world. I haven’t verified its pinion or spur sizes against Kyosho’s published specs, so there are no MX-01 numbers in this guide, and the table above is not a reference for it. See the MX-01 Crawler Guide for platform-specific tuning.

Why Gear Ratio Matters More Than People Think

On a Mini-Z, the motor and ESC are running at high RPM in a small enclosed body. Heat buildup is real and it degrades motor brushes, affects ESC behavior, and shortens battery runtime.

Running a pinion that’s too large for your motor and track combination means:

• The motor spins harder on every straightaway
• ESC current draw increases
• Battery depletes faster
• Motor runs hot, which affects consistency over a 5-minute run

Running a pinion that’s too small means:

• You leave top speed on the table
• The car can feel sluggish on longer straights
• On a tight track, it doesn’t matter much. On an open layout, it costs time.

The right pinion is the one where your motor runs warm but not hot after a full session, and the car feels responsive without needing to spin the wheels to accelerate. If you’re burning through brushes or running the car slower than the competition on the same motor, check your pinion before anything else.

Beginners typically run whatever ships with the car (Kyosho fits a 6T pinion on the RWD cars) and don’t touch it. Fast drivers adjust pinion based on the track layout. A tight technical track with short straights gets a smaller pinion than an open layout with long runs. That set-it-once habit is exactly what most club racers get wrong about gearing: it’s one of the few tuning variables that costs nothing to change and almost nobody revisits after build day.

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One thing to do every single time you swap a pinion: reset the gear mesh. A new pinion has a different outside diameter, so the mesh you had dialed in on the old one is wrong the moment the new one goes on, and running a too-tight mesh is the fastest way to cook a motor or strip a spur. The Gear Mesh guide covers how to set it and what too tight and too loose sound like before you take anything apart.

For motor upgrade context that directly affects pinion selection, see the MA-020 Motor Upgrade Guide for AWD-specific guidance and the Brushless Conversion guide for RWD platform brushless builds. Pinion selection is Tier 1 in the full build order; see the Mini-Z Upgrades guide for context. Browse the full motor and pinion lineup on the Shop Motors page. This is one of several chart-format reference guides on the site if you want the numbers without the narrative.

MiniZ Modder