Crown Wheel & Pinion

Gear Ratio Calculator

Use these free calculators to find the correct gear ratio for your application, estimate engine RPM at highway speed, and determine tire diameter. All tools are designed for automotive and commercial differentials using crown wheel and pinion (ring and pinion) gear sets.

A crown wheel and pinion — also known as a ring and pinion gear set — is the core of any differential assembly. The gear ratio is calculated by dividing the number of teeth on the crown wheel by the number of teeth on the pinion. For example, 41 teeth ÷ 11 teeth = a 3.73:1 ratio, meaning the pinion rotates 3.73 times per single crown wheel revolution.

Getting the ratio right directly affects torque output, fuel economy, towing capacity, and driveability. Use our free calculators below to identify your existing differential gear ratio, estimate engine RPM at highway speed, or find the correct ratio after fitting larger tires.

Crown Wheel & Pinion Gear Ratio Calculator

Enter the tooth count on your crown wheel (ring gear) and pinion gear to instantly calculate the gear ratio. This is the most reliable method to identify an unknown ratio when the tag is missing.

Crown Wheel Teeth (Ring Gear)

Pinion Gear Teeth

Your gear ratio is

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Formula: Gear Ratio = Crown Wheel Teeth ÷ Pinion Teeth
Example: 41 teeth ÷ 11 teeth = 3.73 : 1 — meaning the pinion rotates 3.73 times for every single rotation of the crown wheel.

Tire Diameter Calculator

Start here if you plan to use the RPM calculator. You need to know your actual tire diameter. Enter your metric tire size (e.g. 265/70R17) to calculate the diameter in inches and millimeters. The most accurate method is to physically measure from the ground to the top of the mounted tire.

Tire Width (mm)

Aspect Ratio (%)

Wheel Diameter (inches)

Calculated tire diameter

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Tip: Tires with identical size specifications from different manufacturers may have slightly different actual diameters. Always physically measure the mounted tire for the most accurate result. Note: wheel diameter does not affect gear ratio — only vehicle speed and RPM calculations.

Engine RPM Calculator

Estimate engine RPM at a given road speed based on your crown wheel and pinion gear ratio, tire diameter, and transmission type. Use this to compare different gear ratio options before purchasing.

Speed (MPH)

Gear Ratio

Tire Diameter (inches)

Estimated engine RPM at given speed

Auto (no overdrive)

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Auto (with overdrive)

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Manual (direct)

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5-speed (top gear)

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Recommended highway RPM: 4-cyl 2200–3200 · V6 2000–3200 · V8 1800–2800 · Diesel 1600–2800

Formula: RPM = (MPH × Gear Ratio × 336) ÷ Tire Diameter
Overdrive multiplier ≈ 0.70 · Manual direct ≈ 1.00 · 5-speed top gear ≈ 0.83

Return-to-Stock Ratio Calculator (Tire Upgrade)

When you fit larger tires, the effective gear ratio becomes numerically lower (taller), reducing acceleration and fuel economy. Use this calculator to find the compensating crown wheel and pinion ratio that restores your original driving feel.

Original Tire Diameter (in)

New Tire Diameter (in)

Original Gear Ratio

Need a custom Crown Wheel and pinion set?

As a direct manufacturer, XJX Gears produces custom crown wheel and pinion gear sets to your exact ratio, tooth count, and dimensional specifications. Whether you need a standard replacement or a fully bespoke gear set for a commercial vehicle, heavy-duty truck, or specialist application, we have the engineering capability to deliver.

All gear sets are precision-machined and quality-tested before shipment. We also support OEM and bulk orders with competitive lead times.

Contact our team today to discuss your requirements and request a quote.

Crown Wheel & Pinion

Gear Ratio Calculator

Need a custom Crown Wheel and pinion set?

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