G2 Gear Calculator: What It Is & How to Use It

A G2 gear calculator works out the correct gear ratio for a two-speed (G2) drivetrain, typically used in bicycles, go-karts, or small machinery. You enter the number of teeth on the front and rear sprockets (or chainrings and cogs), and the calculator returns the gear ratio, gear inches, and speed at a given cadence or RPM. This helps you compare setups, plan for hill climbing or top speed, and avoid buying the wrong parts.

Formula

The core formula for a gear ratio is simple:

Gear Ratio = Front Teeth ÷ Rear Teeth

For example, a 32-tooth front chainring and a 16-tooth rear cog gives a ratio of 2.00. This means the rear wheel turns twice for every full turn of the pedals (or engine crank).

From the ratio, you can derive two other useful numbers:

• Gear inches = Gear Ratio × Wheel Diameter (in inches). This is the equivalent diameter of a direct-drive wheel, a traditional way to compare gearing across different wheel sizes.
• Speed = Gear Ratio × Wheel Circumference × Cadence (or RPM). If you know your pedaling cadence (typically 60–100 RPM), you can estimate your speed. The formula in the calculator uses the wheel diameter you enter, converts it to meters, multiplies by Ï€ to get circumference, then multiplies by cadence and 60 to get meters per hour, then divides by 1000 for km/h.

All units are standard: teeth are unitless, wheel diameter is in inches, cadence is in revolutions per minute, and speed is in km/h. If you prefer miles per hour, multiply the km/h result by 0.621371.

Why Use a G2 Gear Calculator?

A G2 (two-speed) gear calculator is most useful when you are building or modifying a vehicle or bike with two selectable gears. Unlike a multi-speed bike with a derailleur, a two-speed setup often uses an internal hub or a jackshaft with two chainrings. You need to know if your chosen gear combination will give you a reasonable ratio for your intended use.

For example, a mountain biker might want a low gear for steep climbs and a higher gear for flats. A go-kart builder might want a ratio that gives good acceleration without sacrificing top speed. The calculator lets you test different tooth counts before you spend money on parts.

It’s also handy for comparing your current setup to a new one. If you’re thinking of changing the front chainring from 32 to 36 teeth, you can see the effect on gear inches and speed instantly.

How to Choose the Right Gear Ratio

Choosing a gear ratio depends on your goal, terrain, and the power source (human or motor). Here are some general guidelines:

• For climbing: A lower gear ratio (e.g., 1.5 or less) makes it easier to pedal uphill. For a bike, that means a smaller front chainring or a larger rear cog.
• For speed on flat ground: A higher gear ratio (e.g., 2.5 or more) lets you go faster at the same cadence, but it’s harder to accelerate.
• For go-karts: A ratio around 6:1 (engine sprocket to axle sprocket) is common for acceleration, while 4:1 gives more top speed. But this varies with engine power and tire size.
• For a two-speed hub: The internal gears are fixed, so you can’t change the ratio, but you can choose a chainring/cog combo that gives the right overall range.

Always consider the wheel size. A 26-inch wheel with a 2.0 ratio will have a different speed than a 20-inch wheel with the same ratio. That’s why gear inches and speed are more useful than just the ratio alone.

Common Mistakes and Misconceptions

One common mistake is mixing up the front and rear teeth. Always divide front by rear, not the other way. Another is forgetting that wheel diameter is not the same as wheel radius or tire size. Use the actual outer diameter of the tire, not just the rim size. For example, a “26-inch� bike wheel might have an actual diameter of 26.5 inches with a tire, which changes the speed calculation slightly.

Another misconception is that a higher gear ratio always means faster. In reality, you need enough power or torque to turn that gear. A ratio that’s too high will make you stall or strain. That’s why many vehicles have a two-speed gearbox: first gear for torque, second for speed.

Also, be careful with units. If you enter wheel diameter in centimeters but the calculator expects inches, your speed will be off by a factor of 2.54. Always check the unit labels.

Limitations of the Calculator

This calculator gives you the theoretical gear ratio and speed, but it doesn’t account for real-world factors like friction, wind resistance, rider weight, or engine power. The speed is a maximum at that cadence, assuming no slippage and perfect efficiency. In practice, you’ll go slower on hills or into wind.

It also assumes a direct connection between the front and rear sprockets. If you have a jackshaft or an internal hub with its own gear ratio, you need to multiply the external ratio by the internal ratio. For example, if your hub has a 1.5 internal reduction and your sprockets give 2.0, the total ratio is 3.0.

For go-karts, the wheel diameter is the outer diameter of the tire, not the rim. A typical go-kart tire might be 11 inches tall. Enter that, not the rim size.

Alternatives and Related Tools

If you’re working with a multi-speed bike, a gear calculator that handles multiple sprockets is more useful. For internal hub gears, you might use a gear inch calculator that includes the hub’s gear ratios. For motorized vehicles, a speed calculator that uses engine RPM and transmission ratios is more appropriate.

This G2 calculator is specifically for two-speed setups, but the same formula applies to any single gear combination. If you have a single-speed bike, you can use it too—just ignore the “two-speed� aspect.

Frequently Asked Questions

What is a good gear ratio for a go-kart?
A common starting ratio for a go-kart with a 6.5 HP engine is 6:1 (engine sprocket to axle sprocket) for acceleration. For higher top speed, try 4:1. But this depends on the engine’s power band, tire size, and weight. Use the calculator to see what speed each ratio gives at your engine’s peak RPM.

How do I convert gear ratio to gear inches?
Multiply the gear ratio (front teeth ÷ rear teeth) by the wheel diameter in inches. For example, a 32/16 ratio (2.0) on a 26-inch wheel gives 52 gear inches. That number is the equivalent diameter of a penney-farthing front wheel, but it’s just a comparative figure.

Does a higher gear ratio make you go faster?
Not necessarily. A higher ratio (more front teeth or fewer rear teeth) gives a higher speed at the same cadence, but it requires more effort to turn. If you can’t maintain the cadence, you’ll actually go slower. The ideal ratio is one that matches your strength and the terrain.

What is the difference between gear ratio and gear inches?
Gear ratio is just the tooth count division, a unitless number. Gear inches adds wheel size to give a more meaningful comparison. For example, a 2.0 ratio on a 20-inch wheel gives 40 gear inches, while on a 26-inch wheel it gives 52 gear inches. The latter will be faster at the same cadence.

Can I use this calculator for a single-speed bike?
Yes. A single-speed bike is just a two-speed with only one gear. Enter the front and rear teeth, and you’ll get the ratio, gear inches, and speed. The calculator doesn’t care how many gears you have, only the one you enter.

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in t | Front teeth | teeth | 32 | 1
in r | Rear teeth | teeth | 16 | 1
in c | Cadence | RPM | 80 | 1
in w | Wheel diameter | inches | 26 | 1
out ratio | Gear ratio | - | t / r | 2
out inches | Gear inches | inches | (t / r) * w | 1
out speed | Speed | km/h | (t / r) * w * 0.0254 * pi * c * 60 / 1000 | 1