Sheldon Brown Gear Calculator

Advanced Bicycle Gearing Analysis & Gain Ratio Calculator

Cadence (RPM)	Speed (km/h)	Speed (mph)

Speed calculated based on current Sheldon Brown gear calculator inputs.

What is the Sheldon Brown Gear Calculator?

The sheldon brown gear calculator is the gold standard for cyclists looking to understand the mechanical efficiency of their bicycle’s drivetrain. Unlike basic calculators that only look at tooth counts, the sheldon brown gear calculator integrates wheel size, tire width, and specifically crank length to provide a holistic view of gearing.

Developed by the late Sheldon Brown, a legendary bicycle mechanic and technical authority, this calculator introduced the concept of the Gain Ratio. Who should use it? Everyone from competitive road cyclists optimizing for mountain climbs to commuters looking for a more comfortable cadence should consult a sheldon brown gear calculator.

A common misconception is that gear inches are the only way to measure gearing. While gear inches describe the effective diameter of the driving wheel, the sheldon brown gear calculator’s gain ratio describes the actual leverage between the pedal stroke and the ground, making it independent of measurement units.

Sheldon Brown Gear Calculator Formula and Mathematical Explanation

The core innovation of the sheldon brown gear calculator is the Gain Ratio formula. It accounts for the radius of the wheel and the length of the crank arm to show how many units the bike moves for every unit the pedal moves.

The Gain Ratio Formula:

Gain Ratio = (Wheel Radius / Crank Length) × (Chainring Teeth / Cog Teeth)

Variables used in sheldon brown gear calculator math

Variable	Meaning	Unit	Typical Range
Wheel Radius	Half the total diameter of tire + rim	mm	310mm – 370mm
Crank Length	Distance from center of BB to pedal axis	mm	165mm – 175mm
Chainring	Teeth on the front sprocket	Count	22t – 54t
Cog	Teeth on the rear sprocket	Count	11t – 42t

By using the sheldon brown gear calculator, you are essentially calculating the “mechanical advantage” of your bike. If your Gain Ratio is 5.0, your bike moves 5 inches forward for every 1 inch your foot travels in its circular path.

Practical Examples (Real-World Use Cases)

Example 1: The Modern Road Bike

Consider a road bike using 700x25c tires, 172.5mm cranks, and a “compact” 50-tooth chainring paired with a 15-tooth cog. Inputting these into the sheldon brown gear calculator yields a Gain Ratio of approximately 6.5. This tells the rider that for every inch their foot moves, the bike travels 6.5 inches. This is a standard gear for moderate flats.

Example 2: The Touring/Climbing Setup

A touring cyclist carrying heavy panniers might use a 26-tooth small chainring and a 34-tooth rear cog on 26-inch wheels with 170mm cranks. The sheldon brown gear calculator would show a Gain Ratio of about 1.5. This low ratio allows the rider to climb steep inclines without putting excessive strain on their knees, maintaining a healthy cadence.

How to Use This Sheldon Brown Gear Calculator

Using this tool is straightforward. Follow these steps to get precise results for your specific bicycle configuration:

1. Select Tire Size: Use the dropdown to find your ISO tire size (e.g., 25-622 for 700x25c). This determines the wheel’s circumference.
2. Enter Crank Length: Look on the inside of your pedal arm. Most are 170mm, 172.5mm, or 175mm. This is vital for the sheldon brown gear calculator gain ratio result.
3. Input Front Chainring: Count the teeth on your front sprocket (the one attached to the pedals).
4. Input Rear Cog: Count the teeth on the specific gear you are using on the rear wheel.
5. Analyze Results: The sheldon brown gear calculator will instantly update your Gain Ratio, Gear Inches, and potential speed at various cadences.

Key Factors That Affect Sheldon Brown Gear Calculator Results

• Tire Pressure and Load: While the sheldon brown gear calculator uses nominal tire sizes, actual wheel radius varies slightly based on PSI and the rider’s weight.
• Crank Arm Length: Longer cranks provide more leverage, which lowers the Gain Ratio. Short cranks increase it. This is why the sheldon brown gear calculator is superior to simple ratio tools.
• Drivetrain Efficiency: Cross-chaining (using the large ring and largest cog) can introduce friction, though it doesn’t change the theoretical math of the sheldon brown gear calculator.
• Internal Gear Hubs (IGH): Systems like Rohloff or Shimano Alfine have internal ratios that multiply the external chainring/cog ratio.
• Cadence: Your ability to maintain 90 RPM vs 60 RPM drastically changes the “feel” of a gear, even if the sheldon brown gear calculator output remains static.
• Terrain Gradient: A Gain Ratio of 2.0 might feel perfect on a 2% grade but punishing on a 10% grade.

Frequently Asked Questions (FAQ)

Why should I use Gain Ratio instead of Gear Inches?

Gear inches ignore crank length. Since different bikes have different crank lengths, the sheldon brown gear calculator Gain Ratio is the only truly universal measurement that works across all bike types.

What is a good Gain Ratio for climbing?

Most riders prefer a Gain Ratio below 2.0 for steep climbs. Professional mountain bikers often go as low as 0.8 or 1.0 with modern 1x drivetrains.

Does the calculator work for fixed-gear bikes?

Yes! The sheldon brown gear calculator is perfect for fixies because you only have one ratio to optimize. Finding the perfect “magic ratio” for your local terrain is key.

How accurate is the speed table?

It is mathematically perfect based on the inputs. However, aerodynamic drag and rolling resistance will determine if you have the power to actually reach those speeds.

Can I use this for 29er mountain bikes?

Absolutely. Just select the 29-inch tire size or enter the custom circumference in the sheldon brown gear calculator logic.

Why did Sheldon Brown invent Gain Ratio?

He wanted a system that was unit-less (not inches or meters) and accounted for the leverage differences between a 165mm and 180mm crank arm.

How does tire width affect the result?

A wider tire (e.g., 32c vs 23c) has a taller profile, effectively increasing the wheel diameter. This is accounted for in the sheldon brown gear calculator tire presets.

Is 170mm the standard crank length?

Yes, 170mm is the most common, but taller riders often use 175mm. Changing this value in the sheldon brown gear calculator will show you how leverage changes your effort.