Sheldon Brown Gear Calculator
Calculate Gain Ratios, Gear Inches, and speed for any bicycle configuration using the legendary Sheldon Brown method.
Select your tire circumference for accurate distance and speed math.
Standard lengths are 165mm, 170mm, 172.5mm, or 175mm.
The number of teeth on the front sprocket being used.
The number of teeth on the rear cassette cog being used.
Current Gain Ratio
6.12
79.5
6.34m
34.2 km/h
Figure 1: Comparison of Gear Inches across typical cassette range (11t to 32t) for the selected chainring.
| Rear Cog (t) | Gain Ratio | Gear Inches | Meters Dev. | Speed (90 RPM) |
|---|
What is the Sheldon Brown Gear Calculator?
The Sheldon Brown Gear Calculator is the gold standard for cyclists looking to understand the mechanical advantage of their drivetrain. Developed by the legendary Sheldon Brown, this method moves beyond simple gear ratios to provide a more comprehensive metric known as the “Gain Ratio.”
Who should use it? Road cyclists, mountain bikers, fixed-gear enthusiasts, and bicycle mechanics use the Sheldon Brown Gear Calculator to compare different gearing setups accurately. A common misconception is that gear inches alone tell the whole story; however, the Sheldon Brown Gear Calculator accounts for crank length, which significantly affects how a gear actually feels to the rider.
By using the Sheldon Brown Gear Calculator, you can determine if a new cassette or chainring will give you the climbing gears you need or the top-end speed you desire. It is a vital tool for bike building and performance tuning.
Sheldon Brown Gear Calculator Formula and Mathematical Explanation
The brilliance of the Sheldon Brown Gear Calculator lies in its “Gain Ratio” formula. Unlike other metrics, Gain Ratio is dimensionless, meaning it compares the distance the pedal moves to the distance the bicycle travels.
The fundamental formula used in the Sheldon Brown Gear Calculator is:
Gain Ratio = (Wheel Radius / Crank Length) × (Chainring Teeth / Cog Teeth)
Variable Definition Table
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Wheel Radius | Total radius including the inflated tire | mm | 310mm – 370mm |
| Crank Length | Distance from center of BB to pedal spindle | mm | 160mm – 180mm |
| Chainring | Front sprocket tooth count | Teeth | 22t – 60t |
| Cog | Rear sprocket tooth count | Teeth | 9t – 52t |
Practical Examples (Real-World Use Cases)
Example 1: The Modern Road Bike
Consider a standard road bike using the Sheldon Brown Gear Calculator. With a 50t chainring, a 17t cog, 172.5mm cranks, and 700x25c tires, the Sheldon Brown Gear Calculator yields a Gain Ratio of approximately 6.03. This means for every inch the pedal moves, the bike moves 6.03 inches forward.
Example 2: The Touring Climber
A touring cyclist carrying heavy bags might use the Sheldon Brown Gear Calculator to find a “granny gear.” With a 24t chainring, a 34t cog, and 170mm cranks, the Sheldon Brown Gear Calculator shows a Gain Ratio of 1.48, allowing for easy spinning up steep mountain passes.
How to Use This Sheldon Brown Gear Calculator
Using our Sheldon Brown Gear Calculator is straightforward:
- Select your Wheel/Tire Size: This determines the rolling circumference.
- Enter Crank Length: Crucial for the Sheldon Brown Gear Calculator gain ratio math.
- Input Teeth Counts: Put your front chainring and specific rear cog numbers.
- Review Results: The Sheldon Brown Gear Calculator updates in real-time. Look at the Gain Ratio for a pure mechanical comparison, or Gear Inches if you prefer traditional units.
Key Factors That Affect Sheldon Brown Gear Calculator Results
Several variables impact the output of the Sheldon Brown Gear Calculator:
- Tire Pressure and Width: A wider or more inflated tire increases the effective wheel radius in the Sheldon Brown Gear Calculator.
- Crank Leverage: Longer cranks provide more leverage, reducing the Gain Ratio in the Sheldon Brown Gear Calculator math.
- Drivetrain Efficiency: While the Sheldon Brown Gear Calculator assumes 100% efficiency, friction from a dirty chain can affect real-world feel.
- Cadence (RPM): The Sheldon Brown Gear Calculator helps you find the right gear to maintain your target cadence, usually between 80-100 RPM.
- Terrain Gradient: Steeper hills require lower numbers in the Sheldon Brown Gear Calculator output.
- Rider Weight/Power: Stronger riders can handle higher Gain Ratios produced by the Sheldon Brown Gear Calculator.
Related Tools and Internal Resources
- Bicycle Gear Ratio Calculator – Compare simple tooth ratios between different bikes.
- Cadence Calculator – Determine your optimal pedaling speed based on speed and gearing.
- Skid Patch Calculator – Essential for fixed-gear riders to calculate tire wear.
- Chain Length Calculator – Find the perfect chain length for your new gearing.
- Fixie Gear Calculator – Specialized tool for single-speed and fixed setups.
- MTB Gear Calculator – Optimized for wide-range 1x cassettes and small chainrings.
Frequently Asked Questions (FAQ)
What is a good Gain Ratio?
It depends on the terrain. For road racing, a Sheldon Brown Gear Calculator gain ratio of 6.0 to 9.0 is common. For climbing, values between 1.5 and 3.0 are ideal.
Why does the Sheldon Brown Gear Calculator include crank length?
Because shorter cranks require more force for the same gear ratio. The Sheldon Brown Gear Calculator is the only tool that accounts for this mechanical difference.
Is Gear Inches the same as Gain Ratio?
No. Gear Inches ignores crank length. The Sheldon Brown Gear Calculator uses Gain Ratio to give a more “honest” mechanical advantage value.
Can I use this for Internal Gear Hubs?
Yes, but you must multiply the Sheldon Brown Gear Calculator result by the hub’s internal ratio for that specific gear.
How accurate are the tire sizes?
They are based on standard ETRTO values. For 100% accuracy in the Sheldon Brown Gear Calculator, measure your actual wheel rollout.
What is ‘Meters of Development’?
It is the distance the bike travels for one full revolution of the cranks, calculated here by the Sheldon Brown Gear Calculator.
Does a 1x vs 2x system matter?
The math in the Sheldon Brown Gear Calculator remains the same; you just calculate for one chainring at a time.
Why is Sheldon Brown’s method still used?
The Sheldon Brown Gear Calculator remains popular because it provides a universal way to compare any bike, from a BMX to a Penny Farthing.