Sheldon Brown Gear Inch Calculator

Calculate Your Gear Inches

Gear Inch Table

Cog	50T	34T

Gear inches for different cogs with specified chainrings and wheel diameter.

What is the Sheldon Brown Gear Inch Calculator?

The Sheldon Brown Gear Inch Calculator is a tool used by cyclists to determine the “gear inches” of their bicycle’s drivetrain setup. Gear inches represent a relative measure of how hard it is to pedal the bike in a particular gear and how far the bike travels with one revolution of the cranks. It combines the wheel diameter (including tire), the number of teeth on the front chainring, and the number of teeth on the rear cog into a single number. The term and its popularization are closely associated with the late Sheldon Brown, a highly respected bicycle mechanic and technical guru.

Anyone who rides a bicycle, from casual riders to serious racers, can benefit from understanding and using a Sheldon Brown Gear Inch Calculator. It helps in:

• Comparing gearing between different bikes.
• Choosing appropriate gearing for different types of riding (e.g., flat roads, steep hills, time trials).
• Understanding the gear range of a bicycle.
• Selecting new components like cassettes or chainrings.

A common misconception is that higher gear inches are always better. While higher gear inches mean more distance per pedal stroke (and potentially higher speed), they also require more force to pedal, making them harder on hills or when accelerating. A good setup offers a range of gear inches suitable for the rider and terrain.

Sheldon Brown Gear Inch Formula and Mathematical Explanation

The formula to calculate gear inches is quite straightforward:

Gear Inches = (Wheel Diameter in inches) × (Number of Teeth on Front Chainring / Number of Teeth on Rear Cog)

Step-by-step:

1. Determine the Wheel Diameter in inches: This is the effective diameter of the wheel including the inflated tire. While you can measure it, it’s often more practical to use the Bead Seat Diameter (BSD) in mm (e.g., 622mm for 700c, 559mm for 26″ mountain bike wheels) and the tire size to get a more accurate effective diameter, or use a standard value for a given tire size (e.g., 27 inches for a 700c wheel with a 23-25mm tire is a common approximation, though the actual diameter is closer to 622mm + 2*tire width). Our calculator allows mm input and converts using 25.4 mm/inch if you input BSD, or you can directly input an estimated diameter in inches.
2. Calculate the Gear Ratio: Divide the number of teeth on the front chainring by the number of teeth on the rear cog. This gives you the ratio of how many times the rear wheel turns for every one turn of the cranks.
3. Multiply: Multiply the wheel diameter in inches by the gear ratio. The result is the gear inches.

Another related value is “Development” or “Rollout”, which is the distance the bicycle travels in one crank revolution:

Development (meters) = Gear Inches × 0.0254 × π (where 0.0254 converts inches to meters, and π is approximately 3.14159)

Variable	Meaning	Unit	Typical Range
Wheel Diameter	Effective diameter of the wheel + tire	inches or mm	20-29 inches / 406-622+ mm
Chainring Teeth	Number of teeth on the front sprocket	–	22 – 56
Cog Teeth	Number of teeth on the rear sprocket	–	9 – 52
Gear Inches	Calculated gear size	inches	20 – 130
Development	Distance per crank revolution	meters	1.5 – 10

Practical Examples (Real-World Use Cases)

Example 1: Road Bike for Flat Terrain
A cyclist has a road bike with 700c wheels (BSD 622mm), a 50-tooth chainring, and is using a 15-tooth cog. Let’s assume the tire makes the effective diameter around 670mm (approx 26.4 inches).

• Wheel Diameter = 670 mm / 25.4 = 26.38 inches
• Chainring = 50
• Cog = 15
• Gear Inches = 26.38 * (50 / 15) = 26.38 * 3.333 = 87.9 gear inches
• Development = 87.9 * 0.0254 * 3.14159 = 7.0 meters

This is a reasonably high gear, suitable for good speed on flat or slightly downhill sections. Our Sheldon Brown Gear Inch Calculator provides this instantly.

Example 2: Mountain Bike for Steep Climbs
A mountain biker has a bike with 29-inch wheels (BSD 622mm, but larger tires, let’s say effective diameter ~740mm or 29.1 inches), a small 28-tooth chainring, and a large 46-tooth cog for climbing.

• Wheel Diameter = 740 mm / 25.4 = 29.13 inches
• Chainring = 28
• Cog = 46
• Gear Inches = 29.13 * (28 / 46) = 29.13 * 0.6087 = 17.7 gear inches
• Development = 17.7 * 0.0254 * 3.14159 = 1.4 meters

This very low gear inch value allows the rider to spin the pedals more easily up very steep inclines. The Sheldon Brown Gear Inch Calculator helps visualize this low gearing.

How to Use This Sheldon Brown Gear Inch Calculator

1. Enter Wheel Diameter: Input the Bead Seat Diameter (BSD) of your wheel in millimeters (e.g., 622 for 700c, 584 for 650b, 559 for 26″) and select “mm”, or estimate the outer diameter including the tire and enter it with “inches” selected. The tire significantly adds to the BSD to give the effective diameter. For 700c with 25mm tires, 622 + 2*25 = 672mm is more accurate than just 622mm for the rolling diameter.
2. Enter Chainring Teeth: Input the number of teeth on your front chainring.
3. Enter Cog Teeth: Input the number of teeth on your rear cog.
4. View Results: The calculator instantly displays the Gear Inches, Gear Ratio, Development (meters), and potential speed at 90 RPM cadence.
5. Use the Table and Chart: Enter your typical chainrings and cog range to see a table and chart of gear inches across your cassette, helping you understand your gear range and jumps between gears with the Sheldon Brown Gear Inch Calculator.
6. Reset and Copy: Use the “Reset” button to go back to default values or “Copy Results” to save the information.

The results help you understand how “hard” or “easy” a gear will feel and how fast you might go at a given cadence.

Key Factors That Affect Sheldon Brown Gear Inch Results

• Wheel and Tire Size: The most significant factor after the gears themselves. A larger effective wheel diameter (from a larger rim or fatter tire) results in higher gear inches for the same chainring/cog combination. Using the Sheldon Brown Gear Inch Calculator with accurate wheel/tire data is crucial.
• Chainring Teeth Count: More teeth on the chainring lead to higher gear inches (harder gear, more distance per revolution).
• Cog Teeth Count: More teeth on the cog lead to lower gear inches (easier gear, less distance per revolution).
• Number of Chainrings: Bikes with multiple chainrings (e.g., 2 or 3) offer a wider range of gear inches compared to single-chainring setups.
• Cassette Range: The range of teeth on the rear cassette (e.g., 11-28T vs 11-34T) determines the total gear range available and the size of the steps between gears.
• Rider’s Power and Cadence: While not affecting the gear inches number, the rider’s ability to push a certain gear at a comfortable cadence (pedal RPM) determines which gear inches are practically usable.
• Terrain: Hilly terrain necessitates lower gear inches (easier gears) than flat terrain. The Sheldon Brown Gear Inch Calculator helps select appropriate ranges.

Frequently Asked Questions (FAQ)

What are “gear inches”?

Gear inches are a way to measure and compare bicycle gearing, representing the effective diameter of a wheel driven directly by the pedals (like an old Penny-farthing) that would travel the same distance per crank revolution. Higher numbers mean harder gears.

How do I find my wheel’s BSD?

It’s often marked on the rim or in your bike’s specifications. Common BSDs are 622mm (700c/29″), 584mm (650b/27.5″), 559mm (26″). Remember to account for tire height for true effective diameter when using the Sheldon Brown Gear Inch Calculator.

What is “development” or “rollout”?

Development (or rollout) is the actual distance the bike travels forward with one full revolution of the cranks in a given gear. It’s directly related to gear inches.

Is a higher gear inch number better?

Not necessarily. Higher gear inches mean more speed potential at a given cadence but require more force. The “best” gear inches depend on the terrain, rider strength, and desired cadence.

How does tire size affect gear inches?

Fatter tires increase the wheel’s effective diameter, thus increasing gear inches for the same cogs and chainrings. The Sheldon Brown Gear Inch Calculator is more accurate if you consider tire size.

What’s a good gear inch range for climbing?

For steep climbs, gear inches below 30, even below 20 for very steep off-road climbs, are often desirable. Road cyclists might consider under 35-40 as good climbing gears.

What’s a good gear inch range for flat roads?

For flat roads, riders might use gear inches from 60 to over 100, depending on speed and cadence.

Can I use this calculator for any bike?

Yes, the Sheldon Brown Gear Inch Calculator works for road bikes, mountain bikes, hybrid bikes, etc., as long as you know the wheel diameter and teeth counts.