Fixed Gear Calculator

Welcome to the ultimate Fixed Gear Calculator! Whether you’re building your first fixie, tweaking your existing setup, or just curious about gear ratios, this tool will help you understand the heart of your ride. Calculate key metrics like gear inches and skid patches to find the perfect setup for your riding style and terrain.

Fixed Gear Setup Calculator

Gear Ratio Data Table

Gear Ratio Breakdown

Component	Teeth	Ratio	Gear Inches	Skid Patches
Chainring	—	—	—	—
Cog	—	—

What is a Fixed Gear Ratio?

A fixed gear ratio refers to the direct relationship between the number of teeth on the front chainring and the rear cog on a bicycle with a fixed-wheel drivetrain. Unlike geared bikes that allow riders to change gears based on terrain or speed, a fixed-gear bicycle has a single, unchanging gear ratio. This means that for every full rotation of the pedals, the rear wheel rotates a specific, fixed number of times. The choice of this ratio profoundly impacts the bike’s acceleration, top speed, and the rider’s ability to skid or maintain control. Understanding and calculating your fixed gear ratio is fundamental for any fixed-gear cyclist seeking optimal performance and enjoyment. This fixed gear calculator helps demystify these relationships.

Who Should Use It:

• New fixed-gear bike builders planning their first setup.
• Experienced riders looking to optimize their current gear ratio for different riding conditions (e.g., hilly vs. flat terrain, commuting vs. track racing).
• Cyclists interested in understanding tire wear patterns (skid patches).
• Anyone curious about the mechanical relationship between their pedals and rear wheel.

Common Misconceptions:

• “Higher gear means faster”: While a higher gear ratio allows for higher potential top speeds, it also requires more effort to accelerate and maintain speed, especially uphill. The “best” gear is situational.
• “Gear ratio is the only factor”: Wheel size, tire pressure, rider fitness, and terrain also significantly influence how a particular gear ratio feels and performs.
• “All skid patches are equal”: While the calculation provides a theoretical number, actual tire wear can be affected by tire compound, riding style, and surface conditions.

Fixed Gear Ratio Formula and Mathematical Explanation

The core of understanding your fixed gear setup lies in a few key formulas. These calculations translate the physical components of your bike into tangible performance metrics.

Gear Ratio

This is the most fundamental calculation, defining the mechanical advantage or disadvantage you have.

Formula:

Gear Ratio = (Chainring Teeth) / (Cog Teeth)

Explanation: This ratio tells you how many times the rear cog (and thus the rear wheel) rotates for every single rotation of the crankset (and thus the pedals).

Gear Inches

Gear Inches provide a standardized way to compare the “size” of a gear on different bikes, regardless of wheel size. It represents the diameter of a wheel that would travel the same distance in one pedal revolution if it were driven directly by the crank.

Formula:

Gear Inches = Gear Ratio * Wheel Diameter (inches)

or

Gear Inches = (Chainring Teeth / Cog Teeth) * Wheel Diameter (inches)

Explanation: A higher Gear Inch value means it takes more effort to get moving, but you’ll cover more ground with each pedal stroke, leading to higher potential speeds. A lower value is easier to pedal but results in slower speeds.

Development (Distance per Revolution)

Development, sometimes called Rollout, is the actual distance the bicycle travels forward for one full revolution of the cranks.

Formula:

Development (meters) = Gear Inches * π (Pi) * 0.0254

Explanation: This metric is useful for understanding your speed potential. For example, if your development is 7 meters, each pedal revolution moves you forward 7 meters.

Skid Patches

Skid patches are crucial for fixed-gear riders who perform skid stops (locking the rear wheel to slow down or stop). The number of skid patches indicates how many distinct points on your rear tire will wear down as you skid. A higher number means more even tire wear.

Formula:

Skid Patches = Cog Teeth / GCD(Chainring Teeth, Cog Teeth)

Where GCD is the Greatest Common Divisor.

Explanation: To calculate the GCD, you find the largest integer that divides both the chainring teeth and cog teeth without leaving a remainder. For example, if Chainring = 46 and Cog = 16, the GCD is 2. Skid Patches = 16 / 2 = 8.

Variables Table

Fixed Gear Variables

Variable	Meaning	Unit	Typical Range
Chainring Teeth	Number of teeth on the front chainring.	Teeth	28 – 60+
Cog Teeth	Number of teeth on the rear cog.	Teeth	12 – 22
Gear Ratio	Ratio of chainring teeth to cog teeth.	Unitless Ratio (e.g., 2.875:1)	1.5 – 4.5
Wheel Diameter	Overall diameter of the wheel including tire.	Inches	20 – 29
Gear Inches	Equivalent wheel diameter for one pedal revolution.	Inches	50 – 110
Development	Distance traveled per pedal revolution.	Meters	3 – 10
Skid Patches	Number of distinct points on the tire that wear during skids.	Count	1 – 16+
Crank Length	Length of the crank arm.	Millimeters (mm)	155 – 175

Practical Examples (Real-World Use Cases)

Example 1: Urban Commuter Setup

Scenario: Sarah is building a fixed-gear bike for daily commuting in a city with moderate hills and flat sections. She prioritizes maneuverability and moderate tire wear.

Inputs:

• Chainring Teeth: 48
• Cog Teeth: 17
• Wheel Diameter: 27.5 inches (typical for 700c with a common tire)
• Crank Length: 170 mm

Calculations:

• Gear Ratio: 48 / 17 = 2.82:1
• Gear Inches: 2.82 * 27.5 = 77.6 inches
• Development: 77.6 * π * 0.0254 ≈ 6.11 meters
• GCD(48, 17) = 1
• Skid Patches: 17 / 1 = 17 patches

Interpretation: This setup provides a good balance. The 77.6 gear inches offer decent acceleration for city riding and can handle moderate inclines without excessive strain. The high number of skid patches (17) suggests very even tire wear, which is great for longevity. This is a very popular and versatile fixed gear ratio choice for urban environments.

Example 2: Track/Crit Racing Setup

Scenario: John is preparing for criterium races and needs a setup that allows for high speeds on the flats and quick acceleration out of corners.

Inputs:

• Chainring Teeth: 52
• Cog Teeth: 15
• Wheel Diameter: 27.5 inches
• Crank Length: 170 mm

Calculations:

• Gear Ratio: 52 / 15 = 3.47:1
• Gear Inches: 3.47 * 27.5 = 95.4 inches
• Development: 95.4 * π * 0.0254 ≈ 7.51 meters
• GCD(52, 15) = 1
• Skid Patches: 15 / 1 = 15 patches

Interpretation: This is a significantly higher gear than the commuter setup. The 95.4 gear inches indicate that it will require substantial force to get up to speed, but once rolling, John can achieve very high speeds with less pedaling. The 15 skid patches are still good, but slightly less than the previous example due to the prime number relationship. This setup is optimized for pure speed and power output, common in track cycling gears.

How to Use This Fixed Gear Calculator

Using the Fixed Gear Calculator is straightforward. Follow these steps to get your essential fixed-gear metrics:

1. Input Your Components: Enter the number of teeth on your front chainring and rear cog into the respective fields.
2. Specify Wheel Size: Input the total diameter of your wheel, including the tire, in inches. A common measurement for a 700c wheel with a standard tire (like 25c or 28c) is around 27.5 inches.
3. Enter Crank Length: Provide your crank arm length in millimeters. While not directly used in the primary ratio, gear inches, or skid patches, it’s a key spec for bike fit and biomechanics.
4. Click ‘Calculate’: Once your values are entered, click the ‘Calculate’ button. The results will update instantly.

How to Read Results:

• Gear Ratio: A ratio like 46:16 (or 2.875:1) shows the mechanical relationship. Higher numbers mean harder to pedal, faster top end.
• Gear Inches: This is your primary performance indicator. Around 70-80 inches is common for urban riding, while 85+ inches is more typical for track racing.
• Development: Useful for understanding speed. More meters per revolution means higher potential speed.
• Skid Patches: Aim for higher numbers (ideally 8+) for balanced tire wear, especially if you perform skid stops frequently.

Decision-Making Guidance:

• For climbing or resistance: Lower gear inches (e.g., 65-75).
• For speed on flats: Higher gear inches (e.g., 80-95+).
• For longevity and even tire wear: Aim for cog/chainring combinations with a higher GCD, resulting in more skid patches. Combinations like 48:16 (GCD 16, 3 patches) or 46:17 (GCD 1, 17 patches) are often preferred over something like 47:16 (GCD 1, 16 patches).
• Use the “Copy Results” button to save or share your calculations.

Key Factors That Affect Fixed Gear Results

While the mathematical formulas provide a clear picture, several real-world factors influence how your chosen fixed gear setup actually performs and feels:

1. Terrain: Riding in a hilly area necessitates a lower gear (lower gear inches) for manageable climbing. Conversely, flat urban environments or velodromes favor higher gears for maintaining speed.
2. Riding Style: Aggressive riders who accelerate frequently or perform many skid stops might prefer a slightly lower gear for easier bursts of speed and control. More casual riders might opt for a higher gear for cruising efficiency.
3. Tire Choice and Pressure: Wider tires generally have a larger overall diameter than narrower ones, effectively increasing your gear inches slightly. Tire pressure also affects the effective diameter and rolling resistance.
4. Chainline: A straight chainline (where the chainring and cog align perfectly perpendicular to the rear hub) is crucial for efficient power transfer and reduced drivetrain wear. An improper chainline, even with the “correct” ratio, can lead to problems. This calculator assumes a perfect chainline.
5. Rider Strength and Fitness: A rider with strong legs and good cardiovascular fitness can handle higher gear inches more comfortably than a beginner or less conditioned rider. What feels “right” is highly subjective.
6. Component Wear: A worn chain or cog can slightly alter the effective ratio and increase noise and inefficiency. Regularly maintaining your drivetrain is important.
7. Wheel Size Variations: While we use a standard wheel diameter input, slight variations exist between different rim and tire combinations. Always measure your actual wheel diameter for the most accurate results.

Frequently Asked Questions (FAQ)

What is the most common fixed gear ratio?

The most common fixed gear ratios for urban riding tend to be around 46:16, 48:17, or 44:16, which typically fall between 75-80 Gear Inches. This offers a good balance for most city conditions.

How do I calculate the GCD for skid patches?

The Greatest Common Divisor (GCD) is the largest number that divides two integers without leaving a remainder. For example, GCD(48, 16) = 16. To calculate skid patches: Cog Teeth / GCD. So, 16 / 16 = 1 skid patch. For 46:17, GCD(46, 17) = 1, so 17 / 1 = 17 skid patches.

Should I use a higher or lower gear ratio?

It depends on your terrain and riding style. Lower gear inches (e.g., 70) are easier to pedal, good for hills and quick acceleration. Higher gear inches (e.g., 85) are harder to start but allow for higher speeds on flats.

What does 46×17 mean?

“46×17” is shorthand notation for a fixed gear setup where the chainring has 46 teeth and the cog has 17 teeth. It implies a Gear Ratio of 46:17.

How does crank length affect my gear ratio?

Crank length does not directly change the gear ratio, gear inches, or skid patches. However, longer cranks can make it feel harder to spin the same gear, while shorter cranks can make it feel easier. It primarily affects leverage and rider biomechanics.

Can I change my gear ratio by changing only the chainring or cog?

Yes. You can adjust your gear ratio by changing either the chainring or the cog. Changing the chainring has a larger impact due to its position in the ratio calculation. For example, adding 2 teeth to the chainring is equivalent to removing roughly 6-7 teeth from the cog for the same ratio change.

What is a “suicidal gear”?

A “suicidal gear” is a term used for an extremely high gear ratio (e.g., 60+ gear inches) that is very difficult to pedal, especially for starting and climbing. It’s often used by very strong riders in specific track racing situations.

How do I choose the right wheel diameter?

Wheel diameter is typically determined by the size of your frame’s wheel mounts (e.g., 700c, 26-inch, 29-inch). The value you input should be the *total* diameter including the tire. Use a tape measure for accuracy. Common values range from 26 inches (for smaller MTB wheels) to 29 inches (for larger MTB wheels or 700c with larger tires).