Gear Ratio Calculator for Fixed Gear Bikes
Your expert tool for calculating the perfect fixed gear setup.
Calculate Your Gearing
Your Calculated Results:
Intermediate Values:
Development is the distance traveled for one full pedal revolution.
Common Gearing Comparison
| Chainring / Cog | 15T | 16T | 17T | 18T |
|---|---|---|---|---|
| 46T | 82.8 | 77.6 | 73.0 | 68.9 |
| 48T | 86.4 | 81.0 | 76.2 | 72.0 |
| 49T | 88.2 | 82.7 | 77.8 | 73.5 |
| 52T | 93.6 | 87.8 | 82.6 | 78.0 |
Chart: Gear Inches vs. Cog Size for the selected Chainring.
What is a Fixed Gear Ratio?
A gear ratio calculator for fixed gear bikes is an essential tool for any single-speed or track cyclist. The gear ratio determines how many times the rear wheel rotates for every single rotation of the pedals. This simple number has a profound impact on your riding experience, affecting your acceleration, top speed, and ability to climb hills. Unlike geared bikes, a fixed-gear bicycle has only one drivetrain configuration, making the initial choice of chainring and cog critically important. A higher ratio (e.g., 3.0) is harder to pedal from a standstill but allows for higher top speeds, while a lower ratio (e.g., 2.5) provides quick acceleration but limits how fast you can go before “spinning out.”
This calculator helps you find the sweet spot for your riding style and environment, whether you’re navigating city streets, training on the velodrome, or commuting on flat terrain. Understanding your gearing is the first step to mastering the art of fixed-gear cycling.
The Gear Ratio Formula and Explanation
The core calculations are straightforward but reveal a wealth of information about your bike’s performance. The primary metric is the gear ratio itself, from which other important values are derived.
Primary Formula: Gear Ratio = (Number of Teeth on Front Chainring) / (Number of Teeth on Rear Cog)
For example, a setup with a 48-tooth chainring and a 16-tooth cog results in a gear ratio of 3.0. This means for every one full turn of your pedals, your rear wheel completes three full rotations.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Chainring Teeth (C) | The number of teeth on the large front gear. | Teeth (unitless) | 42 – 55 |
| Cog Teeth (S) | The number of teeth on the small rear gear. | Teeth (unitless) | 13 – 22 |
| Wheel Diameter (D) | The diameter of the rear wheel including the tire. | Inches | 26 – 27.5 |
From this, we calculate other key metrics like Gear Inches ((C / S) * D) and Development, which tell you the distance traveled per pedal stroke. Another critical value for fixed-gear riders is Skid Patches, which is determined by simplifying the C/S fraction to find how many unique wear points are on the tire during a skid stop.
Practical Examples
Example 1: The City Commuter
A rider primarily navigates flat city streets with frequent stops and starts. They prioritize quick acceleration over top speed.
- Inputs: Chainring = 46 teeth, Cog = 17 teeth, Wheel Diameter = 27 inches
- Results:
- Gear Ratio: 2.71
- Gear Inches: 73.1 inches
- Skid Patches: 17 (This is a high number, which is great for tire longevity!)
- Development: 5.8 meters
- Interpretation: This is a versatile and popular ratio. It offers good acceleration from a stoplight and a reasonable top speed for urban environments. The high number of skid patches means tire wear is distributed evenly.
Example 2: The Velodrome Racer
A track cyclist needs a high gear for maintaining speed on the banked oval. Acceleration is less of a concern than high-speed efficiency.
- Inputs: Chainring = 52 teeth, Cog = 15 teeth, Wheel Diameter = 27 inches
- Results:
- Gear Ratio: 3.47
- Gear Inches: 93.6 inches
- Skid Patches: 15
- Development: 7.47 meters
- Interpretation: This is a very “heavy” gear. It would be difficult to ride on hilly terrain or in stop-and-go traffic, but on the track, it allows the rider to achieve very high speeds at a comfortable pedaling cadence.
How to Use This Gear Ratio Calculator
Using this gear ratio calculator for fixed gear bikes is simple. Follow these steps to understand your setup:
- Enter Chainring Teeth: Count the number of teeth on your front chainring and enter it into the first input field.
- Enter Cog Teeth: Count the teeth on your rear cog and enter it into the second field.
- Enter Wheel Diameter: For most 700c road bike tires (like 700x23c, 700x25c, 700x28c), a value of 27 inches is a very close approximation and standard for these calculations. If you have a different wheel size, enter its diameter in inches.
- Review the Results: The calculator will instantly update the Gear Ratio, Gear Inches, Skid Patches, and Development (Rollout).
- Gear Ratio: The fundamental measure of your gearing. Aim for 2.7-3.0 for general use.
- Gear Inches: A classic measurement to compare gearing across different bikes. 70-85 inches is a common range.
- Skid Patches: The higher, the better! A prime number cog (like 13, 17, 19) will always give you the maximum number of skid patches.
- Development: The actual distance in meters you travel with one crank revolution.
Key Factors That Affect Gear Ratio Choice
Choosing the right fixed gear ratio is a balancing act. Here are six key factors to consider:
- Terrain: This is the most important factor. If you live in a hilly area, you’ll need a lower gear ratio (e.g., 2.5-2.7) to make climbing manageable. For flat areas, you can push a much higher ratio (2.8-3.2+).
- Riding Style: Are you a “spinner” who prefers a high cadence, or a “masher” who likes to push a big gear? Your personal preference for pedaling speed will influence your ideal ratio.
- Physical Strength: A stronger rider can handle a higher gear ratio without excessive strain. Don’t be afraid to start with a lower ratio and work your way up as your strength improves.
- Top Speed vs. Acceleration: You must choose one to prioritize. A high ratio gives you a high top speed but sluggish acceleration. A low ratio gives you snappy acceleration but you’ll spin out at lower speeds.
- Skid Patches: If you ride brakeless, maximizing skid patches is crucial for extending the life of your rear tire. Choosing a chainring/cog combination that doesn’t simplify to a low integer is key. Using a skid patch calculator can help optimize this.
- Intended Use: A track bike, a commuter bike, and a fixed-gear freestyle bike will all have vastly different gearing needs. Tailor your ratio to what you’ll be doing most of the time.
Frequently Asked Questions (FAQ)
1. What is a good beginner gear ratio for a fixed gear?
A ratio around 2.7 to 2.8 is an excellent starting point for most new riders on relatively flat terrain. This usually translates to a 46/17 or 48/17 setup. It provides a good balance between being easy enough to start and stop, while still allowing for a decent cruising speed.
2. What are skid patches and why are they important?
Skid patches are the number of unique points on your rear tire that make contact with the ground when you perform a skid stop with your cranks in a fixed position. A higher number of skid patches means the wear from skidding is spread out over more of the tire, dramatically increasing its lifespan. A 48/16 ratio, for example, simplifies to 3/1, giving you only one skid patch, which will destroy a tire quickly. A 47/17 ratio gives you 17 skid patches.
3. What’s the difference between Gear Ratio and Gear Inches?
Gear ratio is a pure ratio of the teeth (e.g., 2.8). Gear inches takes the gear ratio and multiplies it by the wheel diameter to provide a standardized number that represents the “equivalent” size of a penny-farthing wheel. It’s useful for comparing gearing between bikes with different wheel sizes.
4. How does changing my chainring vs. my cog affect the ratio?
Changing your cog has a more dramatic effect on the gear ratio than changing your chainring by the same number of teeth. Adding or removing one tooth from the cog makes a bigger difference than adding or removing one from the chainring.
5. Can I use this calculator for a single-speed bike with a freewheel?
Yes. The Gear Ratio, Gear Inches, and Development calculations are identical for any single-speed bike. The only metric that doesn’t apply is “Skid Patches,” as you cannot skid stop using the pedals on a bike with a freewheel.
6. What is Development or Rollout?
Development (or rollout) is the physical distance the bike travels forward with one complete revolution of the pedals. It’s often measured in meters and is a very tangible way to understand how “fast” a gear is. It’s calculated by multiplying the gear ratio by the wheel’s circumference.
7. Why are prime numbers often recommended for cog teeth?
Cogs with a prime number of teeth (like 13, 17, 19) are popular because they are not a common divisor with most chainring sizes. This makes it much more likely that the gear ratio fraction won’t simplify, maximizing the number of skid patches. For example, any chainring that isn’t a multiple of 17 will result in 17 skid patches when paired with a 17t cog.
8. My calculated gear inches seem high/low, what’s wrong?
Ensure your “Tire Diameter” input is correct. While 27 inches is a standard for 700c, a fatter tire (like a 700x38c) might have a slightly larger diameter, and a very skinny one (700x23c) might be slightly smaller. However, for comparative purposes, using a consistent value like 27 is the most common practice.