Fixed Gear Ratio Calculator
Your expert tool for finding the perfect fixed gear setup. Analyze gear ratio, gear inches, gain ratio, and skid patches to optimize your ride.
Calculate Your Gearing
Number of teeth on the front sprocket (e.g., 44 to 52).
Number of teeth on the rear sprocket (e.g., 13 to 19).
Select your tire size to accurately calculate gear inches and gain ratio.
Common lengths are 165mm, 170mm, or 172.5mm.
Check if you can skid with either foot forward to see potential double skid patches.
Metrics Comparison Chart
What is a Fixed Gear Ratio?
A fixed gear ratio is the fundamental calculation that defines the character of a single-speed or fixed-gear bicycle. It represents how many times the rear wheel rotates for every single revolution of the pedals. This ratio is determined by the number of teeth on the front chainring and the rear cog. A higher ratio (e.g., 3.0) means the bike travels farther with each pedal stroke, offering higher top speeds but requiring more effort to accelerate and climb hills. A lower ratio (e.g., 2.5) provides quicker acceleration and easier climbing but limits top speed, causing the rider to “spin out” at a lower speed. The perfect fixed gear ratio calculator helps riders balance these factors for their specific needs, whether for city commuting, track racing, or learning tricks.
Fixed Gear Ratio Formulas and Explanation
Understanding the numbers behind your ride is key. This fixed gear ratio calculator uses several core formulas to provide a complete picture of your gearing.
1. Gear Ratio
This is the most direct comparison of your gearing. It’s the core value from which other metrics are derived.
Formula: Gear Ratio = Chainring Teeth / Cog Teeth
2. Gear Inches
Gear inches is a classic measurement that relates your setup to the equivalent diameter of a penny-farthing’s wheel. It provides a standardized way to compare gearing across different wheel sizes. A higher gear inch value means a “harder” gear.
Formula: Gear Inches = Wheel Diameter (in) * Gear Ratio
3. Gain Ratio
Gain Ratio is arguably the most scientific metric as it accounts for wheel size, gear ratio, AND crank arm length. It measures the distance traveled for every one unit of distance the pedal travels in its circle. It provides a true mechanical advantage value, independent of units.
Formula: Gain Ratio = (Wheel Radius / Crank Length) * Gear Ratio
4. Skid Patches
For fixed-gear riders, skidding is a common way to brake. A skid patch is a unique spot on your tire that makes contact with the ground when you lock up the cranks. Having more skid patches distributes wear across the tire, significantly increasing its lifespan. This fixed gear ratio calculator determines the number of patches your setup provides.
Formula: Skid Patches = Cog Teeth / GCD(Chainring Teeth, Cog Teeth) (where GCD is the Greatest Common Divisor). The number may double if you are an ambidextrous skidder and certain conditions are met.
Variables Table
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Chainring Teeth | Number of teeth on the front gear | Teeth (count) | 42 – 55 |
| Cog Teeth | Number of teeth on the rear gear | Teeth (count) | 13 – 21 |
| Wheel Diameter | Total diameter of wheel with inflated tire | Inches | 26″ – 27.5″ |
| Crank Length | Length of the crank arm | Millimeters (mm) | 165 – 175 |
Practical Examples
Example 1: The Urban Commuter
A rider wants a versatile setup for city riding with moderate hills. They are looking for a good balance of speed and acceleration, with good tire life.
- Inputs: Chainring = 48T, Cog = 17T, Tire = 700c x 28mm, Cranks = 170mm
- Results:
- Gear Ratio: 2.82
- Gear Inches: 75.6 inches
- Gain Ratio: 5.6
- Skid Patches: 17
- Analysis: This is a classic, well-balanced setup. The gear ratio is ideal for city terrain, and the 17 skid patches ensure fantastic tire longevity. It’s a great starting point, as discussed in this guide on how to choose a fixie.
Example 2: The Speed Demon
A rider on flat terrain wants to maximize their top speed for training and fast group rides.
- Inputs: Chainring = 52T, Cog = 16T, Tire = 700c x 25mm, Cranks = 165mm
- Results:
- Gear Ratio: 3.25
- Gear Inches: 86.1 inches
- Gain Ratio: 6.6
- Skid Patches: 4
- Analysis: This is a very high gear. The 86.1 gear inches provide immense top-end speed but will be difficult to accelerate from a stop. The low number of skid patches means tires will wear out quickly if the rider skids frequently. This setup is explored further in our bike cadence calculator to see how RPM relates to speed.
How to Use This Fixed Gear Ratio Calculator
- Enter Your Chainring Teeth: Input the number of teeth on your front chainring.
- Enter Your Cog Teeth: Input the number of teeth on your rear cog. Using prime numbers like 17 or 19 often maximizes skid patches.
- Select Your Tire Size: Choose the tire size you use from the dropdown. This is crucial for an accurate gear inch chart calculation.
- Input Crank Arm Length: Enter the length of your crank arms in millimeters for an accurate gain ratio.
- Check Ambidextrous Skidder: If you can skid with both your left and right foot forward, check this box to see your maximum potential skid patches.
- Analyze Your Results: The calculator will instantly update your Gear Ratio, Gear Inches, Gain Ratio, and Skid Patches. Use these metrics to fine-tune your ride.
Key Factors That Affect Fixed Gear Ratio Choice
- Riding Terrain: Hilly areas demand a lower gear ratio (e.g., 2.6-2.8), while flat terrains allow for higher ratios (e.g., 2.8-3.2).
- Rider Fitness and Strength: Stronger riders can handle higher gear inches, while newer riders should start lower to build strength and avoid injury.
- Intended Use: Track racing requires high ratios for pure speed. Trick riding and bike polo benefit from lower ratios for control and acceleration. Urban commuting falls in between.
- Cadence Preference: Do you prefer to spin a high cadence or mash a lower one? A lower ratio facilitates a higher cadence. Our cycling power calculator can help you understand this relationship.
- Skid Patches: If you skid to stop, choosing a chainring/cog combo with many skid patches (like 47/17) is a primary concern for saving money on tires. The concept of skid patch calculator is vital for urban riders.
- Wheel and Tire Size: As shown in the calculator, a larger wheel/tire diameter increases the final gear inches, making the gear feel harder. Check our guide on understanding bike gearing for more.
Frequently Asked Questions (FAQ)
A ratio around 2.7 to 2.8 is excellent for beginners. A 46-tooth chainring with a 17-tooth cog (2.71 ratio) or a 48/17 combo (2.82 ratio) are popular and versatile choices that are easy to start on and offer many skid patches.
Even without skidding, fixed-gear riding involves resisting the pedals to slow down (“skip stops”). These micro-adjustments cause uneven wear. A higher number of skid patches distributes this wear more evenly, prolonging tire life.
Gear inches is a traditional metric that’s easy to understand but doesn’t account for crank length. Gain ratio is a more comprehensive, unitless value that factors in wheel size, gearing, and crank length, representing the true mechanical advantage.
To maximize skid patches, use a cog with a prime number of teeth (like 13, 17, 19) and a chainring that does not share any common factors with it. For example, 48/16 simplifies to 3/1, giving only 1 skid patch. 48/17 cannot be simplified, giving 17 skid patches.
A higher ratio provides a higher potential top speed, but only if the rider is strong enough to turn it over at an effective cadence. If a gear is too high, the rider may struggle to accelerate and maintain speed, resulting in being slower overall.
The calculator uses input fields, allowing you to enter any custom chainring and cog combination you want, making it a fully flexible fixed gear ratio calculator.
Think of it as “bang for your buck.” It tells you how many meters the bike moves forward for every meter your foot travels around the pedal circle. It’s the ultimate equalizer when comparing different bikes. This is a core concept for those wanting to understand gain ratio explained.
Yes! The gear ratio, gear inches, and gain ratio calculations are identical for a single speed freewheel setup. Only the “skid patch” metric is specific to fixed-gear riding. This makes it a great single speed gear ratio tool.