Fixie Gear Calculator

An essential tool to calculate gear ratio, gear inches, and skid patches for your fixed-gear or single-speed bike.

What is a Fixie Gear Calculator?

A fixie gear calculator is an indispensable online tool for fixed-gear and single-speed cyclists to determine the characteristics of their drivetrain setup. By inputting the number of teeth on the front chainring and rear cog, along with wheel size, the calculator computes three critical metrics: Gear Ratio, Gear Inches, and Skid Patches. These values help riders optimize their bike for their specific riding style, terrain, and goals, whether it’s for city commuting, track racing, or freestyle riding. Understanding these numbers is fundamental to controlling the feel of the ride and maximizing the lifespan of components, especially the rear tire. This makes a fixie gear calculator a vital resource for both new and experienced riders.

Fixie Gear Calculator Formulas and Explanation

The magic of the fixie gear calculator lies in a few straightforward formulas that convert component sizes into meaningful performance metrics. Here’s how they work:

• Gear Ratio: This is the most direct comparison of your gearing. It tells you how many times the rear wheel rotates for every single rotation of your pedals. A higher ratio means more speed but harder acceleration.
  
  Formula: Gear Ratio = Chainring Teeth / Cog Teeth
• Gear Inches: This metric provides a standardized number to compare gearing across different bikes and wheel sizes. It represents the equivalent diameter of a wheel on a high-wheel bicycle, giving a more universal sense of how “hard” or “easy” the gear feels.
  
  Formula: Gear Inches = Gear Ratio * Wheel Diameter (in inches)
• Skid Patches: Unique to fixed-gear riding, this number tells you how many distinct points on your rear tire will make contact with the ground when you skid to a stop. More skid patches mean your tire will wear more evenly, saving you money.
  
  Formula: Skid Patches = Cog Teeth / GCD(Chainring Teeth, Cog Teeth) (where GCD is the Greatest Common Divisor)

Variables Table

Variable	Meaning	Unit	Typical Range
Chainring Teeth	The number of teeth on the front gear.	Teeth (T)	42T – 55T
Cog Teeth	The number of teeth on the rear gear.	Teeth (T)	13T – 22T
Wheel Diameter	The diameter of your wheel including the inflated tire.	Inches	25″ – 27.5″

Practical Examples

Let’s see how the fixie gear calculator works with two common scenarios.

Example 1: The All-Rounder (Good Setup)

A very popular setup for city riding that balances speed and acceleration, while being great for tire life.

• Inputs:
  • Chainring: 48T
  • Cog: 17T
  • Wheel Size: 700c (27 inches)
• Results:
  • Gear Ratio: 2.82
  • Gear Inches: 76.2
  • Skid Patches: 17
• Analysis: This is a fantastic setup. The gear inches are in a sweet spot for urban environments, and the 17 skid patches (a prime number cog) ensure your rear tire wears very evenly. This is why the 48/17 combination is so highly recommended.

Example 2: The Tire Shredder (Bad Setup)

This is a common ratio found on many off-the-shelf complete bikes, but it’s terrible for tire longevity if you skid.

• Inputs:
  • Chainring: 48T
  • Cog: 16T
  • Wheel Size: 700c (27 inches)
• Results:
  • Gear Ratio: 3.00
  • Gear Inches: 81.0
  • Skid Patches: 1
• Analysis: While the gear ratio is a nice round 3.0, the calculation reveals a major flaw: only one skid patch. This means every time you skid, you are wearing down the exact same spot on your tire, leading to a rapid flat spot and a ruined tire. A simple switch to a 15T or 17T cog would provide a huge improvement.

How to Use This Fixie Gear Calculator

1. Enter Chainring Teeth: Count the number of teeth on your front chainring and enter it into the first field.
2. Enter Cog Teeth: Count the teeth on your rear cog and enter it into the second field.
3. Select Your Tire Size: Choose the option that best matches your bike’s tire size from the dropdown menu. We’ve included common sizes from road to gravel.
4. Review Your Results: The calculator will instantly update.
   • The Gear Inches are displayed prominently as the primary result.
   • Check the intermediate values for Gear Ratio and, crucially, the number of Skid Patches.
5. Analyze the Table: The “Skid Patch Analysis” table dynamically updates to show you the outcome for different cog sizes with your current chainring, helping you plan your next upgrade.

Key Factors That Affect Your Gearing Choice

Choosing the right numbers for the fixie gear calculator depends on several factors:

• Riding Terrain: Hilly areas demand lower gear inches (around 65-75) for easier climbing. Flat cities allow for higher gear inches (75-85) for higher top speeds.
• Rider Strength & Style: Stronger riders or those who like to “mash” a big gear may prefer a higher ratio. Riders who prefer to “spin” at a higher cadence will want a lower ratio.
• Braking Method: If you rely on skidding to stop or control speed, maximizing skid patches is critical. Aim for a cog with a prime number of teeth (like 13, 17, 19). If you use brakes, this is less of a concern.
• Wheel and Tire Size: As shown in the gear inch formula, a larger wheel/tire combination will increase your final gear inches, making the gear feel harder.
• Crank Arm Length: While not a direct input to the calculator, longer crank arms (e.g., 170mm vs 165mm) provide more leverage, making a high gear ratio feel slightly easier to turn over.
• Desired Goal: Are you building a bike for top speed on a velodrome or a nimble machine for navigating traffic? Your goal dictates whether you prioritize a high gear ratio or a more moderate, flexible setup. Using a cadence calculator can help you see how your gear ratio translates to speed.

Frequently Asked Questions (FAQ)

What is a good gear ratio for a fixie?

A good “all-around” gear ratio for city riding is between 2.7 and 3.0. For beginners, starting around 2.7-2.8 (like 46/17) is often recommended.

Why are skid patches so important?

Skid patches determine how evenly your rear tire wears when you skid. A low number (like 1 or 2) will create bald spots on your tire very quickly, forcing you to replace it often. A high number (like 17) distributes the wear, saving you money and ensuring consistent traction.

What is the difference between gear ratio and gear inches?

Gear ratio is a direct comparison of your chainring and cog. Gear inches is a more universal metric that also factors in your wheel size, making it possible to compare the “feel” of gearing between a road bike and a mountain bike, for example.

How do I find my wheel size?

Your tire’s sidewall will have numbers printed on it. Look for a format like “700c x 25mm” or “26 x 2.1”. Our calculator uses these common sizes, but for a precise measurement, you can consult a bicycle tire size calculator.

Can I use this for a single-speed bike with a freewheel?

Yes! The gear ratio and gear inches calculations are exactly the same. The “skid patch” metric is the only one that doesn’t apply, since you can’t skid with a freewheel.

What is an “ambidextrous” skid patch?

This refers to a rider who can skid with either their left or right foot forward. In some specific gear combinations (where both chainring and cog are odd numbers), this can double the effective number of skid patches. Our calculator shows this value for you.

Does crank length affect my gear ratio?

No. Crank length affects the leverage you have on the pedals, which can make a gear feel easier or harder to push, but it does not change the calculated gear ratio, gear inches, or skid patches.

What’s a good number of skid patches?

More is almost always better. Any number above 10 is good. Prime numbers like 13, 17, and 19 are excellent choices for cogs because they often result in that many skid patches, maximizing tire life.