Yesterday we looked at gear ratios and how to apply them to fixed gear riding, today we are going to build on that knowledge and start to look at more advanced ways to calculate your gear, and how to apply them across bikes.
Gear Ratio: The Basics
What is Gear Ratio?
The gear ratio is the relationship between the number of teeth on the chainring (front sprocket) and the number of teeth on the rear cog (rear sprocket). It determines how many times the rear wheel rotates for each complete revolution of the pedals.
The formula for calculating gear ratio is:
Gear Ratio = Number of teeth on chainring/Number of teeth on rear cog
How Gear Ratios Apply to Fixed Gear Bikes
Since fixies lack multiple gears, selecting an optimal gear ratio is essential for balancing acceleration, top speed, and climbing ability. A high gear ratio means more speed but requires greater effort to accelerate and climb hills. Conversely, a lower gear ratio makes pedalling easier but limits top-end speed.
Example Calculation:
If you have a 48-tooth chainring and a 16-tooth rear cog, the gear ratio would be: 48/16 = 3.00
This means the rear wheel rotates three times for every complete pedal revolution.
Choosing the Right Gear Ratio for Fixies
The ideal gear ratio depends on factors such as:
- Terrain: Flat urban environments may benefit from higher ratios, while hilly areas require lower ratios for better climbing ability.
- Rider Strength and Experience: Stronger riders can handle higher ratios, while beginners may prefer easier gearing.
- Intended Use: Commuting, track racing, and freestyle riding all demand different gearing preferences.
A commonly recommended gear ratio for urban riders is 2.7 to 3.0, balancing speed with ease of acceleration. For tracklocross I would dip slightly lower, especially if you have to deal with mud.
Gear Inches: A Deeper Insight
What is Gear Inches?
Gear inches provide a more tangible way to understand gearing by considering wheel size. The calculation offers a numerical value that represents how far the bike will travel with one revolution of the pedals, incorporating the effect of wheel diameter. You can also include the tyre diameter for an even better calculation.
The formula for calculating gear inches is:
Gear Inches=Gear Ratio×Wheel Diameter (in inches)
How Gear Inches Apply to Fixed Gear Bikes
Gear inches give a clearer picture of how easy or hard a gear feels to ride. A higher gear inch value indicates a harder gear, requiring more effort to pedal but providing greater speed potential. Lower gear inches result in easier pedalling and better hill-climbing capacity. You can also add your tyre diameter to get a more refined answer as well.
| Tyre Size | Wheel and Tyre Diameter |
| 700 x 23 | 82.52″ |
| 700 x 25 | 82.9″ |
| 700 x 28 | 84.1″ |
| 700 x 30 | 84.5″ |
| 700 x 32 | 84.85″ |
| 700 x 35 | 85.35″ |
| 700 x 38 | 85.8″ |
| 700 x 40 | 86.6″ |
| 700 x 42 | 87.6″ |
| 700 x 44 | 88″ |
| 700 x 45 | 88.2″ |
Example Calculation:
Using our previous example (48-tooth chainring, 16-tooth cog) on a standard 700c wheel (which is approximately 27 inches in diameter):
3.00×27=81 gear inches
This means each pedal revolution moves the bike forward the equivalent of an 81-inch wheel rolling one full turn.
Typical Gear Inch Ranges for Fixies
- Low Gear Inches (50-65): Suitable for steep hills and stop-start city traffic, and tracklocross.
- Medium Gear Inches (66-85): Balanced for flat terrain and moderate inclines.
- High Gear Inches (85+): Best for track racing and high-speed riding on flat roads.
Gain Ratio: A More Accurate Measurement
What is Gain Ratio?
Gain ratio refines gear measurements by considering crank arm length, providing a more accurate assessment of mechanical advantage. This concept offers an improved understanding of the rider’s effort relative to the gearing system.
The formula for calculating gain ratio is:
Gain Ratio = (Number of Teeth on Chainring÷Number of Teeth on Rear Cog)×(Wheel Radius÷Crank Length)
Where:
- Wheel Radius: Half the wheel diameter.
- Crank Length: Measured from the centre of the bottom bracket to the centre of the pedal axle (typically 160mm to 175mm).
How Gain Ratio Applies to Fixed Gear Bikes
Gain ratio provides a direct measurement of how far the bike moves relative to leg movement. Since crank length affects leverage, considering it in calculations can help you choose gearing that suits your leg strength and biomechanics.
Example Calculation:
Using a 48/16 gearing, 700c wheels (27-inch diameter, 13.5-inch radius), and 170mm crank arms (converted to inches: 6.7″):
(48÷16)×(13.5÷6.7)=3.0×2.01=6.03
A gain ratio of 6.03 means that for each unit of crank rotation, the bike moves forward 6.03 times that distance.
Advantages of Gain Ratio Analysis
- More Precise Comparison: Gain ratio provides consistency when comparing bikes with different crank arm lengths.
- Improved Efficiency: Helps fine-tune gearing choices based on individual biomechanics.
- Better Understanding of Effort vs. Output: Ensures riders optimise their cadence and power application.
How to Calculate and Optimise Gearing for a Fixie
Step-by-Step Calculation Process
- Determine Your Components:
- Chainring tooth count
- Rear cog tooth count
- Wheel size
- Crank arm length
- Calculate Gear Ratio: Chainring Teeth÷Cog Teeth
- Calculate Gear Inches: Gear Ratio×Wheel Diameter
- Calculate Gain Ratio: Gear Ratio×Wheel Radius×Crank Length
- Evaluate Your Needs:
- Consider terrain, fitness level, and riding style.
- Adjust gearing if necessary by changing the chainring or rear cog.
Practical Considerations for Fixie Riders
When choosing or adjusting fixie gearing, keep the following practical aspects in mind:
- Cadence: A comfortable cadence (pedal revolutions per minute) is usually around 80-100 RPM for most riders. Selecting gearing that allows you to maintain this cadence is essential for efficiency.
- Skid Patches: Fixed gear riders often perform skids to slow down. The number of skid patches (spots on the tyre where wear occurs) is influenced by the gear ratio. Some ratios provide more even wear distribution.
- Component Wear: Lower gear ratios put less strain on the drivetrain, increasing longevity.
- Leg Strength Development: Riding a fixie with a higher gear ratio can build leg strength over time but may strain the knees if not managed carefully.
Understanding gear ratios, gear inches, and gain ratios is fundamental to mastering fixed gear riding. These measurements provide insights into performance, comfort, and efficiency, helping you select the most suitable gearing for your riding style and terrain. Whether you’re commuting, training, or riding for fun, applying these concepts will ensure a smoother and more enjoyable fixie experience.
By learning to calculate and interpret these values, you can make informed decisions about your setups, allowing for a fine-tuned riding experience that balances speed, control, and endurance.
Fiefdom Tracklocross 
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