Fixed Gear Ratio Calculator
Calculate your fixed gear bicycle's ratio for optimal performance and skid control.
Complete Guide to Fixed Gear Ratios and Setup Optimization
Choosing the right fixed gear ratio is crucial for performance, control, and riding comfort. This comprehensive guide covers everything you need to know about fixed gear ratios, skid patches, and optimal setup for different riding conditions.
Understanding Fixed Gear Ratios
The fixed gear ratio is the relationship between your chainring and cog teeth, which determines how far your bike travels with each pedal stroke. It's expressed as:
Gear Ratio = Chainring Teeth ÷ Cog Teeth
This simple calculation has significant implications for your riding experience.
Fixed Gear Ratio Ranges by Riding Style
| Riding Style | Typical Ratio | Chainring:Cog | Gear Inches | Cadence at 20mph |
|---|---|---|---|---|
| Street/Urban | 2.7-3.0 | 48:16 to 49:17 | 70-80" | 85-95 RPM |
| Track Racing | 3.3-4.0 | 50:15 to 52:13 | 90-110" | 65-80 RPM |
| Messenger | 2.5-2.9 | 46:18 to 48:17 | 65-75" | 90-100 RPM |
| Fitness | 2.8-3.2 | 47:16 to 51:16 | 75-85" | 80-90 RPM |
Skid Patch Calculation and Importance
Skid patches are the number of different positions your rear tire can skid without wearing out one spot. The formula is:
Skid Patches = Cog Teeth ÷ GCD(Chainring Teeth, Cog Teeth)
Where GCD is the Greatest Common Divisor. More skid patches mean more even tire wear.
| Chainring:Cog | Ratio | Skid Patches | Tire Wear | Common Use |
|---|---|---|---|---|
| 48:16 | 3.0 | 1 | Poor | Track |
| 49:17 | 2.88 | 17 | Excellent | Street |
| 46:18 | 2.56 | 9 | Good | Messenger |
| 47:17 | 2.76 | 17 | Excellent | All-around |
| 51:15 | 3.4 | 5 | Fair | Velodrome |
Gear Inches for Fixed Gear Bikes
Gear inches represent the equivalent diameter of the drive wheel if the bike were direct drive. It's calculated as:
Gear Inches = (Chainring Teeth ÷ Cog Teeth) × Wheel Diameter in Inches
| Gear Inches | Riding Feel | Terrain Suitability | Cadence at 20mph | Example Ratio (700c) |
|---|---|---|---|---|
| 60-70" | Very Light | Hilly | 100-110 RPM | 46:18 |
| 70-80" | Light | Rolling | 85-100 RPM | 48:17 |
| 80-90" | Moderate | Mostly Flat | 75-90 RPM | 49:16 |
| 90-100" | Firm | Flat | 65-80 RPM | 51:15 |
| 100-110" | Hard | Velodrome | 55-70 RPM | 53:14 |
Gain Ratio for Fixed Gear Bikes
Gain ratio accounts for crank length to determine mechanical advantage:
Gain Ratio = (Wheel Radius ÷ Crank Length) × (Chainring Teeth ÷ Cog Teeth)
| Gain Ratio | Pedaling Feel | Optimal Cadence | Example Setup |
|---|---|---|---|
| 4.0-4.5 | Very Light | 90-110 RPM | 46:18, 170mm, 700c |
| 4.5-5.0 | Light | 85-100 RPM | 48:17, 170mm, 700c |
| 5.0-5.5 | Moderate | 80-95 RPM | 49:16, 170mm, 700c |
| 5.5-6.0 | Firm | 75-90 RPM | 51:15, 170mm, 700c |
| 6.0+ | Hard | 65-80 RPM | 53:14, 170mm, 700c |
Optimal Fixed Gear Ratios by Terrain
| Terrain | Ideal Ratio | Gear Inches | Chainring:Cog | Notes |
|---|---|---|---|---|
| Hilly (8%+ grades) | 2.5-2.8 | 60-70" | 46:18 to 47:17 | Easy spinning on climbs |
| Rolling Hills | 2.8-3.0 | 70-80" | 48:16 to 49:17 | Balanced for ups and downs |
| Mostly Flat | 3.0-3.3 | 80-90" | 50:16 to 51:15 | Good cruising speed |
| Completely Flat | 3.3-3.7 | 90-105" | 52:15 to 53:14 | High speed maintenance |
| Velodrome | 3.7-4.2 | 105-120" | 54:14 to 55:13 | Maximum speed |
Speed at Cadence Calculation
You can calculate speed at a given cadence using:
Speed (mph) = (Gear Inches × π × Cadence × 60) ÷ 1056
Or in km/h:
Speed (km/h) = (Gear Inches × π × Cadence × 60) ÷ 656
| Gear Inches | 70 RPM | 80 RPM | 90 RPM | 100 RPM |
|---|---|---|---|---|
| 65" | 12.7 mph | 14.5 mph | 16.3 mph | 18.1 mph |
| 75" | 14.7 mph | 16.8 mph | 18.9 mph | 21.0 mph |
| 85" | 16.6 mph | 19.0 mph | 21.4 mph | 23.8 mph |
| 95" | 18.6 mph | 21.3 mph | 23.9 mph | 26.6 mph |
| 105" | 20.6 mph | 23.5 mph | 26.4 mph | 29.4 mph |
Frequently Asked Questions About Fixed Gear Ratios
General Questions
What is the best all-around fixed gear ratio?
The most versatile fixed gear ratios are:
- 48:17 (2.82 ratio, ~76 gear inches): Excellent skid patches, good for varied terrain
- 49:17 (2.88 ratio, ~78 gear inches): Similar to above with more skid patches
- 46:17 (2.71 ratio, ~73 gear inches): Slightly easier for hills
These provide a balance between acceleration, top speed, and hill climbing.
How do I choose between ratio and skid patches?
Consider these factors:
| Priority | Choose | Example | Notes |
|---|---|---|---|
| Even tire wear | Max skid patches | 47:17 (17 patches) | Prime number chainring |
| Specific ratio | Desired gear inches | 48:16 (3.0 ratio) | Fewer skid patches |
| Compromise | Close ratio with good patches | 49:17 (2.88 ratio) | Best of both |
Technical Questions
How does crank length affect fixed gear riding?
Crank length impacts:
- Leverage: Longer cranks provide more torque but less clearance
- Cadence: Shorter cranks allow higher RPM
- Pedal strike: Longer cranks more likely to hit ground when leaning
Common fixed gear crank lengths:
- 165mm: Technical riding, high cadence
- 170mm: Standard for most riders
- 175mm: More leverage for powerful riders
What's the difference between ratio and gear inches?
Key differences:
| Metric | Calculation | Accounts For | Usefulness |
|---|---|---|---|
| Ratio | Chainring ÷ Cog | Drivetrain only | Comparing setups with same wheel size |
| Gear Inches | (Chainring ÷ Cog) × Wheel Diameter | Wheel size | Comparing different wheel sizes |
Practical Questions
How do I convert my road bike gearing to fixed gear?
Follow these steps:
- Identify your most used road gear (often 50:15 or 50:17)
- Calculate its gear inches (~87" for 50:17 on 700c)
- Choose fixed gear ratio with similar gear inches
- Adjust for fixed gear's constant engagement (slightly lower)
- Example: Road 50:17 → Fixed 48:17 or 49:18
Should I prioritize ratio or cadence?
It depends on your riding style:
| Riding Style | Priority | Typical Cadence | Example Ratio |
|---|---|---|---|
| Spinner | Higher cadence | 90-110 RPM | 46:17 |
| Masher | Lower cadence | 65-85 RPM | 51:15 |
| Balanced | 80-100 RPM | Medium | 48:17 |