What This Tool Does
This bike gear ratio calculator helps cyclists understand their drivetrain's performance characteristics. It calculates gear ratios, gear inches, development, and potential speeds for any chainring and cassette combination. Whether you're setting up a new bike, planning a gear upgrade, or analyzing your current setup, this tool provides the metrics you need to optimize your gearing for your riding style and terrain.
How to Use the Calculator
- Choose a preset or enter your custom chainring and cassette specifications
- Enter your chainring teeth - big chainring and small chainring (if you have one)
- Enter your cassette range - smallest and largest cog teeth counts
- Set your wheel diameter - typically 27" for 700c road wheels or 27.5"/29" for mountain bikes
- Enter your target cadence - most cyclists aim for 80-100 RPM
- Click Calculate to see your complete gear analysis and chart
Example: A road bike with 50/34 chainrings and an 11-28 cassette on 700c wheels (27") gives you a highest gear ratio of 4.55 (50/11) and lowest of 1.21 (34/28). At 90 RPM cadence, your max speed would be approximately 32 mph, and your climbing gear provides 33 gear inches for steep gradients.
Understanding Gear Metrics
Gear Ratio
The gear ratio is calculated by dividing the number of teeth on the chainring by the number of teeth on the rear cog. A ratio of 4.0 means the rear wheel turns 4 times for every pedal revolution. Higher ratios are for speed, lower ratios are for climbing.
Gear Inches
Gear inches represents how far your bike travels with one pedal revolution if you had a penny-farthing bicycle. It's calculated by multiplying the gear ratio by the wheel diameter. This traditional metric remains popular because it provides an intuitive sense of how "hard" or "easy" a gear feels.
Development
Development is the distance (in meters) your bike travels with one complete pedal revolution. It's the metric equivalent of gear inches and is commonly used in Europe. Development = Gear Ratio × Wheel Circumference.
Speed at Cadence
This shows the theoretical speed you'll achieve in each gear at your target cadence (pedaling rate). Most efficient cyclists maintain 80-100 RPM on flat terrain and 60-80 RPM when climbing.
Common Gearing Setups
Road Racing (53/39 × 11-28)
Traditional racing gearing provides high top-end speed with a 53-tooth big ring. The 39-tooth small ring and 28-tooth large cog offer sufficient climbing ability for most terrain.
Compact Road (50/34 × 11-28 or 11-32)
The most popular road setup today. The 50/34 "compact" crankset paired with 28 or 32-tooth max cog provides excellent versatility for mixed terrain, gran fondos, and recreational riding.
Gravel/Adventure (46/30 × 11-36 or 10-44)
Gravel bikes use smaller chainrings and wider-range cassettes for tackling unpaved climbs and varied terrain. This provides lower gears for steep off-road sections while maintaining reasonable top-end speed.
Mountain Bike (32 or 34 × 11-50 or 10-52)
Modern mountain bikes typically use a single front chainring (32-34 teeth) with an extremely wide-range cassette. This provides low gears for technical climbing and sufficient high gears for descents.
Choosing the Right Gearing
For flat terrain and racing: Prioritize higher gear ratios (bigger chainrings, smaller max cog) for maintaining speed at high cadence.
For hilly or mountainous riding: Choose lower gear ratios (smaller chainrings, larger max cog) to maintain comfortable cadence on climbs.
For mixed terrain: Balanced gearing (compact or semi-compact crankset with moderate cassette range) provides versatility.
For touring or bikepacking: Prioritize very low gear ratios (triple crankset or wide-range cassette) to handle loaded climbing.
Assumptions and Notes
- Speed calculations assume no wind resistance, rolling resistance, or gradient
- Actual speeds will vary based on rider power, aerodynamics, and environmental conditions
- 700c road wheels are approximately 27" diameter; 650b is approximately 27.5"
- Tire width affects actual wheel diameter; wider tires increase effective diameter slightly
- Most cassettes don't include every cog size between smallest and largest
- Cross-chaining (big-big or small-small combinations) should be avoided for drivetrain longevity
Frequently Asked Questions
What is a good gear ratio for climbing?
For road cycling, gear ratios below 1.5 (such as 34/28 = 1.21 or 34/32 = 1.06) are considered good for climbing. For mountain biking, ratios below 1.0 (such as 32/34 = 0.94 or 32/50 = 0.64) help tackle steep technical climbs. The lower the ratio, the easier it is to maintain cadence on steep gradients.
What cadence should I aim for?
Most recreational cyclists perform well at 80-90 RPM on flat terrain. Competitive cyclists often maintain 90-100 RPM. When climbing, 60-80 RPM is typical. Higher cadence is generally more efficient and reduces muscle fatigue, but requires appropriate gearing to maintain.
Should I use a compact or standard crankset?
Compact cranksets (50/34) are more versatile and suitable for most riders, especially those tackling hills or longer rides. Standard cranksets (53/39) provide higher top-end speed for racing and flat terrain but offer less low-end range for climbing. Semi-compact (52/36) splits the difference.
What does "gear inches" actually mean?
Gear inches is a traditional metric from penny-farthing bicycles. It represents the diameter of an equivalent directly-driven wheel. A gear of 75 inches means one pedal revolution moves you as far as one revolution of a 75-inch wheel. Higher numbers = harder/faster gears; lower numbers = easier/slower gears.
Is 1x (single chainring) better than 2x?
1x drivetrains are simpler, lighter, and require less maintenance with no front derailleur. However, 2x systems provide wider total range and smaller jumps between gears. For road cycling and mixed terrain, 2x is often preferred. For mountain biking and gravel, 1x with a wide-range cassette has become the standard due to simplicity and sufficient range.
How do I know what cassette I have?
The cassette range is usually marked on the largest cog (e.g., "11-28" or "10-50"). You can also count the teeth on the smallest and largest cogs. Common road cassettes include 11-28, 11-30, 11-32, and 11-34. Mountain bike cassettes range from 11-42 up to 10-52.
Can I calculate speed for different cadences?
Yes, speed is directly proportional to cadence. If the calculator shows 20 mph at 90 RPM, you'll achieve approximately 22.2 mph at 100 RPM or 18 mph at 80 RPM in the same gear. Adjust the target cadence input to see speeds for your preferred pedaling rate.