Bike Gear Calculator
Our cycling calculator computes bike gear instantly. Get accurate stats with historical comparisons and benchmarks. Enter your values for instant results.
Formula
Gear Ratio = Chainring Teeth / Cog Teeth
The gear ratio determines mechanical advantage. Development equals gear ratio times wheel circumference. Speed equals development times cadence times 60 divided by 1000. Gear inches equal gear ratio times effective wheel diameter in inches.
Worked Examples
Example 1: Road Bike Standard Gear Calculation
Problem: Calculate speed and development for a 50-tooth chainring, 17-tooth cog, 700x25c wheel at 90 RPM cadence.
Solution: Gear Ratio = 50 / 17 = 2.941\nWheel Circumference = (700 + 2 x 25) x PI / 1000 = 2.356 m\nDevelopment = 2.941 x 2.356 = 6.93 m per revolution\nSpeed = 6.93 x 90 x 60 / 1000 = 37.4 km/h\nGear Inches = 2.941 x (750 / 25.4) = 86.8 inches
Result: Ratio: 2.941 | Development: 6.93 m | Speed: 37.4 km/h (23.2 mph)
Example 2: Climbing Gear Analysis
Problem: What speed does a 34-tooth chainring with a 28-tooth cog produce at 80 RPM on a 700x28c wheel?
Solution: Gear Ratio = 34 / 28 = 1.214\nWheel Circumference = (700 + 2 x 28) x PI / 1000 = 2.375 m\nDevelopment = 1.214 x 2.375 = 2.884 m per revolution\nSpeed = 2.884 x 80 x 60 / 1000 = 13.8 km/h\nGear Inches = 1.214 x (756 / 25.4) = 36.1 inches
Result: Ratio: 1.214 | Development: 2.88 m | Speed: 13.8 km/h (8.6 mph)
Frequently Asked Questions
What is a gear ratio and how does it affect cycling performance?
A gear ratio in cycling is the number of times the rear wheel rotates for each complete revolution of the pedals. It is calculated by dividing the number of teeth on the front chainring by the number of teeth on the rear cog. A higher gear ratio means more distance per pedal revolution but requires more force to turn, making it ideal for flat roads and downhill sections. A lower gear ratio produces less distance per revolution but is easier to pedal, which is essential for climbing hills and starting from a stop. Most road bikes offer ratios ranging from about 1.5 to 4.5, while mountain bikes typically range from 0.7 to 3.5 to handle steeper terrain.
What is gear development and why is it important?
Gear development, also called rollout, is the distance in meters that a bicycle travels for one complete revolution of the cranks in a given gear combination. It provides a more practical measurement than the raw gear ratio because it accounts for wheel size. Development is calculated by multiplying the gear ratio by the wheel circumference. A typical range for road cycling is 4 to 9 meters per crank revolution. Knowing your development helps you compare gearing across different wheel sizes and bike types. Track cyclists closely monitor development because race organizers sometimes restrict maximum gear development in junior categories to protect young riders from overexertion.
What are gear inches and how do they relate to modern cycling?
Gear inches is a traditional measurement from the penny-farthing era that expresses the effective wheel diameter as if you were riding a direct-drive bicycle. It is calculated by multiplying the gear ratio by the actual wheel diameter in inches. A gear of 72 inches, for example, is equivalent to riding a penny-farthing with a 72-inch front wheel. While development in meters has become more common in modern cycling, gear inches remain popular in the United States and among track cycling enthusiasts. Typical road cycling ranges from about 40 gear inches for easy climbing gears to over 120 gear inches for sprint gears. Gear inches allow easy comparison between different wheel sizes and drivetrain configurations.
What are skid patches and why do fixed-gear riders care about them?
Skid patches are the specific points on a tire that contact the ground when a fixed-gear rider locks the rear wheel to skid for braking. The number of skid patches equals the rear cog tooth count divided by the greatest common divisor of the chainring and cog teeth. More skid patches mean the tire wears more evenly because the same spots do not contact the ground every time. For example, a 49/17 combination gives 17 skid patches (excellent), while 48/16 gives only 1 (terrible for tire life). Fixed-gear riders should choose gear ratios with at least 8 to 10 skid patches to avoid rapid tire wear. Ambidextrous skidders who can lock either foot forward effectively double their skid patch count.
How do I calculate the gear range and percentage gaps between gears?
Gear range is expressed as the ratio of the highest gear to the lowest gear. For example, a 50/34 crankset with an 11-28 cassette gives a range of (50/11) divided by (34/28) = 4.55/1.21 = 3.74 or 374 percent. The percentage gap between adjacent gears in the cassette determines how smooth the shifting feels. Smaller gaps (10 to 13 percent) between cogs allow you to maintain optimal cadence when changing gear, while larger gaps (15 to 20 percent) create noticeable cadence jumps. Professional racing cassettes like 11-23 have tight 7 to 10 percent gaps for precise cadence control. Wide-range cassettes like 11-34 sacrifice smooth progression for climbing ability with gaps exceeding 15 percent at the large cog end.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.