Bike Gear Calculator
Our cycling calculator computes bike gear instantly. Get accurate stats with historical comparisons and benchmarks. Enter your values for instant results.
Reviewed for accuracy by Sher, Sports Science & Nutrition Specialist
Bike Gear Calculator
Calculator
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Formula: Gear Ratio = Chainring Teeth / Cog Teeth
Worked example — Ratio: 2.941 | Development: 6.93 m | Speed: 37.4 km/h (23.2 mph)
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 Wheel Circumference = (700 + 2 x 25) x PI / 1000 = 2.356 m Development = 2.941 x 2.356 = 6.93 m per revolution Speed = 6.93 x 90 x 60 / 1000 = 37.4 km/h Gear 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 Wheel Circumference = (700 + 2 x 28) x PI / 1000 = 2.375 m Development = 1.214 x 2.375 = 2.884 m per revolution Speed = 2.884 x 80 x 60 / 1000 = 13.8 km/h Gear 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.
How do I choose the right chainring and cassette combination?
Choosing the right chainring and cassette depends on your fitness level, terrain, and riding style. For flat terrain and fast riding, a compact crankset with 50/34 chainrings paired with an 11-28 cassette covers most situations well. For hilly areas, consider a wider range cassette like 11-32 or 11-34 to provide easier climbing gears. Stronger riders may prefer a standard crankset with 53/39 chainrings for higher top-end speed. Mountain bikers typically use a single chainring between 30 and 34 teeth with a wide-range cassette like 10-51. The key is ensuring adequate gear range without excessive overlap between chainring and cassette combinations, which wastes potential ratios and increases chain wear.
What is gain ratio and why did Sheldon Brown develop it?
Gain ratio is a gearing measurement developed by the late cycling expert Sheldon Brown to provide a more complete picture of mechanical advantage than gear inches or development alone. The gain ratio accounts for crank length by dividing the development by the circumference traced by the pedals (2 times pi times crank length). This matters because longer cranks provide more leverage, effectively making a gear easier to push. A gain ratio of 5.0, for example, means the bicycle travels 5 times the distance that the foot moves. Gain ratio typically ranges from 2.0 for easy climbing gears to about 9.0 for top sprint gears. It is the only gearing measurement that allows fair comparison between bikes with different crank lengths.
How does cadence affect speed in different gears?
Cadence is the number of complete pedal revolutions per minute, and it directly multiplies with gear development to determine speed. The formula is straightforward: speed equals development times cadence times 60 divided by 1000 for km/h. At 90 RPM in a 50/17 gear with a 700c wheel, you travel at approximately 38 km/h. Increasing cadence to 100 RPM in the same gear bumps speed to about 42 km/h. Professional cyclists typically maintain cadences between 85 and 105 RPM, while recreational riders often pedal at 60 to 80 RPM. Higher cadences are generally more efficient for sustained efforts because they reduce muscular fatigue, though they increase cardiovascular demand. Finding your optimal cadence requires experimentation and training.
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 does wheel size affect gearing calculations?
Wheel size directly changes the distance traveled per pedal revolution by altering the wheel circumference. A 700c road wheel with a 25mm tire has a circumference of approximately 2111 mm, while a 650b wheel with a 47mm tire measures about 2090 mm. Even within the same nominal size, tire width matters because wider tires increase the effective diameter. A 700x23 tire gives a circumference roughly 20mm smaller than a 700x32 tire. Mountain bike wheels at 29 inches are actually the same rim diameter as 700c but use much wider tires, resulting in larger overall circumference. When comparing gearing between bikes with different wheel sizes, always use development or gain ratio rather than simple gear ratios to get meaningful comparisons.
What is cross-chaining and should I avoid it?
Cross-chaining occurs when you use the big chainring with the biggest rear cog, or the small chainring with the smallest rear cog, creating a diagonal chain line. This extreme angle increases chain wear, produces more drivetrain noise, and reduces power transmission efficiency by 1 to 3 percent compared to a straight chain line. Most cycling coaches recommend avoiding the largest and smallest two cogs when in each chainring. Modern drivetrains with clutch derailleurs and wider-range cassettes handle cross-chaining better than older systems, but the wear penalty still exists. One advantage of single-chainring setups (1x drivetrains) is eliminating cross-chaining entirely since there is only one chainring to create chain angle with.
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.
References
Reviewed for accuracy by Sher, Sports Science & Nutrition Specialist · Editorial policy
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