Bike Gear Ratio Calculator
Calculate gear ratios, gear inches, and development
What is Gear Ratio?
Gear ratio is the relationship between your front chainring (the gear attached to your pedals) and your rear cog (the gear on your rear wheel). It determines how many times your rear wheel rotates for each complete pedal revolution.
A higher gear ratio means your wheel turns more times per pedal stroke, which is great for speed on flat terrain. A lower gear ratio makes pedaling easier, which is ideal for climbing steep hills.
How to Calculate Gear Ratio
The formula is simple: Gear Ratio = Chainring Teeth ÷ Rear Cog Teeth.
If you have a 50-tooth chainring and a 25-tooth rear cog:
50 ÷ 25 = 2.0
Your gear ratio is 2.0, meaning your rear wheel rotates twice for every pedal revolution.
Understanding Gear Inches and Development
Gear Inches is a traditional measurement from the penny-farthing era. It represents the effective diameter of the wheel if the pedals were directly attached to it. The formula is:
Gear Inches = Gear Ratio × Wheel Diameter (inches)
Development (also called Meters of Development) is the distance your bike travels forward with one complete pedal revolution. It's calculated as:
Development = Gear Ratio × Wheel Circumference
Higher development means you travel farther per pedal stroke, but it requires more force.
What are Good Gear Ratios?
The "ideal" gear ratio depends entirely on the terrain and your riding style:
- Climbing (1.0 - 1.5): Low gear ratios make steep climbs manageable. Common setups: 30T chainring with 28-34T cogs. Gear inches: 20-35 inches.
- Flat Terrain (2.0 - 3.0): Moderate ratios balance speed and efficiency. Common setups: 39-42T chainring with 13-21T cogs. Gear inches: 60-85 inches.
- Sprinting (3.5 - 5.0+): High ratios maximize speed on descents or flat sprints. Common setups: 50-53T chainring with 11-15T cogs. Gear inches: 90-120+ inches.
Professional cyclists often use gear ratios above 4.0 during sprints, while recreational riders typically stay in the 2.0-3.0 range for comfort and efficiency.
Limitations
Gear ratio calculations assume perfect conditions and don't account for:
- Tire pressure and tread (which affect actual wheel circumference)
- Chain efficiency losses (typically 2-3% power loss)
- Rider power output, fitness level, and cadence preferences
- Wind resistance, road surface, and bike weight
Use this calculator as a starting point, and adjust based on your personal riding experience and terrain.
Frequently Asked Questions
What is a gear ratio on a bike?
Gear ratio is the relationship between the front chainring teeth and rear cog teeth. It determines how many times the rear wheel rotates for each pedal revolution. Formula: Chainring Teeth ÷ Rear Cog Teeth.
What are Gear Inches?
Gear Inches represents the effective wheel diameter based on your gear ratio. It comes from penny-farthing bicycles where pedals directly drove the wheel. Higher gear inches mean harder pedaling but more distance per pedal stroke.
What is Development in cycling?
Development (or Meters of Development) is the distance your bike travels forward with one complete pedal revolution. It is calculated by multiplying the gear ratio by the wheel circumference.
What is a good gear ratio for climbing?
For climbing steep hills, lower gear ratios (1.0 to 1.5) are ideal. This typically means a small chainring (30-34T) paired with a large rear cog (28-34T or larger). Lower ratios make pedaling easier on inclines.
What gear ratio is best for flat terrain?
For flat roads or slight inclines, moderate gear ratios (2.0 to 3.0) work well. This balances speed and efficiency, using mid-size chainrings (39-42T) with mid-range cogs (13-21T).