BMX Gear Ratio Calculator
Calculate your BMX gear ratio, gear inches, and rollout distance. Find the optimal setup for street, park, or racing.
Common sizes: 25, 28, 30, 33, 36
Common sizes: 9, 10, 11, 12
Gear Ratio = Chainring Teeth / Cog Teeth; Gear Inches = Gear Ratio x Wheel Diameter
Example: 25-tooth chainring with 9-tooth cog on a 20 inch wheel = 2.78:1 ratio, 55.6 gear inches - perfect for all-around street/park riding
What is a good BMX gear ratio?
Most BMX riders use 2.5:1 to 2.9:1. Common setups are 25/9 (2.78), 28/10 (2.80), or 25/10 (2.50). Racers prefer higher ratios; street riders prefer lower.
What are gear inches?
Gear inches = ratio x wheel diameter. It represents the equivalent wheel size of a direct-drive bike. Higher gear inches = more speed but harder to pedal.
Should I change chainring or cog?
Smaller cog = harder gear, faster top speed. Smaller chainring = easier gear, better acceleration. Changing cog is usually easier and cheaper.
📐 Formula
Gear Ratio = Chainring Teeth / Cog Teeth; Gear Inches = Gear Ratio x Wheel Diameter
📝 Example Calculation
Example: 25-tooth chainring with 9-tooth cog on a 20 inch wheel = 2.78:1 ratio, 55.6 gear inches - perfect for all-around street/park riding
❓ Frequently Asked Questions
What is a good BMX gear ratio?▼
Most BMX riders use 2.5:1 to 2.9:1. Common setups are 25/9 (2.78), 28/10 (2.80), or 25/10 (2.50). Racers prefer higher ratios; street riders prefer lower.
What are gear inches?▼
Gear inches = ratio x wheel diameter. It represents the equivalent wheel size of a direct-drive bike. Higher gear inches = more speed but harder to pedal.
Should I change chainring or cog?▼
Smaller cog = harder gear, faster top speed. Smaller chainring = easier gear, better acceleration. Changing cog is usually easier and cheaper.