Gear, RPM & drivetrain calculations without guesswork.
Use practical calculators for gear ratios, road speed, sprockets, pulleys, chain length, bicycle gearing and tire-size effects. No signup. The math runs in your browser.
15-tooth driver → 45-tooth driven gear
Start with the calculation you actually need.
Gear Ratio Calculator
Use tooth counts from a simple gear pair to see the reduction or overdrive ratio, output shaft speed and torque multiplication.
Open calculator →DrivetrainRPM to Speed Calculator
Estimate vehicle speed at a given engine RPM from the selected gear, differential ratio and rolling diameter.
Open calculator →MotorcycleMotorcycle Sprocket Change Calculator
Compare a front/rear sprocket change before buying parts. The tool reports ratio change, same-speed RPM change and theoretical same-RPM speed change.
Open calculator →DrivetrainMulti-Gear Speed Calculator
Paste a list of gear ratios and see a complete speed-by-gear table at one engine RPM.
Open calculator →BicycleCycling Cadence to Speed Calculator
Estimate bike speed from cadence and gearing without needing a power model.
Open calculator →TiresTire Diameter Calculator
Turn a standard metric tire size into overall diameter and circumference for gearing calculations.
Open calculator →Not a wall of nearly identical SEO pages.
Each GIIRR calculator solves a different mechanical or cycling problem. Every tool shows its assumptions, formula and a worked example so you can understand the result rather than copy a number blindly.
- Separate calculations for gears, sprockets, belts, tires and bicycles.
- Unit conversions are handled in-browser.
- No vehicle database or hidden “magic” assumptions.
- Critical limitations are stated on each tool page.
Short guides for the concepts behind the tools.
How Gear Ratios Work: Speed & Torque
A practical guide to gear ratio, reduction, overdrive, output RPM and torque multiplication.
Read guide →How Tire Size Changes RPM & Speed
Understand how tire diameter changes effective gearing, highway RPM and speedometer error.
Read guide →Motorcycle Sprocket Changes Explained
A practical explanation of motorcycle final gearing, acceleration, cruise RPM and theoretical top-speed changes.
Read guide →Bicycle Gearing: Ratios, Gear Inches & Cadence
Compare bicycle gears using mechanical ratio, gear inches and cadence-to-speed calculations.
Read guide →