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, and every calculator can share its exact inputs or compare saved scenarios.
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 →One focused calculator for each mechanical decision.
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.
- Shareable setup links preserve the exact inputs you choose.
- Save and compare up to six scenarios locally on each calculator.
- No vehicle database or hidden “magic” assumptions.
- Critical limitations are stated on each tool page.
Calculate once. Compare the decisions that matter.
Calculate
Use your own dimensions, ratios, RPM or tire sizes instead of a generic example.
Save variants
Keep up to six setups locally in your browser without creating an account.
Compare two
Select any two saved scenarios to see changed inputs and calculated outputs side by side.
Share or export
Send an exact setup link or export saved scenarios as CSV for your notes or build sheet.
What do you need to change?
A ratio is rarely the whole decision. Choose the first quantity you can measure, then follow the next calculation before selecting hardware.
| Your task | Calculate first | Then check |
|---|---|---|
| Size a two-sprocket chain drive | Sprocket ratio & output RPM | Chain velocity and whole-link length |
| Choose belt-drive pulleys | Driven-shaft RPM | Belt speed and manufacturer limits |
| Compare motors and gearboxes | Torque from kW & RPM | Gearbox torque & efficiency |
| Lay out external spur gears | Basic shaft spacing | Tooth ratio and the actual tooth profile |
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 →Chain Drive Design: Speed, Ratio & Length
Plan a two-sprocket roller-chain drive from output RPM and chain velocity to center spacing, chain pitches and fitment checks.
Read guide →Belt Drive Sizing: Pulleys, Speed & Slip
Learn pulley speed ratios, effective diameter, belt velocity, slip and the checks required before changing a two-pulley drive.
Read guide →Motor Power, Torque & RPM Explained
Understand kW-to-torque conversion at a shaft, motor nameplate assumptions, duty ratings and gearbox power losses.
Read guide →Spur Gear Module & Center Distance Guide
Use tooth counts and metric module to estimate external spur-gear pitch diameters and center spacing, then account for profiles and design constraints.
Read guide →