About GIIRR

GIIRR is a focused collection of free calculators for gear ratios, rotational speed, chain and belt drives, bicycle gearing and tire-size effects.

Why the site exists

Many mechanical calculations are simple enough to do by hand but easy to get backward. GIIRR puts the formula next to the result, keeps inputs explicit and avoids pretending to know vehicle-specific facts that were never supplied.

What GIIRR does not do

GIIRR is not a fitment database, service manual, legal speed-calibration service or engineering sign-off. Results are theoretical estimates based on the values you enter.