Fixed Gear Ratio Calculator
Your fixed gear at a glance: ratio, skid patches, gear inches.
Drivetrain
Circumference, mm
Can skid with either foot forward — doubles your skid patches and spreads tyre wear so the tyre lasts longer.
Close gears ±2%
Cadence / Speed
This calculator works out the three numbers that matter on a fixed gear: gear ratio (chainring over cog), skid patches — how many spots on the tyre wear when you lock the rear wheel, and development — how far you roll per crank turn (gear inches in imperial). How each one works is covered in the FAQ below.
The close-gears table lists every chainring/cog pair within ±2% of your current ratio; the tiles are clickable and load that gear straight away. Under it, speed at cadences from 50 to 130 rpm, in km/h or mph, on the same unit toggle.
FAQ
What is a skid patch?
It is one of the positions the rear wheel stops in during a skid. However many positions there are, that many spots on the tyre wear. Patch count = rear cog divided by its GCD with the chainring.
Why does ambidextrous skidding sometimes double the patches and sometimes not?
Doubling only happens when the chainring is odd after dividing by the GCD. Take 48×15: the GCD is 3, 48/3 = 16 which is even, so switching feet adds nothing — still 5 patches. But 44×16 goes from 4 to 8.
How is development different from gear inches?
Two views of the same gear. Development is metres per crank revolution — the metric view. Gear inches is the equivalent wheel diameter in inches (ratio × diameter) — the imperial view. The unit toggle switches between them.
Which wheel circumference should I pick?
Pick a size from the list — the values follow ETRTO geometry, like most calculators. For an exact figure for your actual tyre, roll the wheel one full turn from a marked point, measure the distance, and type it into the custom field.