Gear Ratio Calculator

Notes — methodology

1. §1

   Ratio and development

   Gear ratio is chainring teeth divided by cog teeth. Development is the distance traveled per crank revolution: ratio × wheel circumference. Circumferences are measured rollout values per tire size, not nominal diameters.

   Source: Sheldon Brown, Gear Theory
2. §2

   Speed at cadence

   Speed = development × cadence. The chart assumes the cadence set in the margin; it is a gearing ceiling, not a physiological claim.

   Source: docs/methodology/gear-ratio.md
3. §3

   Cross-chaining

   Flagged combinations follow the conventional rule: big ring with the two largest cogs, or small ring with the two smallest. They work, but wear faster and waste watts — struck through in the chart, dashed in the scale.

   Source: Sheldon Brown, Derailer Adjustment
4. §4

   Range

   Range is the hardest ratio over the easiest, minus one, as a percent. A 10–44 cassette on a 1x is 340%; comparing ranges only makes sense at equal tire size — this sheet holds tire constant across A and B.
5. §5

   Climb test

   For the easiest gear, we solve the steady-state power balance — gravity, rolling, and aero resistance against your set power and mass — for road speed on the climb's average gradient, then convert to cadence. Below ~60 rpm the gear is likely too tall. Defaults: Crr 0.005, CdA 0.40 m², drivetrain efficiency 0.97.

   Source: Martin et al. (1998), J. Appl. Biomech.