Gear Inch Calculator — Development, Speed at Cadence

Gear inches represent the equivalent wheel diameter (in inches) of a directly-driven penny-farthing bicycle. A higher gear inch value means a harder gear that covers more ground per pedal revolution. Gear inches allow you to compare gears across bikes with different wheel sizes, chainring sizes and cassette sizes on a single scale.

Development (sometimes called rollout) is the distance your bicycle travels with one full pedal revolution. It is calculated as gear ratio multiplied by wheel circumference. A development of 8 metres means every complete pedal turn moves you 8 metres forward. Higher development = faster at a given cadence.

A wider tyre increases the effective rolling diameter of the wheel, which slightly increases gear inches and development. Going from a 23 mm to a 32 mm tyre on 700c wheels raises the wheel radius by about 8 mm per side, so the effective diameter grows by roughly 16 mm — adding about 1 to 2 gear inches depending on the ratio (close to 2 gear inches at a hard 50/17 gear). This is why the calculator asks for tyre width — it gives more accurate results than using nominal rim diameter alone.

Most road cyclists aim for 85 to 95 rpm as an efficient aerobic cadence. A cadence of 80 rpm is comfortable for steady riding, 90 rpm is efficient and reduces muscular fatigue on long rides, and 100 rpm is typical for climbing or sprint warm-ups. Track sprinters may spin well above 120 rpm.

For sustained climbing, aim for a gear that lets you maintain 75 to 90 rpm without excessive muscular effort. A typical road compact climbing gear (for example 34/32 on 700c, roughly a 1:1 ratio) gives about 9 to 12 km/h at 80 rpm. Very low sub-1:1 gears used for steep off-road riding or heavily loaded touring drop that to around 5 to 7 km/h at 80 rpm, which is what you want when the gradient gets severe. If you frequently grind to a near-standstill on climbs, consider a lower gear ratio (larger cog or smaller chainring).