Last updated: 2026-06-29

How bicycle gearing works

Every time you push the pedals one full rotation, the chain pulls the rear wheel around by a number of rotations determined by the tooth counts on your chainring and rear cog. This relationship — the gear ratio — is the foundation of all bicycle gearing analysis:

$\text{Gear ratio} = \frac{T_c}{T_s}$

where $T_c$ is chainring teeth and $T_s$ is cog teeth. A 50-tooth chainring paired with a 14-tooth cog produces a ratio of $50 / 14 \approx 3.57$: the rear wheel turns 3.57 times for each full pedal revolution.

From ratio to real-world distance

The gear ratio alone doesn't tell you how far the bike travels per pedal stroke, because that depends on wheel size. Two metrics capture this:

Development (roll-out)

$d = G \times \pi \times D_w$

where $G$ is the gear ratio and $D_w$ is the effective wheel diameter in metres. Development is the distance the bike advances per pedal revolution. A road race gear with ratio 3.5 on a 700c × 28 mm wheel (diameter ≈ 0.680 m) gives:

$d = 3.57 \times \pi \times 0.680 \approx 7.63 \text{ m}$

Gear inches

$GI = G \times D_w^{\text{(in)}}$

Gear inches is a legacy metric dating from penny-farthing bicycles — it represents the diameter (in inches) of a directly-driven wheel that would cover the same distance per pedal stroke. Unlike development, it omits the π factor:

$GI = G \times \frac{D_w}{0.0254}$

The two metrics are proportional: $GI \approx d \times \frac{39.37}{\pi} \approx d \times 12.53$. Development is more useful for modern training analysis; gear inches remain popular in English-language cycling literature and comparison charts.

Speed from cadence

Multiply development by cadence (in rev/s) to find ground speed:

$v = d \times \frac{\omega}{60}$

where $\omega$ is cadence in rpm. At 90 rpm in a 50 × 14 gear on 700c × 28 mm wheels:

$v = 7.63 \times \frac{90}{60} \approx 11.4 \text{ m/s} = 41.2 \text{ km/h}$

Choosing gears

A useful rule of thumb: stay within a cadence range of 80–100 rpm and pick the gear that puts your target speed in that window. If you're spinning above 100 rpm, shift to a higher (harder) gear; if you're grinding below 70 rpm, shift to a lower (easier) gear.

When comparing setups across different wheel sizes, always use gear inches or development — raw tooth ratios are misleading because a 29″ MTB wheel covers about 16 % more ground per revolution than a 26″ wheel at the same ratio.

Effective wheel diameter

Wheel presets in this calculator use the effective rolling diameter: the bead seat diameter of the rim plus twice the inflated tyre section height. For a 700c rim (622 mm bead seat) with a 28 mm tyre, the effective diameter is approximately $622 + 2 \times 28 = 678$ mm. Measure your specific tyre at riding pressure for the best accuracy — tyre diameter can vary by several millimetres from one brand to the next.