What are gear inches and why do they matter?

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.

What is development in cycling gearing?

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.

How does tyre width affect gear inches?

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 increases the effective diameter by about 8 mm, adding approximately 1 gear inch. This is why the calculator asks for tyre width — it gives more accurate results than using nominal rim diameter alone.

What cadence should I aim for on the road?

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.

How do I choose the right gear for climbing?

For sustained climbing, aim for a gear that lets you maintain 75 to 90 rpm without excessive muscular effort. Many cyclists find that a gear giving 5 to 7 km/h at 80 rpm is manageable on steep gradients. If you frequently need to push below 5 km/h on climbs, consider a lower gear ratio (larger cog or smaller chainring).

BikeCalcs

Gear Inch Calculator — Development, Speed at Cadence

Calculate gear inches, development in metres and speed at cadence 80, 90 and 100 rpm for any wheel and drivetrain combination.

Chainring Teeth

Front chainring tooth count (e.g. 50T large ring, 34T small ring)

Cog Teeth

Rear cassette sprocket tooth count (e.g. 17T for a mid-cassette gear)

Wheel SizeWheel standard — determines ISO rim diameter used in calculation

Tyre Width

Stated tyre width in mm (e.g. 25 for 700×25c, 2.1in = ~53 mm)

How We Calculate This

Gear Inches Formula

Gear Ratio = Chainring teeth ÷ Cog teeth

Effective diameter (mm) = Rim diameter (ISO mm) + 2 × tyre width × 0.9

Gear Inches = Gear ratio × effective wheel diameter (inches)

Development

Development (m) = Gear ratio × wheel circumference (m)

Wheel circumference = π × effective diameter in metres.

Speed at Cadence

Speed (km/h) = Development (m) × cadence (rpm) × 60 ÷ 1,000

Tyre width uses a section-height factor of 0.9 (90% of stated tyre width) for a typical clincher tyre inflated to normal pressure.

Frequently Asked Questions

Related Calculators

Gear Ratio Calculator

Calculate gear ratios from chainring and sprocket tooth counts.

Gear Inches Calculator

Convert gear ratios to gear inches for comparison.

Development Calculator

Calculate distance travelled per pedal revolution for any gear.

Chainring Calculator

Compare chainring sizes and their effect on gearing range.

Cassette Calculator

Analyse cassette tooth counts and gear jumps between sprockets.

Last updated: March 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.