Gear ratio and development
The gear ratio is chainring / sprocket (e.g. 50 × 11). Development (rollout) is the distance covered per pedal turn: ratio × wheel circumference. Gear inches is the ratio × wheel diameter in inches. Speed follows from your cadence (pedal revolutions per minute).
Where does the suggested pressure come from?
It targets about 15% tyre drop under each wheel's load (Frank Berto's method), then adjusts for terrain and tubeless. It is a starting point: fine-tune in steps of 1 to 3 psi for comfort and grip.
Always stay between the minimum and maximum pressures printed on the tyre and the rim. Hookless rims are usually limited to 72.5 psi (5 bar).
How to use it
- Describe the drivetrain: teeth on the chainrings (e.g. 50/34) and cassette (11-32).
- Enter the wheel: rim size and tyre width (700×28c, 29×2.2…); the circumference is computed, or type the one you measured.
- Read the table and chart: development and speed for each combination at your chosen cadence. The chart reveals near-identical ratios (duplicates).
- Compare two setups to see what a wider cassette or a smaller chainring changes before you buy.
- Work out tyre pressure from your weight, the bike and luggage, tyre width and terrain.
Worked numbers (700×25c wheel, circumference ≈ 2.105 m)
- 50 × 11: ratio 4.55, development ≈ 9.57 m per crank turn; at 90 rpm that is about 51.7 km/h.
- 34 × 28: ratio 1.21, development ≈ 2.56 m; at 80 rpm about 12.3 km/h, enough for an 8% climb.
- Going from an 11-28 to an 11-32 cassette gives 2.24 m in 34 × 32, a 12.5% shorter bottom gear for climbs, at the cost of slightly bigger jumps between sprockets.
Choosing your pressure
- Weight is not shared equally: roughly 40% on the front and 60% on the rear. The rear tyre therefore runs a little higher.
- Wider tyres run at lower pressure for the same tyre drop: more comfort and grip, and often less rolling resistance on rough roads.
- In the wet or on cobbles, drop 0.2–0.3 bar (3–4 psi). Tubeless tyres can go a little lower with no risk of pinch flats.
- Check pressure at least once a week: road tyres naturally lose air.
Common mistakes
- Pumping to the tyre's maximum: it is a safety limit, not a recommendation. The bike gets harsh and grips less.
- Riding big-big or small-small: the chain runs at an angle, wears fast and gets noisy. The chart shows equivalent gears to use instead.
- Ignoring the hookless rim limit: 5 bar (72.5 psi) maximum, whatever the tyre.
Guide written and checked by Erwan Hautot · updated 5 November 2026.