The method behind your pressure.

01Start with the principle.

Pressure affects tire deflection, contact and support. Greater loads generally need more support; wider tires can generally achieve useful deflection at lower pressure. Surface-induced vibration, casing and impacts also matter, so each has its own adjustment.

We use an empirical reference-curve model with multiplicative corrections. It provides a reproducible starting point; the ideal gas law alone does not determine an optimal riding pressure.

P

Unrounded pressure for each wheel in PSI; conversion and rounding happen last.

P₆₈

Reference mean pressure at 68 kg total, 622 mm bead-seat diameter, standard casing, hookless tubeless, mixed/dry surfaces and normal impacts.

w / D

w is estimated mounted tire width; D is bead-seat diameter, both in mm.

K

Dimensionless weight, wheel-position, surface, casing, system, wetness and impact factors, detailed below.

02Width selects the reference pressure.

Enter the width printed on the sidewall. When internal rim width is provided, we first estimate mounted width; when it is blank, labeled width is used directly. The 0.4 coefficient is a generic estimate, not an exact expansion rate for every tire.

I is internal rim width. Iref is linearly interpolated from the table, using 17 mm at labeled widths ≤23 mm and 35 mm at ≥70 mm. The public form uses labeled widths; the engine’s internal measured-width mode uses the measurement without a second correction.

Three riding categories, three complete curves.

The charts read all anchors directly from the program, in mm/PSI. Between adjacent anchors we interpolate linearly; outside the curve we do not extrapolate. Curves cover geometry-adjusted widths, so their extra anchors do not expand the form’s labeled-width scope.

Each vertical axis starts at zero, with its own labeled scale.

03One total weight. Two wheel pressures.

M is rider + bike + gear and water in kg. Count each item only once. Starting from 68 kg, each additional kilogram raises reference pressure by 0.6%; lower weight follows the same formula.

Without measured wheel loads

The default front/rear factors are 0.97/1.03, making rear pressure about 6.2% higher with matching setups. These factors define the default pressure distribution; measured wheel loads can be entered under More settings.

With measured wheel loads

Lwheel is the measured load on that wheel in kg. This replaces, rather than multiplies, the default 0.97/1.03 factors. Equal loads and setups produce equal pressures; a more heavily loaded front wheel can have higher pressure. Measured loads already include the bike and gear; their weight is not added again to each wheel.

Diameter correction uses bead-seat diameter: 622 mm for 700C/29-inch and 584 mm for 650B/27.5-inch; XC also supports 559 mm. The factor is (622/D)^0.3, not a calculation using “700” or “29”.

04Every adjustment, in view.

Tire setup + rim type

Rim corrections combine bike-shop technicians’ setup experience with riders’ on-road feedback, using empirical factors for each tire and rim pairing. Hookless tubeless is the baseline; hooked tubeless starts about 7.85% higher. Inner tubes and rims use one combined correction.

Apply the selected combined factor once per wheel, without stacking separate tube and rim allowances. The internal-width correction is applied once, separately.

Factors are displayed to at most 6 decimal places; calculations use full precision.

These are empirical model factors, not a claim that all wheelsets have identical physical behavior. A tube + hookless pairing still requires a hookless-compatible tire; an unknown rim remains an unverified configuration.

Surface, casing, wetness & impacts

Surface, casing, wetness and impact factors multiply. Surface texture addresses comfort and contact, while impact level adds a separate support allowance.

05Turn the result into your starting setup.

1. Enter actual rider, bike and gear weights, labeled sidewall widths, and internal rim widths when known.
2. Select tire setup, rim type, surface and conditions. Enter separate front/rear settings when needed, and recalculate after changes.
3. Use a reliable gauge on cold tires near riding conditions. This release does not automatically compensate for temperature, altitude, sunlight or braking heat.
4. Start from the result, change one variable at a time on familiar terrain and make small adjustments. The ±5% tuning window is neither a safety range nor a statistical confidence interval.

Convert and round last

Internally we use kg, mm and PSI. 1 lb = 0.45359237 kg; 1 in = 25.4 mm; 1 BAR = 14.503773773 PSI. PSI is shown as an integer and BAR to two decimals, both derived from unrounded PSI, without cumulative unit-switching error.

Current input and output scope

• Labeled widths: road 23–35 mm; gravel 35–55 mm; XC 50–65 mm. Road hookless requires at least 28 mm.
• Rider 30–140 kg, bike 3–35 kg, gear 0–40 kg, total 50–150 kg. Internal rim width may be 15–40 mm and must be below the entered tire width; this geometry check is not compatibility certification.
• Measured wheel loads must each be 18–90 kg; their sum must match total mass within the greater of 1 kg or 2%.
• Unrounded output must be 10–140 PSI and inside the reference curve. Entered limits must be 1–200 PSI, with the minimum below the maximum. Invalid inputs, explicit incompatibility, conflicting bounds or either wheel exceeding a limit produce no pair of recommendations.

Inputs are calculated on your device

No login is required; weights and equipment parameters are used on your device and are not uploaded to a server. Persistence is off by default; Remember settings stores inputs in this browser only. Uncheck it or reset to clear them. Refresh restores saved inputs, not old results; navigating to this guide and back retains inputs in the same page session.

06References

The references below explain tire width, load, deflection, compatibility and pressure limits. Calculations run independently on your device using the parameters published on this page.

• Bicycle Quarterly / Frank Berto ↗

  Background on load, width and tire deflection. The current anchors are not a direct copy of the original 15% tire-drop curve.

• Schwalbe ↗

  Hookless tire compatibility, labeled sizes and pressure requirements. Installing a tube does not remove tire-compatibility requirements.

• Continental ↗

  Tire/rim pairing and manufacturer requirements; use the stricter applicable limits.