// Tire Pressure Calculator
Most riders guess, copy a friend, or trust a number they can’t question. Megylla shows its work — a starting pressure built from published measurements and standards, bounded by hard safety limits, and explained line by line.
Free. No sign-in, no email. Road, gravel, mountain, plus and fat bikes.
A result from the live tool. Your numbers depend on your bike.
// The problem
Ask around and you’ll get a different answer every time. For a 28 mm tire and a 170 lb rider, published values run from about 56 to 93 psi. That’s not a rounding difference — it’s the spread between a harsh ride and a mushy one.
And precision is mostly an illusion: a new pump gauge is typically only accurate to 5–6%. More decimal places than your gauge can read is false precision dressed up as science.
Our answer is an honest starting point — plus the reasons behind it — held inside hard safety limits that can never be crossed.
// Where the science starts
In the foundational public work on bike tire pressure, Frank Berto measured tire deflection with a hydraulic jack, a scale and a dial gauge: 50 tires, 7 pressures (40–160 psi), 8 loads (20–220 lb). His study was published by Bicycle Quarterly.
He defined good pressure as the one giving 15% tire drop — deflection equal to 15% of tire width. In his framing, 13% rides harder and 17% rides softer. His chart covers 20–37 mm tires at 30–70 kg per wheel. (A 100 kg system on a 45/55 split gives 125/155 psi on 20 mm, and 45/53 psi on 37 mm.)
We’re honest about its limits: it’s the only public, measured model, but it stops at 37 mm and its tires date from the 1990s. So Megylla uses Berto as a check for narrow road tires, not as the whole answer.
Peer-reviewed support comes from Dell’Orto et al. (2023, Politecnico di Milano), who measured racing-tire stiffness against pressure, load, speed and temperature. The finding that shapes our model: higher pressure pays off mainly under heavy loads, and over-inflation at low load actually reduces cornering stiffness. More pressure is not more grip.
// What the evidence agrees on
Pressure falls steeply as tires get wider, and rises a little less than in step with load. Our fitted curve: about width^-1.06 and load^0.88.
Rougher surfaces want less pressure. Field testing found about 1 watt lost at 10 psi under the optimum, versus ~9 watts at 10 psi over. When in doubt, we round toward the safe side.
About 2.5 psi per 10 °C at road pressures; ~1 psi per 610 m of climbing. At fat-bike pressures it’s dramatic — set fat-bike pressure outside, at riding temperature.
// The data
We didn’t invent a formula and hope. We fitted it to real, published numbers — charts, tables and measured studies — then checked how close it lands.
| Source | Points |
|---|---|
| A leading wheel maker’s 2026 tubeless road & gravel charts | 561 |
| Front/rear mountain-bike ranges (same maker) | 154 |
| Plus & fat-bike tables, a major tire maker’s published tables (upper check for tubes), fat-bike snow guidance, and Berto’s measured chart | 43 |
| Total reference points | 758 |
Fit quality: the core curve was fitted to 491 road and gravel points for riders up to 220 lb, with an average error of 4.6% — inside the 5–6% accuracy of a typical new pump gauge.
Above 220 lb, the published charts flatten out. That looks like the chart maker’s own rim limits rather than physics, so we deliberately did not copy that plateau.
The model is built only from published charts, measurements and standards. That rule is enforced by the database schema itself — nothing else can shape it.
// How a number is made
Each step is explained in your result, so you can see exactly why your number is what it is. Safety is applied last — and it always wins.
pressure = 43.6 psi × (system weight / 80 kg)^0.881 × (37 / tire mm)^1.056 × (rim inner width / 23 mm)^-0.51. System weight is rider plus everything carried plus bike. Wider tires and wider rims mean lower pressure.
The surface you ride multiplies the number down — from smooth pavement (×1.00) to deep snow (×0.30). Full table below.
Plus tires ×1.12. No other class needs one.
Tubes off-road ×1.11 (no change on pavement). Wet ×0.95 (a product choice). E-bike adds 10 kg to the default bike weight.
Rear ~5% higher than front on road and gravel, ~8% on MTB, plus and fat; e-bikes add 1%. We deliberately don’t split pressure in proportion to load — a front tire run too soft can fold under hard braking.
A minimum set by tire class, tubes or tubeless, casing, riding style and inserts — so the tire is protected against pinch flats and rim strikes. When we raise a number to the floor, we say so.
The lowest of the tire’s printed max, the rim’s printed max, and the ETRTO hookless limit for that tire width. Rounded down at the cap. Within 5% of the cap you get a headroom warning, because heat and altitude raise pressure. If your weight calls for more than the cap, we tell you — and suggest a wider tire — rather than quietly trimming the number.
// Surface matters
Gravel in published charts runs about 23% below pavement for the same tire — a bigger effect than rim width. Each surface multiplies the base number:
| Surface | Factor (vs smooth pavement) |
|---|---|
| Smooth road | ×1.00 |
| Rough road / chip-seal | ×0.92 |
| Hardpack gravel | ×0.88 |
| Mixed gravel | ×0.82 |
| Cobbles | ×0.80 |
| Rocky trail | ×0.80 |
| Trail | ×0.75 |
| Groomed snow | ×0.75 |
| Loose gravel | ×0.70 |
| Mud | ×0.70 |
| Packed snow | ×0.62 |
| Soft snow | ×0.48 |
| Sand estimate | ×0.45 |
| Deep snow | ×0.30 |
Fat-bike results line up with published snow guidance: ~5–6 psi hardpack, 3–5 packed, 2–4 soft, 1–2 deep.
// Safety — the part that can never be overridden
The ISO blow-off test only holds 110% of max pressure for 5 minutes. The margin is thin — so a cap always beats the model, and it’s applied last where nothing downstream can raise it.
// Worked examples
A starting point for a range of riders and setups. Try your own in the live tool — it takes seconds and needs no sign-in.
| Rider and setup | Front / Rear (psi) |
|---|---|
| Road 28 mm, smooth, 170 lb, hooked 21 mm rim | 63 / 66 |
| Road 25 mm, smooth, 225 lb, rim “Not sure” | 72 / 72 (held at hookless limit) |
| Road 32 mm, rough pavement, 170 lb | 48 / 51 |
| Gravel 40 mm, mixed gravel, 170 lb, 25 mm rim | 33 / 35 |
| Gravel 45 mm, loose gravel, 150 lb | 23 / 24 |
| Gravel 40 mm, hardpack, 225 lb | 44 / 47 |
| MTB 2.4 in, trail, 170 lb, 30 mm rim | 18 / 20 |
| MTB 2.4 in, trail, 230 lb | 23 / 25 |
| Plus 2.8 in, trail, 170 lb, 40 mm rim | 15 / 16 |
| Fat 4.5 in, groomed snow, 170 lb | ~6 / 6 |
| Fat 4.8 in, soft snow, 170 lb | ~3 / 4 |
| Fat 4.8 in, deep snow, 170 lb | ~2 / 2 |
Whole psi, with half-psi steps under 10. Units follow your setting.
// What we’re honest about
hard rule Physics and standards — the gas law, ETRTO caps, ISO minimums — are absolute.
measured Surface, width and load come from measured, published data.
product choice Wet, casing, riding style, inserts and tubeless offsets have little or no measured data anywhere. So they mainly move the safety floor, not the headline number — and we label them as choices, not science.
No rider weight is stored. No sign-in is needed to use the calculator.
// It gets better with riders
The model is versioned. Exactly one version is active at a time, and new data only changes results when a new version is reviewed and switched on. The safety caps are fixed rules, not model parameters — so new data can never loosen them.
Coming: riders will be able to log the pressure they actually ran, how it felt, and whether they flatted. Over time that becomes an open, real-world dataset across road, gravel, MTB and fat — improving the model exactly where published data is thinnest.
// In the app
In the Megylla app for iPhone and Android, every bike page has a tire icon — one tap opens the calculator already set up for that bike. It’s also under Settings › Tire Pressure Calc.
The same calculation runs on the web, iOS and Android, so your results never disagree.
// FAQ
Published charts disagree widely for the same rider, and gauges vary 5–6%. Ours is a calibrated starting point, with the reasons shown so you can judge it yourself.
A tire, rim or hookless limit applied. The result tells you which one, and that your weight would call for more. Consider a wider tire.
Leave it as “Not sure.” We apply the safer hookless limit, and tell you that’s why.
No change on pavement. Off-road, tubes get about 11% more pressure and a higher floor to resist pinch flats.
Set pressure at riding temperature. Pressure drops about 2.5 psi per 10 °C at road pressures, and much more in proportion at fat-bike pressures.
Rider weight isn’t stored, and no sign-in is needed.
// Try it
Free, no sign-in, no email — and every number explained. Road, gravel, mountain, plus and fat.
Open the calculator →