Tire pressure calculator
The fastest pressure isn't the highest one. Above a surface-dependent breakpoint, vibration losses eat everything a harder tire promises — so the right pressure depends on your weight, your real tire width, and the road. Dial it in, front and rear.
⚖️ SYSTEM WEIGHT Everything the tires carry: you in race kit, the bike, bottles, and anything bolted on. Pressure scales directly with load — this is the single biggest input, so guessing 5 kg low costs you roughly 0.3 bar. Your body mass is shared with your athlete profile, so it stays in step with the rest of the site.
SYSTEM WEIGHT 85.0kg synced with your athlete profile
🚴 POSITION How your weight splits front to rear. In the aerobars you sit further forward — 48% front — so the front tire carries more than on a road bike (45%). That's why the two wheels get different pressures.
📏 TIRE WIDTH The real mounted width, not the number on the sidewall — a 28 mm tire measures well over 28 mm on a wide modern rim. Width dominates the result (pressure falls as width^1.5), so measure with calipers if you can. Otherwise give the nominal size plus your rim's inner width and it gets estimated.
🛣️ SURFACE The impedance correction. Past a surface-dependent breakpoint, a harder tire stops rolling faster and starts vibrating you and the bike — losses go back up. The rougher the road, the lower that breakpoint sits, so rough surfaces get less pressure, not more.
💨 SPEED Your realistic average for this course. Faster riding hits bumps harder and pushes the breakpoint up a little, so it earns a small pressure bump (±3% at the extremes). A minor adjustment next to weight and width.
🔧 SYSTEM Tubeless has no inner tube to squirm and pinch, so it runs ~0.3 bar lower than a tubed setup. Casing matters too: a supple high-TPI tire deflects more at the same pressure and wants a touch more air; a reinforced or puncture-belted casing is stiffer and wants a touch less.
Casing
🧰 PRESSURE LIMITS (OPTIONAL) The max pressures printed on your tire sidewall and stated by your rim maker. Whichever is lower wins, and it always overrides the recommendation — a computed pressure your rim can't take is not a pressure you ride.
The lower of the two always wins over the recommendation.
Scientific basis & sources
The calculator is based on Frank Berto's 15% tire-drop model and the publicly published impedance/breakpoint research of Tom Anhalt and Josh Poertner. The hookless limit follows ETRTO (5.0 bar / 72.5 psi). Full derivation and calibration notes live in the project's formula documentation.
- — All About Tire Inflation 15% tire-drop model, load/width curves, weight distribution
- — Bicycle Tire Pressure (open Berto fit, 2013) Fit P ∝ load / width^1.5 (basis of the calibration parameters)
- — Optimizing Your Tire Pressure for Your Weight Wheel-load split and application of the Berto charts
- — Tire Pressure Take-Home Limits of the drop model, influence of the casing
- — Part 4A: Rolling Resistance (History and Previous Works) Impedance concept (losses from surface roughness)
- — Part 4B: Rolling Resistance and Impedance Breakpoint logic: surface/speed correction
- — Field measurements of the breakpoint pressure (Blather 'bout Bikes) Original empirical discovery of the breakpoint
- — Talking Tire Pressure for Zipp Wheels Practical anchor for the surface correction, hookless context
- — Standard for hookless (TSS) rims Hard limit 5.0 bar / 72.5 psi