Bike tire pressure calculator

How the calculator picks a pressure

There is no single correct pressure, but there is a well-tested starting point. Frank Berto measured how far dozens of tires squash under load and charted the pressure that gives a 15% tire drop: the tire’s height shrinks by 15% when you sit on the bike. Bicycle Quarterly printed his chart in Jan Heine’s article “Optimizing Your Tire Pressure for Your Weight”, after finding that the pressure where its own tire tests stopped getting faster corresponded roughly to that 15% drop. Higher pressures made the bike no faster, only harsher. The 15% figure itself is the drop several tire makers recommended.

The chart works per wheel, not per bike. Your rear wheel carries more of the load than the front, so it needs more air. Bicycle Quarterly measured typical splits: a racing bike carries about 40% on the front and 60% on the rear, a randonneur bike with a front bag 45/55, and a city bike with a loaded rear rack 35/65. The calculator multiplies your total weight (you, the bike and anything you carry) by your split to get each wheel’s load, then reads Berto’s line for your width. For widths between the chart’s lines (20, 23, 25, 28, 32 and 37 mm) it reads between the two nearest lines.

Quick reference: road tires, 40/60 split

Front / rear psi from Berto’s chart for a road bike. “≤” marks a wheel lighter than the chart’s lowest load, so the chart’s edge value is the most you need.

Front and rear pressure in psi by total weight and tire width, from Berto's chart, 40/60 split

Rider + bike	700×25c	700×28c	700×32c
60 kg (132 lb)	≤48 / 68	≤42 / 58	≤33 / 45
70 kg (154 lb)	50 / 80	44 / 68	35 / 53
80 kg (176 lb)	59 / 93	51 / 79	40 / 61
90 kg (198 lb)	68 / 106	58 / 89	45 / 69
100 kg (220 lb)	76 / 119	65 / 99	51 / 77
110 kg (243 lb)	85 / 132	72 / 110	56 / 85

Gravel tire pressure

Berto’s chart stops at 37 mm. For gravel the calculator switches to Michelin’s published gravel and cyclocross table, which gives one pressure for both tires by rider weight band, for 33, 35, 40 and 47 mm tires. A 71–80 kg rider on 40 mm tires starts at 3.0 bar (43.5 psi); on 47 mm tires, 2.4 bar (34.8 psi). Michelin notes that rougher terrain calls for slightly lower pressure within the recommended range, and that tubeless setups can run lower because there is no inner tube to pinch. Bicycle Quarterly makes the same point from its testing: on gravel you can run lower pressures than on pavement. If you ride 38–47 mm tires on smooth roads, the calculator still uses Michelin’s table (the nearest published chart) and says so.

The maximum is a hard limit

Every tire has a maximum pressure moulded on the sidewall, and some rims have one too. The calculator never suggests more than the lower of the two, and tells you when the chart wanted more. That usually means the tire is too narrow for the load, and a wider tire is the fix, as Bicycle Quarterly also advises for heavy riders and bikes.

Hookless rims (tubeless straight-side, “TSS” in the ETRTO standard) hold the tire without a hooked lip, so they have low pressure limits that depend on the tire. Schwalbe, which requires rims built to the ETRTO hookless standard, publishes these maximums for its tubeless tires on hookless rims: 5 bar (72 psi) for 25–29 mm, 4.5 bar (65 psi) for 30–34 mm, 4 bar (58 psi) for 35–39 mm, 3.5 bar for 40–44 mm and 3 bar for 45–54 mm. Continental prints the hookless maximum on the tire’s packaging and says never to exceed it. Tick the hookless box and the calculator caps at 5 bar (72.5 psi), or at Schwalbe’s lower figure for wider tires. If your tire’s own hookless figure is lower still, enter it as the tire maximum.

Cold mornings and hot days

Air pressure follows temperature. Continental gives a rule of thumb of about 0.17 bar (2.5 psi) for every 10 °C (18 °F) of change. Pump to 84 psi in a 20 °C hallway, ride out at 2 °C, and the tire is about 4.5 psi softer than you think. That is why the card has the optional “pumped at / riding at” boxes. On a frosty December commute, check the pressure outside or top up a little indoors, staying under the maximum. On a hot summer day the opposite happens, so never pump to the maximum in the cold.

Fine-tune by feel

1. Set the calculated front and rear pressure with a gauge you trust, and note which gauge it was: pumps don’t always agree.
2. Ride a familiar loop with some rough patches. If the bike skips sideways over bumps or the ride buzzes through your hands, let a little air out.
3. If the tire feels vague when cornering, squirms, or (with tubes) you feel the rim touch on a sharp edge, add air.
4. Change one wheel at a time by a couple of psi, and write down what you liked. Bicycle Quarterly’s own advice is short: when in doubt, let out some air.

Common mistakes

• Using your body weight alone. The bike, bottles, bags and a winter jacket count too.
• Same pressure front and rear. With a 40/60 split the front needs noticeably less.
• Pumping to the sidewall maximum. It’s a safety limit, not a target. Bicycle Quarterly found that maximum-pressure habits under-inflate narrow tires and over-inflate wide ones.
• Forgetting the rim. A hookless rim, or a rim with its own maximum, can be the real limit.
• Trusting the label width. A “28” can measure 26 to 30 mm depending on the rim. If yours measures wider, enter the measured width.

Heavier load for a tour? Check your chain wear and gearing before you go. If your ride includes a hike-a-bike section, Summit Cabin estimates the walking time.