tire pressure
Front and rear starting pressures from your weight, your tires, and the trail you ride. Quick mode gets you a number in four taps. Full mode adds casing, bike weight, separate front and rear tires, and temperature.
Weight on each wheel
You plus the bike, split 46% front and 54% rear. The front gets a bit more than it carries standing still because braking and cornering load it up.
How much air the tire holds
A wider or taller tire needs less pressure to hold the same weight. Pressure falls a little faster than width rises, so a 2.6 runs about 2 psi under a 2.4.
Casing, tubes, inserts
A DH casing holds itself up, so it needs less air than a light one. Tubes need more air to avoid pinch flats. An insert protects the rim and lets you run a few psi lower.
Garage vs trail
A trail tire loses just under 1 psi for every 10°F it cools. Give both temperatures and we tell you what to set on the pump so you hit the number on the trail.
Checked against published starting points: about 22 front and 25 rear on a 29x2.4 tubeless trail tire for a 75 to 80 kg rider, 36 to 42 psi on 40mm gravel tires, and 5.5 to 7.5 psi on a 4.5" fat bike in mixed conditions. Terrain moves it from there. Wet and loose runs about 8% lower, bike park and hardpack 10 to 12% higher.