Setting bike tire pressure by rider weight, not the sidewall

Tire pressure trades off rolling resistance, comfort, grip, and pinch-flat protection. Too high and the tire bounces over road texture instead of conforming to it — that bouncing is energy loss and the wheel is briefly not in contact with the road, which is when you lose traction. Too low and the casing folds under load, the tire squirms in corners, and you risk pinching the tube against the rim on impacts.

The sweet spot moves with weight

A rough rule for 25 mm road tires with tubes: front psi ≈ (rider + bike weight in lb) × 0.4, rear psi ≈ same × 0.5, front biased about 10% lower than rear because more weight sits on the rear. For a 180 lb rider on a 20 lb bike (200 lb total): front ~80 psi, rear ~100 psi. On 28 mm tires drop about 10 psi. On 32 mm drop another 10.

Tubeless changes everything

Without a tube, pinch flats stop being the limit — you can run 15-20 psi lower before the tire starts squirming. A 28 mm tubeless tire that felt right at 85 psi with tubes will feel better at 65-70 tubeless. Gravel tires 40 mm+ live in the 25-40 psi range depending on rider weight.

Metric

1 bar = 14.5 psi. 100 psi = 6.9 bar. European pressure gauges and floor pumps usually show both. The 'right' number is the same in either unit — pick the scale your pump reads best.

Recap

Sidewall max is a ceiling. Real pressure is a function of your weight and your tire width. Start lower than you think, especially on wider or tubeless tires.