Enter your power, weight and the gradient — see instantly which gears are achievable and how fast you'll go.
Power model — watts required = gravity + rolling resistance + aerodynamic drag, all multiplied by speed. This is the standard cycling physics model.
Green gears are comfortably within your power. Amber gears are within 15% of your limit — hard but possible. Red gears need more watts than you've set.
CdA is your drag coefficient × frontal area. Hoods ≈ 0.36, drops ≈ 0.32, TT position ≈ 0.22. It has less effect on climbs than on flat roads.
System weight — include rider, clothing, shoes, bike, water and food. Every kilogram matters on a climb.
VAM (velocità ascensionale media) is vertical metres climbed per hour — the classic climber's metric. Pro riders hit 1,500–1,800 m/hr on steep mountain stages.
Crank length affects leverage, not speed. Shorter cranks (e.g. 170mm) spin more freely but reduce torque per pedal stroke — the equivalent chainring shows what size would give the same leverage on a 172.5mm reference.