体重、自転車重量、勾配、路面の種類、風を考慮し、パワー（ワット）から走行速度を物理計算で推定。現実的な転がり抵抗とCdAのプリセット付き。
| 力の内訳 | ワット | 全体に占める割合 |
|---|
総パワー = 転がり抵抗 + 空気抵抗 + 重力 + 駆動系ロス。具体的には: P = Crr・m・g・v ＋ ½・ρ・CdA・(v + 風速)²・v ＋ m・g・sin(atan(勾配))・v を、駆動系効率0.95で割った値です。
定数: 空気密度 ρ = 1.225kg/m³、g = 9.8067m/s²。速度は二分探索で求めます。
The tool inverts the standard cycling power equation. Power at the pedals is (Crr·m·g·v + ½·ρ·CdA·(v+wind)²·v + m·g·sin(atan(grade/100))·v) ÷ 0.95, with air density ρ = 1.225 kg/m³, gravity g = 9.8067 m/s² and a 0.95 drivetrain efficiency. That cannot be rearranged for v algebraically, so it runs sixty rounds of binary search between −20 and 30 m/s to find the speed your wattage actually produces.
Surface / bike sets the aerodynamic and rolling constants together: Road bike CdA 0.32 and Crr 0.005, TT bike 0.24 / 0.004, Gravel 0.36 / 0.012, MTB 0.42 / 0.020, Commuter 0.45 / 0.008. On the flat CdA dominates — at the default 75 kg rider, 8 kg bike and 200 W the breakdown shows aerodynamic drag taking about 80% of your power. Tilt the Gradient field to 5% and gravity takes 85% instead.
Fixed CdA presets are the weak point. Your real frontal area swings enormously between hoods, drops and a tuck, and 0.32 describes a moderately aggressive road position rather than any specific rider, with no field to enter a measured value. Air density is pinned at sea level, so mountain speeds read low. Wind is a pure head- or tailwind with no crosswind or yaw angle, and drafting is not modelled at all.
About 33 km/h for a 75 kg rider on an 8 kg road bike in still air, which is the default setup. Aerodynamic drag takes roughly 80% of that power, so the same wattage on the TT bike preset buys nearly 37 km/h.
Because gravity scales with total mass and speed. At 83 kg combined the climbing term absorbs about 85% of 200 W, dropping speed to roughly 14 km/h — under half the flat figure — while aerodynamic drag falls below 7% of the total.
The Road bike option uses a single CdA of 0.32, roughly a moderately aggressive hoods position. Real riders span about 0.28 in the drops to 0.40 sitting upright, and there is no custom field, so pick whichever surface preset is closest to your posture.
No. The model treats you as riding alone in still or steady air. Sitting in a bunch can cut aerodynamic drag by 30% or more, so real group speeds at a given wattage will always run higher than this estimate suggests.
On the flat, almost none — mass only enters through rolling resistance, a small share of total power. On a climb it is close to proportional, because the gravity term is multiplied directly by rider weight plus bike weight combined.
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