Every climb page gives a time to the top at 2, 3, 4 and 5 W/kg. The physics is the same for every climb: how fast a steady effort carries a rider up that road, stretch by stretch. Here is exactly what goes into it, and what doesn't.
The estimate is for a 70 kg rider on a 8 kg bike holding the same power from the bottom to the top. W/kg counts the rider alone, so 3 W/kg is 210 W. We don't know your weight or your FTP, so the figure is the same for everyone who opens the page.
We take the climb's elevation profile, the one corrected for mapped tunnels, and cut it into 100 m stretches: shorter ones would chase noise in the elevation data. A stretch that looks like an unreported tunnel (a hump the road never climbs) is replaced by a straight line between its ends, so it can't add phantom minutes.
On each stretch three forces hold the bike back: gravity on the slope, the tyres' rolling resistance, and air drag. The first two depend on the grade. Drag grows with the square of the speed and falls with altitude: at 2,000 m the air is about 21% thinner than at sea level.
P = ( m·g·(sin θ + Crr·cos θ) + ½·CdA·ρ·v² ) · v
97% of the rider's power reaches the road; the rest is lost in the drivetrain. We find the speed at which the forces above use exactly that power, and divide the stretch's length by it. Add up every stretch and you have the time to the top.
The same calculation on a road of one steady gradient, so you can set the estimate against your own rides: our 70 kg rider at 1,000 m, no wind. Speeds in km/h.
| Gradient | 2 W/kg | 3 W/kg | 4 W/kg | 5 W/kg |
|---|---|---|---|---|
| 0% | 30.8 | 35.9 | 39.9 | 43.3 |
| 2% | 20.4 | 26.4 | 31.1 | 35.0 |
| 4% | 13.5 | 19.0 | 23.7 | 27.8 |
| 6% | 9.7 | 14.2 | 18.3 | 22.1 |
| 8% | 7.5 | 11.2 | 14.6 | 17.9 |
| 10% | 6.1 | 9.1 | 12.1 | 14.9 |
| 12% | 5.2 | 7.7 | 10.2 | 12.7 |
| 14% | 4.5 | 6.7 | 8.9 | 11.0 |
Spotted a time that doesn't add up? Contact us