WATTS AND SPEED
To calculatorsConverts watts to speed and vice versa according to honest physics: gravity, rolling, aerodynamics. It shows what the power is going on right now, and counts in seconds what will give a more aerodynamic landing, a light bike or other tires at your distance. The density of air is taken not from a constant, but from altitude and temperature.
Pedal power = (weight · g · sin(angle) + Crr · weight · g · cos(angle) + 0.5 · rho · CdA · air speed²) · speed / efficiency. Everything else on the page is a consequence of this formula.
Plus — counter wind, minus — tailwind. A minus slope is a descent. Altitude and temperature are needed only for air density, but at a speed of 40 + km / h they cost tens of watts.
The preset substitutes a typical value in the field next to it, then right with your hands — the calculator counts by the number in the field, not by the name of the preset. Gravel with pouches is aerodynamically more expensive than the upper grip on the highway, and loose gravel rolls four times worse than smooth asphalt.
Both fields are alive: enter the speed — you will see the watts, enter the watts — you will see the speed. The last modified field is considered set.
Bands are the proportion of each resistance in the current power. On the flat, aerodynamics eats up most of the watts and grows like a cube of speed; on the rise, gravity takes its place.
Two configurations for the same distance, the same slope and the same power. The difference is in seconds and in watts, which the loser would have to get.
Faster configuration A: winning 8:51 min:sec. Чтобы догнать её, B нужно ещё 21 Вт.
One change at a time, at the same power and at the entered distance. Base time unchanged — 3:20:00.
| Change | The result of the race | Speed |
|---|---|---|
| Minus 1 kg of the system | winning 22 seconds | 30.1 km/h |
| Minus 0.01 CdA | winning 1:34 min:sec | 30.2 km/h |
| Minus 0.001 Crr | winning 3:10 min:sec | 30.5 km/h |
| Headwind +5 km/h | loss 20:00 min:sec | 27.3 km/h |
| Height +1000 m | winning 6:36 min:sec | 31.0 km/h |
"Winning" — you will arrive earlier, "losing" — later. Compare not percentages, but seconds: they add up to the result in the protocol. The line about height is considered at the same power on the pedals: the air there is less frequent and the aerodynamics are cheaper, but it's harder to give out these watts at altitude — you won't really go 2000 m faster.
On a flat aero, weight is more important. The air resistance grows as the square of the speed, and the power to overcome it — as a cube. At 30-35 km/h on a straight line, this is already most of your watts, and the extra kilogram is almost invisible there: it only pays for rolling. Therefore, at the grader marathon, landing, helmet and clothing give more than the relief of the bike.
On the rise, the opposite is true. At 8% and 10-12 km/h, gravity takes almost all the power, and aerodynamics drops to a few watts. There, a kilogram is real seconds per kilometer, and the CdA almost does not solve it. Use the calculator to figure out both scenarios on your track: usually the race is divided into "flat, where you need to go aerodynamically" and "climbs, where you need to be light."
CdA is measured, not guessed. This is not a characteristic of the frame, but the area of the entire "rider plus bike plus luggage" system in a particular landing. The presets here are only an order of magnitude. The real number is obtained from a roll-out, from paired races on the same segment or in a pipe, and the difference between "thought 0.32" and "turned out to be 0.38" for a hundred kilometers is worth minutes.
The Crr of tires is different at times. Smooth asphalt and loose gravel differ fourfold, and two different gravel tires on the same surface — one and a half to two times. This is more than any difference between frames and wheels. The pressure, the frame and the width of the tire decide here: pick them up for the race coverage, not for the figure on the sidewall.
The calculator counts physics, not the race: it doesn't know about drafting, braking into turns, pushing the bike in the mud and your ability to keep power for three hours. Consider it the lower bound — the real numbers are always a little worse.