Quote from: Wothill on November 28, 2011, 10:22:03 pmQuote from: Tigerbiten on November 26, 2011, 08:39:44 amWind resistance goes up at square of the speed.Power needed to go at that speed goes up at the cube.Hang on. I agree with the first: wind resistance is proportional to the square of the speed, but the second surely contradicts that. How could you measure wind resistance other than in units of power? Or did I miss a step in the logic?Wind resistance is a force - you can measure it in lbs or Kg, but purists would use Newtons.To get the power required to maintain that force you need to bring time and distance into it, as there's clearly no way that you can sustain the speed that you just calculated the wind resistance for if the force you can generate is at a lower speed (the force you can generate at the driven wheel is a product of engine torque (rider strength) x gear ratio). Sheldon Brown's "gain ratio" is useful for working that out, since it can directly translate leg strength to tractive effort.You have to multiply by the speed again to get the power figure from the torque, thus increasing from the square to the cube.

Quote from: Tigerbiten on November 26, 2011, 08:39:44 amWind resistance goes up at square of the speed.Power needed to go at that speed goes up at the cube.Hang on. I agree with the first: wind resistance is proportional to the square of the speed, but the second surely contradicts that. How could you measure wind resistance other than in units of power? Or did I miss a step in the logic?

Wind resistance goes up at square of the speed.Power needed to go at that speed goes up at the cube.