scaredypants – Member
It’s an odd thing that you can ride into really quite fast winds, since supposedly almost all your effort is to overcome wind resistance
There’s a clever explanation, isn’t there ?
The difference between “power” and “tractive effort” !!!
The power a human can output is limited, to something round about 400Watts, depending on how fit you are.
But the tractive effort, or the FORCE you can push a bike forward with is pretty much unlimited, assuming you have low enough gears.
And as Power = Force x speed, for a given power, as speed rises the force you can produce at that level of power falls inversely.
So, if 400w is enough to do lets say 20mph, the tractive effort you are generating at that speed is 44.7N. So, if your speed is constant, then we know the 20mph head wind (ignoring other rolling frictional losses) is pushing back at you with the same force (44.7N)
Halve your speed, to 10mph, and your same 400w output gives you double the tractive effort (89N). So at this new speed, the same 20mph head wind is only now using up 200W, leaving you with 200W to propel yourself along (which is the power needed in our example to go 10mph)
So, basically, headwinds of a given speed require you to halve your previous speed. ie, if you could do 20mph without a headwind, a 20mph headwind means you can do 10mph, and a 40mph headwind gives you the capability for just 5mph…….