Originally Posted by
jrickards
I've read something similar although what I read was more in context of racing where it seems to be more beneficial to drop someone on the hills (it certainly would be from a psychological perspective), the effort in fact is disproportionate to the total speed gain. The author went on to say that if you're simply challenging yourself, conserve your energy going uphill and then put in the effort downhill and on the flats.
Anybody that says conserve on the uphill and put the effort into the downhill has it totally backwards.
If you're going fast (i.e. downhill) then more effort gives you only a marginal gain in speed because the effect of wind resistance above about 10 mph becomes more and more exponential. But when you're going slow (i.e. uphill) more effort gives you what's close to a proportionate increase in speed.
Downhill, double the effort and you might go 25% faster. Uphill, double the effort and you might go 90% faster. The specific gain/drag depends on the exact speeds and inclines involved. But this effect is undeniable.
These concepts relate directly to my training as an airplane pilot where we approached this a little more formally. At less than supersonic speeds, there are primarily only two components in wind drag. These are known as Parasite Drag and Form Drag (for airplanes there is also Induced Drag but that is not relevant to bicycles).
The form drag is caused by the compression of air molecules in front of a moving object. The object pushes the molecules directly in front of the object, those molecules then push on the molecules in front of them, and so on. So the object is not just pushing the air out of the way, the air in front of that air is getting pushed too, and so on to a diminishing extent as you move out in front of the object. The drag is caused by the energy required to compress the air in front of you. The faster you go, the more ALL the air in front of you is asking to be so-compressed before it gets out of your way. This gives the form drag an exponential effect, where the drag increases with the square of velocity.
Then there's parasite drag. Parasite drag is basically the friction of the air molecules as an object moves thru the air. Parasite drag is all over the object, not just in front of it. Parasite drag is proportional to the speed of the object.
So both of these types of drag are in play. But because the form drag is exponential, it becomes a stronger and stronger component of the drag as speed goes up. At low speeds, the parasite drag is much more significant. But the faster you go, the more the drag will seem to be only exponential in nature.
There's more slowing you down than just air resistance. So overall drag is not increasing as the square of speed necessarily. That's just what the form drag component of your overall drag is doing. But the faster you go, the less significant these other components become because they increase linearly instead of as the square of speed.