Originally Posted by makeinu
I think you guys are getting distacted. Obivously energy is always conserved. Apart from certain loss processes (drag, friction, etc) energy will always remain within the system.
However, the body is primarily restricted by the power it can deliver, not the energy. It doesn't take any more energy to move an elephant up and down a ladder than it does a paperclip (zero in both cases), but your body will waste a lot of energy in order to muster the necessary power to move the elephant.
Furthermore, it's better to retain control over acceleration/deceleration with your legs. If you invest energy in getting a large wheel up to speed then you risk losing that energy if you need to brake, but if you keep the energy in your muscles then you don't risk as much. On average the higher risk should translate to more energy lost due to braking.
Uh, sorry, but you don't seem to be clear on energy, power, or the realtionship between them.
To move a mass M, up a ladder, increasing it's height by h, in a gravitational field with gravitaional acceleration g, will take energy M*g*h. So, if an elephant is a mass M and a paperclip is mass m, then the difference in energy required would be (M-m)*g*h.
Power is energy per unit time. It is the rate of energy delivered, or extracted from a system. You are right in that a rider will be limited in how much energy he can deliver per unit time. His power does have some finite limit.
Braking is an issue. In the other discussions I was arguing that in near steady state, you get the energy out of the system, in overcoming drag and friction, that you put in. If you hit the brakes, then all that energy goes to heat. But remember, hitting the brakes you give up kinetic energy from ALL sources. That includes the translational kinetic energy. The translational kinetic energy of a 150 pound biker on a 25 pound bike dwarfs the rotational kinetic energy in the rotating wheels. If you are doing nothing but start and stop, your wheels are a small part of your worries!
Speedo