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When you're climbing a steep hill you have very little momentum. Which is why it feels very different to the same Power output on the flat. So you constantly accelerate Your Wheels.
Seeing the pros use very low profil Wheels, on mountain stages, when their bikes are struggling to make the legal weight With semi deep rims. Is a good indication of this.
Smallfurry-
The internet seems to disagree with that:
http://www.reddit.com/r/Velo/comments/29oedw/the_case_against_rotating_weight/
https://van.physics.illinois.edu/qa/listing.php?id=7559
Yes, the wheel weight counts more than the frame weight. The reaon is that when you accelerate the bike everything moves forward together but the wheels also rotate. The average velocity over the whole wheel is the same as the rest of the bike, because the different parts move all the different directions in a circle. however, energy goes as the square of the velocity, and the rotational energy of the wheel just adds to the energy of the average motion. So you have to pump more energy into the bike to get a pound of wheel moving than to get a pound of frame moving. If all the weight of the wheel were out at the rim (which isn’t too far from true) the total wheel energy per pound would be twice the frame energy per pound, i.e. equal rotational and static weight. The real rotational number would be a little less.
Of course if you’re going uphill, the extra work to lift the bike against gravity only depends on the ordinary weight, not how it’s distributed.
fizzy.bleach
But isn't that only when accelerating? #notaphysicist