Originally Posted by
CACycling
I can tell you that when I swapped out tires and tubes on my commuter (from light-weight road tires and light tubes to kevlar-belted tires and thorn-resistant tube) I added well over 1/2 lb. to each wheel far away from the axle. It makes a huge difference in acceleration but minimal once I get it rolling (I have less than 10" of elevation gain on my entire commute). As I commuting involves a lot of stops and starts, it has a real impact. Not getting flats is worth it to me but you can not say that it does not impact "normal" riding.
Nope. Bike wheels simply don't weigh enough to matter. The upper bound on the rotational energy in a wheel is its translational energy. (it's less, since much of the mass isn't at the outside of the rim, but it's friday, so I'll leave out the calculus.). As we all remember, that energy is = 1/2 m*(v^2).
To accelerate a 5 kg wheel from 0 to 10 m/s (about 22 mph) requires an input of
1/2 * 5 kg * (10 m/s)^2 = 250 J.
To do the same thing to a 1 kg wheel
1/2 * 1 kg * (10m/s)^2 = 50 J
That's a difference of 200 J for a silly heavy wheel, and an incredibly light one. Bicycles have two wheels, so we've got 400 J difference. Those joules are spread out in time, of course. Top flight criterium racers can produce about 0.2 g of acceleration. That's 2 m/s/s acceleration, so five seconds. 80 watt power difference; you'd notice that, for sure. There aren't many bikes with 5 kg (11 pounds!) wheels, except for those with the special lead rim strip. Actual changes will be much less.
That 1/2 lb you added? call it half a kilogram for both wheels, and the change in energy is
1/2 * .5 kg * (10m/s)^2 = 25 J.
If you can accelerate in top crit racer style, it would require five watts for five seconds. More likely is that the power output would be (roughly) constant, and the time to reach speed would be slightly extended. The energy needed for the rest of the bike, assuming 100 kg rider + bike, is 5000 J (and it's actually quite a bit higher; that's only the inertial resistance, air resistance is going to be substantial at 10 m/s). 25 J of 5000 J is one half of one percent; that's below the resolution of many power meters; I'm sure it's below the resolution of your legs.
The drag you feel in those wheels isn't from their weight. It's from their increased rolling resistance, or the placebo effect, or the glue I secretly put on your tires every night.