Originally Posted by
PoorInRichfield
Is it enough resistance to matter on one ride? Not likely. How about 1,000 rides? Well if I had a dollar for every wasted watt...
Wattage is energy-per-time. It doesn't change by riding for more time. If your freewheel is costing you a watt, and you had a dollar for every wasted watt, you'd have a dollar whether you rode your bike 20 feet or 3,000,000 miles.
An unbalanced wheel is wasting energy. If it wasn't, they wouldn't bother balancing things like flywheels.
They balance flywheels because an imbalanced engine doesn't work fluidly. The big issue isn't that an imbalanced spinning mass loses energy in and of itself, it's that the spinning mass in question needs to be balanced in order to do its job of keeping everything else moving fluidly relative to each other. An imbalanced engine setup can produce noticeable noises and vibrations from all throughout the drivetrain, cause components to wear rapidly, and in extreme cases, the fatigue can even lead to devastating crankshaft failure.
One can get a massively heavy wheel to rotate with very little effort... if it's balanced. Most of the wheel balance deniers focus on not being able to feel an unbalanced wheel, which isn't really the point. The issue is that an unbalanced wheel is wasting energy... not only once the wheel is rotating but in just getting the wheel to rotate in the first place. Sure, there isn't enough force being generated for a 175 lbs rider to be able to feel it when sitting on the bike, but none-the-less, there is a loss of energy and the force certainly can be noticed when spinning an unbalanced wheel when not sitting on the bike. If I can reduce this loss for effort and little cost in conjunction with other small gains, that is what marginal gains is all about.
On a fundamental physics level, balance has basically zero effect on the amount of energy required to bring a rotating mass of a given rotational inertia to a certain rotational velocity.
Where it can have an effect is if the lack of rotational smoothness is causing other elements of the system to interact unsmoothly with each other. That's why there's the emphasis on detectable things throughout the bike+rider system; if the wheel is moving stably relative to the ground and the frame is moving stably relative to the wheel, it's hard to imagine where any losses would be coming from.
A wheel imbalance should theoretically cause a slight oscillation in the loading at the wheel, which could cause a vertical oscillation in the system, but the expected magnitude of this effect is
extremely tiny.