Originally Posted by WhyFi

Bull****tery aside for the moment, I have a not-at-all-thought-out theory that a lot of the sensation of increased speed and nimbleness that many associate with lighters wheels (rims/tires particularly) is because of a diminished gyroscopic effect - this could mean less effort when leaning the bike over in a turn or flicking side-to-side (when sprinting, for instance). This may explain the divide between riders that report a much easier 'spin up' effort and those that are dismissive because of calculations that show spin-up power differences (of a static wheel) that would likely be imperceptible to the rider.