Since there's very little mass involved in a free spinning drive train, small differences will have an exaggerated effect. But th results can be deceiving. For example a heavier rear wheel will spin longer than a light one. Even small tire weight differences will show up, so what seems like high friction might simply be low weight.
Also, chain tension, age and lube will make a difference, especially if there's excess tension.
So as posted above, unloaded spin tests are just about meaningless. That doesn't mean that a fine old bike isn't a fine old bike, just that the claim can't be based on this test.
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