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When coasting (not pedaling) downhill, do single speed bikes tend to be faster than multi speed bikes? Assume that both types are road bikes with similar frame, tires, etc.

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    Single speed (that can coast) or fixed speed (where the pedals rotate at road speed all the time) ? – Criggie Jul 09 '16 at 21:12

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The two differences will be that the multispeed bike has more air resistance from the drivetrain and the comparison of resistance between the ratchet in the single speed bike and the freewheel or freehub on the multispeed. Both effects are rather small. The rider/bike aerodynamics will dominate.

Ross Millikan
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    I would love to see some lab results for that theoretical difference. – mattnz Jul 09 '16 at 20:31
  • @mattnz: There are plots, some on this site, showing the power loss due to air drag and rolling resistance as a function of speed. Air drag dominates. If you think about the frontal area the drivetrain difference represents, it has to be a small component of the air drag. – Ross Millikan Jul 09 '16 at 20:35
  • I would doubt that the derailers contribute enough wind resistance to be measurable in real life circumstances. The drag from a fixie's pedals always turning would almost certainly be greater. – Daniel R Hicks Jul 09 '16 at 21:24
  • @Daniel The OP says single speed and coasting, not fixie. – andy256 Jul 10 '16 at 01:46
  • @andy256 - But it's not clear what he means by "coasting". He could be simply taking his feet off the pedals. – Daniel R Hicks Jul 10 '16 at 01:48