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.
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.