Does it matter how far backwards you can spin your drivetrain? If I spun my cranks backwards on all my previous bikes I would get a good few spins out of them, maybe as many as three or four on one of the bikes. But with my current road bike I can barely get a full rotation out of it.
Does this matter? Is it an indication of the friction within the drivetrain, or just the way that some setups work, either by design or as a side-effect of how they're designed?
I'm guessing that it's the rear hub that slows it down, but there's no restriction in speed when riding fast or freewheeling that I can detect, and no excessive noise. It was an almost brand new Cannondale Optimo and the BB has been serviced.
I don’t think it’s a good indicator. Plenty of viscous lube and lightweight (-&gt; low inertia) components can easily mean that a high end bike spins worse than a 20 year old bike with dry and rusty bearings.
The most important thing is friction under load, which is hard to measure. But you should make sure that bearings spin with little force (to make sure they don’t have excessive preload), that they don’t have any play and that they turn smoothly through the full 360°.
To check if the hub’s free wheel mechanism has excessive friction, spin the rear wheel. If you have quick release axles, make sure they are not excessively tight. To check if it’s the bottom bracket bearings (more likely) take off the chain and spin the cranks. If it’s neither of them it has to be the rear derailleur.