Hey gang. I've been pestering a guy at work (MTB and road bike background, much better cyclist than me) with a flip/flop hub riding around on the SS side to try the FG side. Yesterday he told me he had tried it for a few days and liked it but switched back because he had a really disconcerting slippage problem.
The way he described it was that he was practicing skids in the parking lot, and all of a sudden the cog seemed to slip on the hub as he was applying the back pressure, so he had no braking through the pedals. Apparently once he tried pedalling again he was able to apply drive to the cog, and was able to brake through the pedals again. Then some time later he had the same slippage problem under acceleration, said he dropped down to 6:00 so fast that he almost smashed his face into the bars.
To me it sounds like the chain jumping on the chainring and/or cog, but he said there was none of the noise you'd associate with that happening, that it just felt smooth when it let go. Also, his chain should have had the right tension because he had just flipped the hub a few days before - there's no way it would have worn enough to start jumping in that short time. And he's never had this issue on the SS side under acceleration, so it seems he knows how to maintain a chain just fine.
Any thoughts on what could cause such a thing? I would expect that as soon as you get a bit of slippage, it's a symptom of the threads being stripped - which would mean pretty much immediate failure - not intermittent like he saw. But what else is there to go wrong on a FG hub? Not much!