Bars are set slack right now, more comfort for trainer time.

Gearing is 50x17 (71") right now, I have a 55t front ring too (78.5"). It's on 650c wheels. I did that 17t rear because a brand new chain (like in the pic) just fits with a little slack and the rear hub forward. Gives me room for some stretch and no need for a 1/2 link. The 55t front fits pretty good too. If I was doing track time or racing a flatter course, I'd change the rear cog. For my purposes, the 71" and 78.5" combos work just fine.

Hub was made for me, it's a mountain bike hub (disc) so the cog is bolted in and the internals where machined custom.

Pic of the hub by its self.