So I'm this close to getting a specialized crossroads frame fully built up as a fixed gear, problem is the vertical dropouts. I found a 48-19 gearing to be very very close to right, the chain is just slightly slack. It seems fine riding around, but after a few bumps today the chain jumped off the cog.

Now, while the chain is slack, I don't see it being slack enough to accept a half link chain. I'd like to know, would going up one size in the cog (20t) make less of a difference in chain tension than a half link chain?

And I'm dead set on getting this thing to work. The frame has such a nice shape to it, it'd be a shame to give up on it.

I'd appreciate it if anyone could help! Thanks!