Originally Posted by
bbattle
Older frames with long dropouts have plenty of room for 4 or 5 tooth difference. You'll rarely ever want such a spread in real life. Maybe 2 tooth difference.
Formula fixed/fixed hub with 16/18 Surly Dingle and 16T freewheel. Yes, freewheel cog fits nicely on the hub. If you look closely, you can see an old bottom bracket lockring I put on the hub first as a spacer.
Looks like you should drop a link. You can't move the wheel any farther back in the dropout, and you'd need to if you wanted to use the smaller cog.