well i ran into a new campagnolo 39t ring for $15 so i bought it to give me a second gearing option. in the process i discovered and interesting setup. i fully expect that some may laugh:
now for the explication. my rear hub is a white industries eno.
fixed chain line = 43mm
ss chain line = 47.4mm
this gives me a 42x16 fixed for road riding and a 39x18 for cross riding and a close chain length for each. funny looking yes, but great flexibility for $15