Chain length question
Ok, so I recently updated to a flip flop track hub and have been riding exclusively fixed, b/c freewheel is an 18T and fixed is a 14T, so I have to mess around w/ two masterlinks to get the right chain length when switching. I love riding fixed, but would like the option (if i'm dying on a ride, or simply for different gearing) to be able to flip to the free. I have an 80s univega in awesome condition, and it seems like I would have about 1/2" of room to adjust the axle fore/aft. Can anyone tell me what the max. tooth difference can be b/w the fixed/ free. I know that between the 14T fixed and the 18T free there is a 1" chain length disparity, and one tooth of cog usually adds 1/8", but it just doesn't seem to add up (b/c of the width of freewheel?) Right now I have the fixed on, and easily have 1/2" to move to the rear, so on paper I would think that the 18T would require 1/2" extra chain, and so if I replaced one of the master link sections with a half link I should be able to run both cogs with the same chain?
If all that was too confusing, all I want to do is have the fixed and free both using the same chain, using fore/aft axle movement to make them both fit in the dropouts. SB says a 1T to 2T difference, would running a 16T fixed solve all this?