I actually thought I should say something about biopace after reading the OP, firstly to be funny (and yeah, I do find it funny) and secondly because they actually do work on fixies, as counterintuitive as it seems.
In my experience, making sure the chainring is centered on the crank spindle is the biggest deal. I've had to carefully work on this with two bikes - because there is some play when you mount a chainring on a crankarm, before you tighten it down. And this can place teeth on one side further away from the axis of rotation.
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"c" is not a unit that measures tire width