chain tension
 

okay, one more question. what is the proper chain tension for a fixed gear?

Enough so you can move the chain 1/4 to 1/2" up and down when you press on it lightly between the chainring and the cog. When you are motionless, there should not be much movement forward or backward in the cranks before the chain is engaged.

As tight as you can go without it binding. If you spin the cranks (and wheel) off the ground, there should be no binding, no brrruping, no fluttering in the chain. Often if it's too tight you'll feel it when pedaling, particularly at speed or under strain.

If at that point you got more than the 1/2" play, you need to recenter your chainring, get a new one, or accept that your chain is dangerously loose. (I play this last game on my rain bike which has thrown me before and may do so again.)

Tight enough so that you can't pull it off the chainring now matter how hard you try.

thanks for putting up with ignorance