Re: To tension or not to tension, that is the question?
I run my old Mesa Runner mountain bike without a tensioner. I had to modify the left side chain stay a bit to get enough clearance so the chain wouldn't touch. It works very well at least for the 200+ miles I've run it. As already mentioned you have to get your sprocket centered well or there will be some tightening and loosening of the chain as the wheel revolves. It only takes a few thousandths for this to happen. I've got a bit of variation in the chain tension as the wheel turns, it varies from about 1/8" slack to 1/2". That amount doesn't hurt. Checking the sprocket with a dial gauge shows a lack of concentricity of around .004". It doesn't take much. One other consideration is that I'm using a 15 speed bike if you're using a single or three speed setup it might be difficult to get the chains tensioned on both sides. It also helps if the dropouts are somewhat horizontal. I haven't had any axle creep at all so far. I did put star washers under both axle nuts.
Goldwing 1500, Silverwing 600, Schwinn 49