Tight/loose spots in chain when cycling crank
I'm sure this has been discussed before ad nausea but here goes...
I've read that a tight/loose chain is not necessarily a problem unless the chain falls off. Always tighten the chain to the tightest spot so that the chain isn't too tight. Ok, so I do all of that but what actually causes this?
I'm guessing variances in the chain ring and/or crank arms? Maybe the crank and chain ring are not quite 100% concentric. Maybe the sprocket is a little out of round also, but I wouldn't think this would cause quite as much as a crank that is out.
Anyone care to weigh-in on this with wisdom on what the cause(s) are and any Pro tips?