I have just finished my first fixie conversion and have a question or two on chain noise.
I am running a 3/32 drive train with a 1/8 (temporary) chain. The chain line is within a millimeter or so of being straight. I have tightened the chain so that the cranks spin without catching but there is minimal droop in the chain between cassette and sprockets.
While riding there is a little bit of general noise in the drivetrain which I expected with the different size chain.
The problem I noticed is when going downhill at very high crank rpms (150 ish). Everything is fine untill I hit the point where my legs are just keeping up with the cranks and the chain is essentially slack. When I hit a bump like this, I suddenly get a rather large grinding noise from the drivetrain. This scared the crap out of me the first time, as I though I had thrown the chain and was about to get personal with the pavement. When I stopped and checked the bike the chain tension all looked fine and there seems like there is nowhere near enough slack to throw it off.
My questions basically are: Is this sort of thing normal and anything to worry about? Is +/- 1mm an accurate enough chainline to prevent throwing the chain? Should the chain be as tight as physically possible before it interferes with the chainring turning or just tight enough so the chain cannot come off?
I have really enjoyed the first few rides on the fixie and will join one of the brisbane rides soon.