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Chain line: How close is close enough?…(3 posts)

Chain line: How close is close enough?…TFerguson
Dec 10, 2002 4:11 PM
Since perfect is non-existent, how close does the chain line need to be? 1 mm? 1 cm? As close as measurable?

re: Chain line: How close is close enough?…fixedgearhead
Dec 10, 2002 4:34 PM
You should be able to look down the chain line from the rear of the bike and see no perceptable deviation from straight as the chain comes off the chainring or off the cog. This is close enough for government work. If you want to get real finicky, then do the measurement from the center of the bottom bracket to the center of the chainring and center of the hub spacing to the center of the cog.
Sighting down the chainring is close enough, imho.

re: Chain line: How close is close enough?…xxl
Dec 13, 2002 2:30 PM
If you wanna get sort of accurate, you can put a metal (i.e., nonflexing) ruler against the side of your cog, and chainring, and view your bike from above. The ruler should look parallel to the rear tire, top tube, etc.

Really, though, unless you're unusually astigmatic, eyeballing it works fine. Much more important for FG is keeping the chain tensioned.