Old 05-20-10, 10:33 PM
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Join Date: Mar 2006
Location: Vancouver, Canada
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Bikes: Rodriguez Shiftless street fixie with S&S couplers, Kuwahara tandem, Trek carbon, Dolan track

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OK, first some definitions: A bike chain consists of rollers held between inside links attached by rivets to outside links. So, chain measurement tools assume that all rollers are the same diameter. They also assume that the tool will be placed straight in the chain (perfectly parallel to the links). So problems in measurement could occur if the chain rollers are slightly smaller than they should be, or if the measurement tool is placed somewhat at an angle. There might also be some play within the roller. If there is the remotest possibiity of any of this, then your measurement will be out. I like measuring the top of the chain with some pressure on the pedals so the chain is taut, and with the tool pushed all the way against one side of the chain, or just measuring between two links with a ruler, but measuring the leftmost side of one rivet against the leftmost side of the other rivet 12 inches or away (not center of rivet to center, which is not as accurate because the center of the rivet is not usually marked). (Note that even if you live in a metric country, you still need to use a ruler graduated in Imperial inches because bicycle chains are all pitched at 1/2-inch.) And all pedals have a 9/16-inch bore. Go figure.

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