Old 11-20-15, 11:25 AM
A Roadie Forever
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Join Date: Oct 2014
Location: Portland, OR
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Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder

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Did you ensure the chain never went tight as you pedaled several full cycles of chain rotation (say a dozen or so pedal revolutions? If it goes tight because of crankset or cog/FW eccentricity (very common with lower cost equipment - that's one reason track gear costs so much) you are putting very high loads on the chain, possibly far more than you could ever do with your legs. I see to it that I can always wiggle the chain up and down a half inch. With lesser equipment, it sometimes takes me a few minutes to get the hub set so I always have that 1/2" but won't drop the chain when it is at its loosest.

And on chain stretch - there is only one really good way to measure it. With an accurate ruler or tape measure. (Between the 1 foot and 2 feet marks on a steel tape measure is as good as anything.) Measure from the forward edge of a chain rivet to the forward edge of the rivet one foot away (12 pairs of links). On a new chain this is 12" exactly. Worn but rideable - 12 1/16". 12 3/32"? That chain is shot.

Your cogs will wear to match the chain AND you chain will stretch to match the cogs. Put a new chain on old cogs and very quickly the chain will be stretched and be an old chain.

So, is this a new chain over an old cog? If so, the stretch you see is completely expected. Does this chain run smoothly over the cog now? (It might have been a little rough when you put it on.) If it runs smoothly and you have 1/16" or less stretch, all is good. Just ride it until you hit 3/32" of stretch or it feels funky. That could be quite a long time. But the time will come when a new chain will not work at all. At that point, you can keep riding what you have but to upgrade will require a new cog, chain and probably chainring.

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