Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
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Try this, which requires 2 people. Shift the bike into the problem gear combination and put it in a corner of the room with the front wheel against the other wall. Have someone sit on it and load the pedals (try to ride through the wall) while you carefully observe the chain on both sprockets Front and rear. If there's enough wear to cause skipping under load you'll see the chain slide forward or back on the sprocket and climb outward on the teeth.
If it does so significantly, either the chain is stretched, or the sprocket is worn. Start by measuring the chain, if it's OK (less than 1/2% stretch) it's the sprocket, but if the chain is stretched the sprocket may or may not be worn also. You won't know until you replace the chain.
An ounce of diagnosis is worth a pound of cure.
“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin
“One accurate measurement is worth a thousand expert opinions”
- Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance