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
Mentioned: 22 Post(s)
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First of all is a rear suspension bike, or hardtail? I ask because I'm looking for something that would act differently on and off road.
If you watch the action of a chain feeding onto a chainring, you see that the points of the teeth must slip between the plates of the inner chain link. if the chain is feeding from an angle it's possible for the point to hit a plate and lift it rather than slipping in. If that happens the chain will derail.
The middle ring of a triple has shift gates to aid shifting. These also act as convenient places for the chain to derail if coming from an angle.
Take some time to pin down exactly when the problem occurs, for example only on the innermost rear sprocket, or with various ones? Are bumps a factor? Does it tend to happen at a certain point in the crank rotation? etc. As you pin down the variables, it might point you toward the source of the problem.
I asked about suspension, because sudden swing-arm movement can momentarily slacken the upper chain loop making it easier to drop on a hard bump.
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