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: 20 Post(s)
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1- chain is too long and on the small/small combination the RD cannot take up all the slack. This is obvious because the lower loop will sag visibly, or you can check by rotating the cage and see if there's room to increase tension. If there is, all is fine. (BTW RD springs don't get weaker over time less than eons). On some RDs you can adjust spring tension, but this lowers the efficiency of the system.
2- a sticky freehub is spooling the chain forward slackening the top loop. Probably not the case, because it causes slack problems far beyond chain slap, and you'd know.
3- chain is close to chainstay coming off smallest cassette sprockets. Consider the radius of the 11 or 12t sprocket and you'll see that the chain comes off pretty low compared to the height of the stay. With so little clearance it doesn't take much of a bump to raise the stay and slap the chain, so we shouldn't call it chain slap, but stay slap. There's no fix if you coast over bumpy roads in high gears, so that's why they make chainstay protectors. Either buy one, or improvise your own, and accept it as a normal characteristic.
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