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Old 04-30-18, 09:06 PM
Andrew R Stewart 
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The lower edge of the inner cage plate needs to clear the tops of the middle ring. So a der with too "deep/tall" an inner cage plate shape could rub an a 42T ring but clear a 39t ring. Also the cage's contours might not match where the chain is running past them if the ring was the wrong size, affecting the chain's lift during shifting. Andy
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