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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Rear derailleurs don't care about the crank set either way, so no automatic issues.
But there is the question of chain take up capacity, regardless if whether it's a double or triple. The RDs cage length determines the capacity which is listed in terms of the number of teeth. You need capacity equal or greater, than the sum of the differences between the largest and smallest sprocket front and back, ie. 12-26 & 28-38-48 = 14+20 = 34t capacity needed. The capacity requirement is the same regardless of whether you have a triple or double with the same inner and outer chainrings.
There is a bit of wiggle room on borderline cases so if you need 29t and the RD you want has only 27t you might get by with careful chain measurement, and possibly not using the small/small combinations (which most don't use anyway).
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