Old 12-31-20, 11:51 AM
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Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970

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There is no measurement or answer to your question.

All rear derailleurs have two basic specs; max cog and capacity.

Max cog is the rating based on design that design to use a 28t, 34t, 40t, 50t, etc. cog. It technically has nothing to do with cage length, but every mfg designs them together because an 11-50 cassette has capacity issues even with a 1x.

Capacity is the amount of extra chain can be stored, so to speak, between the derailleur pulleys (cage length). The the longer the cage the more capacity.

Wolftooth, and others, have an adapter that lowers the derailleur away from the cassette and allows a larger max cog.

But as you noted lowering the derailleur on 16”/20” wheels will probably be a deal breaker. I’m running a Wolftooth RoadLink on my 26er with a 40t and my longe cage derailleur sits 5” off the ground. I’m one bad line away from walking.

If you have a specific derailleur that will run a 50t, you can probably get an answer to cage length question. But overall maximum derailleur vertical “stretched” length might be more important.


Last edited by 70sSanO; 12-31-20 at 11:55 AM.
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