I have a 48 tooth main ring with 165 cranks. FD is Sora double and rear is Tiagra short with Shimano 7 freewheel. If I can put this 34 ring on it gives me sufficient range for the next few months and time to evaluate before any larger purchase of cranks. (likely I would go to 170 0r 172.5) I'm using Diacompe bar end friction shift.

Is it necessary or desirable to replace large ring as well?

  • If the BCD is the same and the width is OK then it should work. The small ring doesn't care about friction vs indexed. The only real issue is whether the "jump" is too great for reasonably smooth shifting, but there are plenty of 48/36 combos around, so it should be pretty safe. – Daniel R Hicks Jul 5 '15 at 20:23

34/50 is a standard combination, so 34/48 should work without problems. Friction shifters just make it easier to overshift and trim on the fly.

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