I've got an older Campy Chorus crankset, 135 mm BCD, with a 52-tooth outer chainring and a 42-tooth inner ring. The outer ring is stamped "-52/42-", has pins, and some of the teeth are what I'll call "scalloped" on the inboard side. The inner ring is stamped "-42-" and all the teeth are symmetrical. I'd like to source an inner position 39 tooth ring for an upcoming build. Is there anything special I should be looking for or concerned about? It is hard for me to visualize how matching the chainrings on this crankset has a significant impact on shifting, but......

This issue may have been covered before on BF, but I could not find it. If indeed it is out there, I'll appreciate a link to the thread.

Thanks for any and all input!

Dean

It will shift better with matched chainrings. Most common were 53/39. Your 52/42 big ring will work, but won't shift as smoothly.

There's lots to be concerned about, but a 135BCD 39T chainring isn't one of them.