I am currently running a 52/42/30. I want to swap out the 42 for a 39. Does the 39 have to be pinned and ramped like the 42 is now? TIA
If you're not using front indexing, there's no problem as you can overshift to make the chain move. It may be OK even if you are - on my MTB I have fully-indexed STX levers and an ancient Deore DX crankset with the original rings. It works.
Front indexing is still a pretty stupid idea though ;-)