road double to triple crankset - things to consider
 

Hi,

I picked up a vintage chromoly frame. The previous owner rested the wheel-less frame on the floor, so the existing 52/40 crankset was bent out of shape. I have an existing 48/38/28 crankset I want to use on the bike, but what else would I need to change?

I've determined the existing Shimano double front derailleur won't work - it actually can shift to all three gears, but there is chain rubbing when I'm on the smallest front and rear gears because the chain is so low. I can't move the derailleur any lower or it won't clear all three gears when shifting. So I'm guessing I'll need a triple front derailleur.

But, I'm using the existing Shimano friction stem shifters. Will that have enough "pull" for a triple derailleur?

Are there other things to consider?

You will probably need a new bottom bracket to match the triple crank.

Your shifters should allow shifting to all three chainrings with either a double or triple front derailleur.

Your current front derailleur should work ok with the new crank. The problem you report with the chain hitting the tail off the derailleur is common in small-small but there is absolutely no reason to ever use those gears so the "problem" is easily solved by avoiding it.

+1. Small-small derailleur rub sometimes happens with triple-specific derailleurs. Not a real issue.

Thanks for the responses. Very Interesting. So derailleur rub won't necessarily be solved with a triple derailleur. It's ones of those "you have to live with it" things. Hmm...

I hadn't considered changing the bottom bracket. The "chainline" measurement (center of tube to middle chain ring) is about 50mm, but I can still shift to the largest gear. Is a smaller chainline measurement meant to improve efficiency and reduce wear by having a relatively straight chain?

Typically, the spindle for a triple crankset is longer than a double. Putting a triple crank on a double spindle results in the small chainring pushed into the chainstay if all else is equal. If it works now, don't argue with it.

I went through this recently with an '85 Cannondale SR300.

Initially I was using the original 6 sp. double derailer with a used Campy 9 sp. triple and 7 speed freewheel, with a long-cage rear derailer. It worked as long as I slightly over-shifted up off the granny then quickly brought it back slightly to the middle.

It only took accidentally shifting to the granny, then not being able to get off it on a medium hill once, to make me buy a triple derailer. I got an inexpensive Shimano Sora and have had no trouble with it.