deep_sky

I have currently a 5503 front derailleur, and neither myself nor any of the bike shops I frequent have been quite able to remove the rub in the lowest gear. I am wondering if going to a more modern derailleur might help, and if so, which model? For reference the small ring has been switched out with a 26, and the rear cassette is an 11-30. The chain isn't bottoming out in the derailleur, but it just can't go any further inward without interfering with the shifting into the large ring. The mechanic at my favorite shop says it's because of the shape of the 5503 derailleur being incompatible with the newer Tiagra crank.

Andrew R Stewart 

Shimano makes their stuff work pretty well within a narrow spec range. The swap out to a 26t granny ring exceeds theis range. Where the chain now passes through the Ft der cage is lower towards the cage end then intended. The heavely sculpted cages will ahve bulges to help shifting and reliefs to insure chain clearances. When different ring or cog diameters are used these cage shapes don't line up with the cahin as intended. Add to this that Shimano considers a small amount of chain rub acceptible no wonder your post. Andy.