I have done a little research (partly to satisfy my curiosity) and this is what I have found. The Tiagra FD-4503 is designed for a 45mm chainline (per the service instructions at https://si.shimano.com/pFD-4503dfs/s...0A-001-ENG.pdf). The MTB FC-M530 crankset has a 50mm chainline using the recommended 113mm BB (per page 51 of the archived Shimano specifications at file:///C:/Users/eggma/Downloads/2006_SPECIFICATION.pdf). I believe the above 45 and 50mm chainlines are the standard Shimano specs for road and MTB triples, respectively.


Bottom line, your FD may just not be able to extend quite out far enough. Don't believe you can use a shorter BB; what I am seeing is 113 is the shortest V2 Octalink available and if you could find something shorter your frame might not have room for the cranskset to move inward anyway If you like the gearing then try to find a FD that would work with your shifters and crankset. I am real happy using older Shimano MTB FDs (FD-M650/M735/M900) that work great with friction shifting (and Campy brifters that have "microsteps" for the FD) but don't know if they would work with Shimano road brifters. Good luck.