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I have a bike with a 4503 Shimano setup (Tiagra triple, 9 speed). The front derailleur is broken.
I can quickly get a 105 derailleur (5703) at the local bike shop. I just want to be sure that it is compatible with my shifters, and be sure I can get a clean shifting experience.
Differences between the old and new front derailleur:
Can anyone confirm the FD-5703 will work on my bike?
Not according to the Shimano compatibility documents.
Tiagra 4500 series appeared about 2006 and 105 5700 series appeared about 2010 so we need to look at the 2010-2011 archived compatibility document from here and search for 'FD-4503'. The charts say it is only compatible with Tiagra 4503 and Sora 3400 9 speed triple shifters.
To confirm we can search for 'FD-5700', we see it is only compatible with Ultegra 6703 and 105 5703 or 5603 10 speed triple shifters.
However, Shimano is notoriously conservative in its component specifications and compatibility recommendations, so someone may tell you that a 5700 triple front derailleur will work with a 4500 triple shifter - if the two derailleurs use the same actuation ratio they will be basically compatible.
I can confirm that the FD-5703 front derailleur works perfectly with the 4503 group set.
I gave it a try anyway. It shifts seemlessly.
