You haven't said what shifters you are using. On Shimano road shifters, you have to peel back the rubber hood to find the number. On MTB shifters, I don't know where the number is. Barends, its on the right rubber shift lever. If we knew that I, or others, might be able to tell you what FD would work with a MTB triple crankset and your shifters. Really need both bits of info.


Something that just occurred to me is that the shape of the Tiagra FD-4503 is designed for road rings (its matching crankset the FC-4503 has 30-39-50T rings). Not a huge difference from the rings you are using but the "tail" of the derailleur is further away from the large chainring than intended, and would more likely lead to chain rub.