A.
anwered by: canteau
Using the Shimano 105 FD-5700 10-Speed Braze-On Double Front Derailleur with a 9-speed drivetrain will work, although not as well as a 9-speed front derailleur because the cage on the Shimano 105 FD-5700 10-Speed Braze-On Double Front Derailleur is slightly narrower than a 9-speed front derailleur. You should still be able to shift up and down, there just might be more chain rub in certain gears.