My LBS wants to replace the Tiagra front derailleur on my son's bicycle with a 105 front derailleur. At first I thought fine, it will shift better (maybe). Now I am wondering. The Tiagra is a 9 speed derailleur; the 105 is (I think) a 10 speed. Maybe this doesn't make any difference since it's a front derailleur only. It's a triple chain ring. Will this be a problem at all?