Now, I'm not qualified to offer much advice, except to say that I'd be very much surprised if 4500 Tiagra had a different pull ratio than 6500 Ultegra. I have 9-speed ST-R600 shifters (these replaced ST-6503 on my bike) combined with a 9-speed 105 triple (FD-5603) front changer and the combination works as though intended that way. I guess, my uneducated hunch, I'd have to say, "It should work."