Originally Posted by
WheelsNT
But what kind of front derailer? Many folks in the tandem world have noticed that the 105 FD is actually stiffer than the Ultegra and shifts better than the Ultegra with the load of a tandem. As others have mentioned, if it's shifts to the big ring that are the problem, stiffer chainrings such as Dura-Ace will help.
I would disagree with this. The difference between the 105 and Ultegra triple FDs is that the 105 is designed for an 11-tooth difference between large and small rings, and so works best with those combinations (e.g., 50-39-xx, 53-42-xx, etc.), whereas the Ultegra is designed for a 13-tooth difference (e.g., 52-39-xx, 55-42-xx, etc.). If you run a difference between middle and big rings that the FD is not designed for then the derailleur will be at the wrong height and you'll either risk shifting the chain off of the outside ring, or you it won't shift from the middle to the small well because the shifting tab on the derailleur won't be lined up with the chain. Size of the inner ring is far less important for the choice between FD models, except that the closer in size the inner is to the middle, then the smoother the shifts will be.
As for stiffness differences between the 105 and Ultegra models, I haven't noticed any, but maybe the Ultegra is slightly less stiff because it has a longer/deeper cage to allow for the bigger difference in rings sizes. However, this factor is far less important then choosing the FD that matches your middle to large ring tooth difference. Also, there are differences in cage widths between the old 9-speed models (5503 and 6503) and the newer 10-speed models (5603, 5703, 6603, 6703) and again you need to have the one that matches your chain to have optimal performance.