I have a Specialized Allez sport triple with 105. It has never shifted well up front. It came with Tiagra FD and Specialized crank. The 105 didn't help. I found a Ultega double with 109.5 BB for a great $. Will this work on my bike?

Hello. it will 'fit' on your bike wether it works you will have to see. as your Tiagra shifter is designed to have 3 positions for the front derailuer and the double crank will only use two is likely that it will not shift any better.

If you're having shifting problems it's probably due to the way the derailleur and shifter are adjusted. Changing to a double may improve shifting but you'll be giving up a lot of gearing options needed for climbing hills.
BTW, Shimano road triple shifters have 4 main positions for the 3 chainrings.

Al

You'll probably need to convert the left STI lever and the front derailleur to a double as well. You can buy the left STI lever separately (try jensonusa dot com, there are probably other sources as well). Or you can just go back to the triple and work harder on adjusting it. Triples are hard to adjust correctly. I know, I just converted one of my bikes to a double for that reason.

Just readjust the front der. You can use triple STI's on a double, but your problem is likley just adjustment.

In the Tiagra group and 105 group the shifters are double-triple compatible. In 9-speed the Ultegra shifters are double triple compatible, in fact they are the same shifters.

The set-up and adjustments for a triple front derailleur and shifter is exactly the same as for a double. But accuracy seems to be more critical. The rough shifting often associated with a triple is due to the differences in chainring sizes, the size of the smallest chainring, and the more severe chain angles.

Al1943, thanks for setting me straight.

Depending on which type of double you're talking about (standard or compact), the triple should shift at least as well as the double. A triple has roughly the same gear range and drop on the two bigger rings as a standard double, and should shift between those rings as well as the standard double.

The compact double has a drop (tooth count difference) between its two rings that is roughly the same as the drop between the middle and granny rings of a triple. Because of the large drop, shifting between these rings will always suck in relation to a smaller drop. With a triple you will sometimes have to shift down onto the granny. With a compact every front shift is like that.

So in terms of shifting, a triple will sometimes shift worse than a standard double (when it goes to the gear that the standard double doesn't have). Yet most of the time the triple shifts better than the compact double.


Now all that said, the reason your shifting sucks is a matter of adjustment. In my experience, triples are harder to set up well than doubles. But when you get it right, it will shift like butter.

(usually)