[QUOTE=BloomBikeShop]Actually this derailleur sucked even when I had the stock triple on there (ie when it was new!) I could adjust it properly but that adjustment lasted maybe 3 days, so I'm happy to buy a new one
[quote]
The Tiagra derailer is just as good quality as the Ultegra, except for being a wee bit heavier because some of the Ultegra's parts are aluminum, instead of steel.
If it doesn't stay in adjustment, that's 'cause something is too loose, has NOTHING to do with the quality of the derailer. If you had mentioned in what way it went out of adjustment, I might be able to guess what is loose.
See:
http://sheldonbrown.com/derailer-adjustment
Originally Posted by BloomBikeShop
Wouldn't a double front derailleur work better for a double crankset?
I don't see any reason to think so.
Originally Posted by BloomBikeShop
But my main concern was getting the right size for my seat tube...
My post is a 27.2 but my seattube gets a tad bigger as it goes towards the BB, so I'm not sure whether it would be 28.6 or 31.8.
Anyone know for sure, or know which bikes generally have which size seat tube?
Steel frames are generally 26.8. Aluminum frames commonly have fatter tubes.
If you remove your present front derailer, and look inside of the clamp part that holds it onto the seat tube, you will see the size stamped into the metal.
I still think you're wasting your money to replace this.
Sheldon "If It Ain't Broke..." Brown