What's happening here? Front mech / chainring position issue

[renaldo]

Going to fit the front mech on a new build and I've run into an issue getting it positioned properly that I've never encountered before. With the mech as low as it will go to avoid the trailing part of the cage from hitting the chainstay its still nowhere near the chainrings. Below is a comparison of my bike with a catalogue shot.
I think everything is the same in terms of frame, cranks and front mech with the exception that I'm running a 42T TA Specialities outer ring rather than a 44T Raceface chainring in the catalogue but can't believe that would that make much of a difference.
I believe the mechs are the same, top swing bottom pull M570 LX. I did wonder if the clamp is the right size as I don't know if its original to the bike. It looks a bit too big but its a 31.8mm clamp and I've measured the seat tube outer diameter as ~32.6mm. Its an aluminium frame and takes a 27.2mm seatpost, so I guess 31.8 should be right? Would a different clamp size make a difference to the positioning problem anyway?

Below is an image from the catalogue and then my bike.

 

[ishaw]

Re:

The issue is probably related to the mech type, I'll probably get this the wrong way round but I think your mech is bottom swing rather than a conventional top swing with the clamp band higher up the seat tube. Not quite the same, but I can't use a mech with a low clamp on my RTS team as the same issue occurs.

 

[hamster]

Firstly the chainrings are irrelevant - a 42T ring is the same diameter regardless!

Shimano made so many different variants to their front mechs that it's almost impossible to follow. However they did ones for diferent seat tube angles to avoid the problem you have. Try a couple of others is the long and short of it.

 

[renaldo]

Re:

Thanks for the replies. I guess I'll have to do some experimenting with different mechs until I find one that works!