Will this front mech fit?

[AdrianS]

The front changer on my Trek 7.3 needs changing. I think it was a shimano c101.
The rear changer is a Deore; can I fit a Deore at the front? I looked at one and the internal width for the chain seems narrower than the old one and also the instructions for the Deore says that the chain may foul the changer with certain gear combinations.

 

[JensR]

You probably want a top-swing derailleur (the cable goes down under the frame and up the downtube towards the handlebars).
According to the Trek site, the bike uses a M191 front derailleur, which is from the Tourney range. (You can get them from a few sites - see http://www.google.co.uk/products?q=...esult_group&ct=title&resnum=3&ved=0CCkQrQQwAg).

You would have to check the exact model of Deore changer - make sure it can take the same chain width (8-speed is fairly standard though) and the same size large chainring - the Trek site says 48 teeth is standard. A lot of the Shimano derailleurs mention "48" or "44" - you would want one that mentions 48t.

The chain foul issue will apply to all front changers - a narrow cage will give a quicker shift but may be fouled by the chain more. Basically you should try and avoid the chain rubbing against the cage by changing gears. When you are in the middle chainring, avoid the smallest and largest cassette sprockets. When you are in the biggest chainring, avoid the biggest cassette sprockets (and vice versa for the smallest chainring).

Hope that helps,

Jens