Which front mech do I need?

[onlyhuman]

My daring quest to obtain lighter gearing continues. I have now replaced my 53 x 42 front chainwheels with 48 x 39. The gears are working but there is a lot of trimming required, I think because the brazed fitting front derailleur is too far above the large chainwheel and won't adjust down further. It's early 90s 8 speed Athena equipment. I'm thinking I will have to get a secondhand derailleur (off EBay?), but how do I know what model will suit the chainwheel?

If anybody here has the bit I need I would of course be interested in buying it.

 

[PpPete]

Deore M530/M531 will take a 48 tooth chainring, which one of those you need will depend on chainstay angle. I don't think you need to worry about the 12T min difference as your front shifter won't be indexed. Someone with more knowledge will hopefully be along soon to confirm that. Of course polluting a Campag equipped bike by adding Sh....no components may not be acceptable?

 

[onlyhuman]

I don't think you need to worry about the 12T min difference as your front shifter won't be indexed. Someone with more knowledge will hopefully be along soon to confirm that. Of course polluting a Campag equipped bike by adding Sh....no components may not be acceptable?

Thanks Pete. I'd like not to pollute the bike!

I have Ergo shifters, and they click when I use them, are they not indexed?

 

[PpPete]

Not sure about Ergo....
I thought all Campag was non-indexed front - but all my stuff is Shimano (or cheapo Shimano compatible) so I don't really know.

 

[onlyhuman]

Not sure about Ergo....
I thought all Campag was non-indexed front - but all my stuff is Shimano (or cheapo Shimano compatible) so I don't really know.

It's indexed in a way, in that it moves in jumps. This helps with trimming.

 

[MartinC]

I think you're right. You probably won't be able to shift the mech down far enough because of the brazed on mech hanger. Usually they'll just about let you fit a 50 ring. In the 80's people were more interested in fitting 55 tooth rings for TT's so frames were made accordingly.

If you change the mech you may still have the problem - depends on the dimensions of the mech so you'll only be able to tell by trial and error. A mech with a cage profile better suited to a 48 tooth ring may work better even if you still can't adjust it properly.

Your LH lever isn't indexed. It's got a ratchet that allows you to select many position so it will work with just about anyt front mech.