Campy Chorus Compact question

[DebW]

Thanks for the ideas. The bike came fully set up by the bike builder, so I am 99.9% sure everything is positioned correctly. As for the front derailleur, I was supposed to get the whole gruppo, so I assume it's a compact derailleur, but I will check.

Look at the pictures on the Campy web site. The difference is in the inside plate of the FD cage. For a double, there's not much difference in the inner and outer plate, the inner is just a little deeper. For the compact, the leading 1/3 of the inner plate is much deeper. For a triple, the whole plate is much deeper. It's the inner cage shape the helps lift the chain smoothly to the next larger cog. The bigger the difference in cogs, the more difficult it is to make that happen smoothly.

BTW, trimming is when you 'click' the gear shifter and the chain does not move out of its position, but it is tweaked (I don't fully understand the mechanics of it) such that it quits making the noise that it was making. I'm sure DebW could give you a better definition.

The noise is the chain scraping on the FD cage. Trimming shifts the cage until the chain is centered within it and not scraping it. When you shift the rear derailleur, the chain angle changes and the front derailleur cage needs to move to remain centered over the chain. There is some leeway as the cage is wider than the chain, but it can't be wide enough the accommodate the full chain motion (i.e. the chain's position on its most inside and most outside rear cog) or you'd get lousy shifts. Ideal shifting of a double front derailleur is to always throw it to it's limit, wait for the chain to shift to the new cog, and then trim or center the cage over the new chain position. Easier done with friction shifters than indexed. Indexed shifters are a compromise and entirely unnecessary (IMO) on a double.