Originally Posted by
jethin
To me it seems the key feature I'd like to use them for would be to possibly extend my rd capacity a few cogs via adjusting the effective chain length.
AFAIK this is done by moving the axle back as far as possible to increase chain tension. This increased tension pulls the rd forward a bit, moving the upper pulley away from the nearest cog. Do I have this correct? Any potential gotchas when doing this adjustment?
Yes, that's an old-school trick to get your Nuovo Record derailleur to work with a 30T cog instead of the maximum rated 28T cog Campy specs. But as you suspect, it does come with a cost. The pulley is further from the cogs, allowing a larger cog to be used, but shifting performance can suffer as a result. This is more of an issue with indexed shifting, which is more sensitive to pulley position than friction shifting where you can overshift briefly to compensate for this.