Originally Posted by
merlinextraligh
If you look at the tool I linked and take the 50/21 example, and you want to get to the little ring to access the lower gear ranges, but maintain your cadence for the moment as Caloso suggests, you need to 34/14, which depending on your cassette would typically involve moving 3 cogs in the back.
Which is why 10-speed Campy is awesome. I can hit both thumb buttons and instantly dump the chain ring and 3 cogs.