Originally Posted by
MattFoley
I don't know that I understand about "shifting twice or even three times [sounds like bologna for an 8 spd cassette] in the opposite direction" as you mention, except to note that Shimano STIs (and I think Campy and SRAM too) allow you do downshift multiple cogs in a single motion (for Shimano, it's up to 3 cogs).
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.