My 50-39-30 triple crank has been equipped with a 28-tooth granny ring for several years, and it works well. The crank is Shimano 105, and the original rear derailleur was a 105. I'm now using Tiagra front and rear derailleurs. I can't remember if a changed chain length or not. When I need a new chain, I use the Lennard Zinn method of measuring around big chain ring and big cog and adding one link. Seems to work well.