Originally Posted by
mcours2006
I didn't know that either. How new/old is this feature, and on what models? I've got an older model Tiagra triple but I've set it up for a double crankset, and it does something like what the OP describes, only not quite as pronounced and on the middle ring.
It's been around for all ~12 years I've been into road cycling. The Sora 8 speed triple shifters on my first road bike had a trim feature for the little ring IIRC but that was it. My Ultegra 9 speed triple shifters can trim the small and middle rings. My Ultegra 10 speed triple shifters can trim all three rings, as can the latest Claris and Sora groups (nice of Shimano to add these 'high end' features all the way down the line). I presume that my new but yet to be installed 105 11 speed double shifters will trim both rings.
Shimano used to have a chart online showing the trim function capabilities of various shifters but I don't know if it still exists or if it has been updated.