Originally Posted by booyah
I don't understand why he'd need to replace either of the shifters. Certainly no need for the rear, and I thought the new Shimano front shifters were all double and triple compatible.
You might first want to try riding a double with a 12-27 cassette....
The standard Dura Ace front shifters are double
only and the rear dérailleur may not work satisfactorily with the 12/27 cassette, there usually isn't enough adjustment with the B screw to keep the top jockey wheel from hitting the largest cog, and it may not have enough wrap capacity. Usually a long cage rear dérailleur is necessary. The rear shifter won't have to be changed if a long cage or MTB rear dérailleur is used.