Originally Posted by
HillRider
Yes, the 2/3 means the front shifter will work with either a double or triple crank. The shifter will have four clicks that give four front derailleur positions, one is a trim. For a triple crank you use them all. For use with a double you adjust the front derailleur's low limit screw to keep it from moving too far inward and set the shift cable tension to use the outer three fd positions. (small ring, trim, big ring)
The reason for setting the double that way is that if you use the non-functional click, the cable merely goes slack. If you set the shifter to use the inner three positions and try to shift into the fourth non-available position you can break something
I have 105 5600 shifters that are 2/3 speed. They are set up per the instructions to use the lower positions: click all the way to the slack position and set up the front derailleur on the inner ring, shift up to the large ring (middle position) and use the high limit screw to prevent shifting to the highest position. I am not directly familiar with MTB or flat bar shifters, but the principal would seem to me to be the same. If you set up on the high two positions, you can still shift the shifter to the lowest position, as it does not know or care what the derailleur is doing, then you would have to shift twice to get to the large ring. Maybe on mountain bikes you are more worried about breaking something, but on my bike you would really have to push hard to get past the limit screw.