Originally Posted by
aesmith
Hi,
Quick question. The 105 STI is the same for either double or triple cranksets. So three main positions for outer, middle and inner ring.
Sorry but that's not correct. Shimano road shifters for triples have four (4) main positions. The small ring position is with all of the cable out of the shifter. The second and third positions are used when on the middle chainring, the third position can also be used to trim the big ring. The fourth position is for the big ring. Most Shimano road triple shifters also have an additional trim position for the smallest ring.
For a double I would release all of the cable from the shifter, remove all slack and attach the cable to the derailleur, same as with a triple.
But if you really want to try using the third and fourth positions for the double I think it can be done. Make sure the cable end is seated in the shifter. Reel in the cable as far as the shifter will take it. Release the cable one stop with the smaller shifter, this will put it in the third position. Then attach the cable to the derailleur with no slack. Adjust the tension as needed with the barrel adjuster. I've never tried this so I can't really recommend it.
Al