Quick question. The 105 STI is the same for either double or triple cranksets. So three main positions for outer, middle and inner ring.
The instructions suggest that on a double you should be using the two inner positions. However they caution that pushing the levers too far (towards the non-existent outer ring) could break the STI.
Any reason not to use the two outer positions instead, with the innermost left unused? Instead of danger or breaking the expensive lever, all that would happen is the cable falls slack if the lever's moved too far.
Ta in advance, Tony S