Trying to get my bike which is set up with Shimano Sora triple working with a double crankset that I put on. I've so far done a lot to try and keep it shifting right but I haven't had much luck. What do I need to change to fix this: The derailleur? The brifter? Both?
how is it currently shifting? will it not reach one of the rings, or does it do so inconsistently? or is it dropping the chain off in a particular direction? two options, one dirty and the other standard. the dirty: set the limit screws of the derailleur so that the brifter can't index to the non-existent third ring. the standard: check your spindle length- you might be able to change the range the brifter has to cover and thereby improve the shifting.
The triple shifter shouldn't be a problem. I use Shimano 105 shifters which can handle a triple, they don't even make a double version.
I set mine so it uses the tightest two positions. That way I can't overstrain it.
Your limit screw may be set wrong if the chain throws off. The Park Tool site goes through the whole process of setting it up. Note that the indexing is the last adjustment after you've got the mech properly aligned and the limit screws all set up.