So my friend is going to upgrade his bike and he's giving his sti for free (Shimano Sora R3030 3x9 sti). My question is if I can use it on my 2x crankset. Will my chaib fall off if I accidentally shift it to the lowest cogs? Is there like a switch on the sti that it can transform to 2x?
This question has been asked before. Yes --- you can. However, you won't have the trim positions that allow you to ride at certain cross-chain gears like you do on the double lever.
You may also find that it only works with the older style short actuator front derailleurs. Perhaps you can post a photo of your front derailleur set up for us.
There is no switch.