The basic point here is that if you're using Shimano STI brifters with a triple crankset, you need to use Shimano road-triple front derailler. Shimano off-road grouppo front deraillers have a different amount of cable pull, and SRAM front deraillers are sometimes compatible with Shimano (in certain off-road grouppos) and either way don't have the same amount of cable pull as Shimano road front deraillers.
__________________
"c" is not a unit that measures tire width