Hi! I did have a Ford Fiesta MK6 LX, think of the ST it is the same as your LX just has a body kit, alloys and is lowered. My point is the wheel arches are the same on the ST as yours and it has 17inch alloys and is lowered (not sure by how much) but none the less it is lowered and it does not rub. You probably know already but u will have to have low profiles and pos a spacer. may I recommend putting new shocks in as well and not just lowering it on springs alone as I presume u still have the standard shocks on the car (the shocks will not support the shorter springs)
awrite al try that..