So I have been drifting pretty hard in FH3 since release. I have worked a drift tune that I am really happy with, its gets great drifts going and is very easy to control.
So if your new to drifting or looking to fine tune the tune you already have, follow my drift tuning guide in this video:
fully lock the diff, also on deceleration so you can better control entries
balance shocks and springs with a calculator like this one and adjust to taste from there (set it stiff for drifting (like 90-105%), less stiffness for grip (75-100%) and really soft for offroad (20-60%)) Forza tuning calculator - Google Sheets
brake balance is reverse so if your car has 53% front weight you start out with a brake balance of 47% and adjust from there.
tires, springs and roll bars are for static balance
dampers are for transition (weight transfer) balance