I wonder what kind of situation could lead to the need for brake ducts? (I presume they're for cooling purposes?) The wheels themselves should generate enough wind vortex to cool the brake calipers IMHO. Have you tried to see if you can get the brake disc to glow on an ST?
Competition/hard driving. Having a rally modified ST myself, i have cracked 2 discs so far due too exessive heat. One disc being a cheapish brand, Tarox. The other being a proper 2 piece AP Racing disc. So yes, cooling is needed for hard running.
If you use high performance brake components, ie pads, they will generate more stopping power, and therefore more heat, so yes we need improved cooling
![Fiesta ST Build [Pt.19] "M-Sport Rally Brake Duct Install"](/img/logo.svg){kind=logo}
