okay, there seems to be some confusion here so i'm going to be as clear as I can be so everyone's on the same page:
1) the whole point of this thread was me asking if someone could explain the wheel clearance diagrams. specifically the difference in caliper width between the Wilwood 140-11899 caliper and the 140-6163 caliper. *BOTH ARE FRONT DISC BIG BRAKE KITS FOR ABS SYSTEMS*
2) no one, not a single person, gave me an explanation of the wheel clearance diagrams (which is fine; still learned some stuff so thank you)
3) i *never* mentioned anything about a rear brake kit. Maybe someone else did in passing, but that's not the focus here.
4) i simply want to know if the posted wheel clearance diagrams definitively state that the 140-6163 caliper (the 4 piston) actually sticks out farther from the wheel mount surface than the 140-11899 caliper (the 6 piston)
Regarding the brake clearance diagrams, the idea is that you need ~3mm clearance to caliper and rotor to the drum and spokes if your wheel. They’ve provided a simplified shape for reference
That one looks to be to scale, so you should be able to print it out, adjust the print scaling until the 2.5” center registration matches a ruler. Ideally, verify the other dimensions.
Then, cut it out, remove your wheel and place it against the hub mating surface and you should be able to tell if the kit will fit or not.
As you’ve noticed, the Dynalite caliper is narrower (and less stiff), it’s just that Wilwood hasn’t bothered to engineer and market a kit with a bracket for it.
As to why they don’t offer a cheaper 4-pot kit, you could speculate that since it was designed before the ST, and there were simple SVT upgrade options for the base Fiesta, they probably decided that the type of clients who would spring for a Wilwood kit were likely more “serious” and the 6-pot caliper would sweeten the deal.
As for working with customers, Wilwood is a small company with a large customer base. They’ll certainly design you a custom kit, but the engineering fee and one-off production is going to cost somewhat more than a package BBK - it’s usually meant for customers with race cars that have a real budget.
They probably haven’t decided it’s worth it to put the design effort in for designing yet another kit when they have one available
already or just haven’t gotten around to it, as there are new applications much much larger potential customer bases that their design team are certainly going to pursue first, because at the end of the day they have to pay their people and budget engineering hours for a project.