I didn't recall that the Expedition brakes don't fit inside of 15" wheels, but I should have as I think we discussed that before.
I'm personally not at all sold on electric parking brakes. For me they don't solve a problem that I have, and I'd rather be able to do things like partly set the p-brake when I'm doing things like pulling new winch line onto the drum.
The math is pretty simple for figuring out the brake torque, can even then calculate an equivalent "Horse-Power". Coming up with all of the numbers to plug into the equation isn't always so simple. Line pressure is fairly easy, as is caliper piston area. Finding the pad's centroid and it's radial distance from the axis of rotation takes some educated guessing, a fair bit of math, or some CAD software. The real bugger is the coefficient of friction of the brake pad's compound. Most vary with temperature, some quite widely. If you don't know your brake's normal operating temperature (who doesn't, right? snicker) then you're left with either guessing (right about "there"!) or using an average.
I had more, but I figured that I'd best step down off that soap-box......