I have an '03 Sport 4wd (not Sport Trac) that I just put on '16 OEM Explorer rims. I too at first thought that hub rings would resolve my difference in center hub bore sizes. You will find that you need more than hub rings. The problem is that the brake rotor center hub size is not the same diameter as the rim size wheel center bore. The '03 brake hub center is larger than the wheel center bore size on the '11 rim. The wheel hub rings are designed to go from a larger wheel center bore to a smaller diameter on the brake hub center. This is the reverse of what you are trying to do (going from a smaller wheel rim center to a larger brake rotor hub center).
I had to go with a custom made hub centric wheel spacer from MotorSport-Tech.com. They have an online site that will prompt you to select the year of the vehicle you are putting the spacers on and the year and rim size that you want to use. Lenny from MotorSport whom I telephoned explained to me exactly what I needed and mentioned he does this all the time for people like us whom want to have newer rims on older vehicles like the Explorers. It is best to try out the wheel spacers configurations online and then talk on the telephone to "Lenny" who really can do a little better for a discount then the online listed price. I needed a 1.25 inch thick spacer for mines.
If you try and mount the rims with regular non hub centric spacers, you probably get a lot of wheel shaking due to they originally were meant to be mounted and centered by the brake rotor center hub with the rim center bore on the wheel.
