We want to make the rim more versatile so we are actually going to detach the hubcap from the rest of the rim and model the stuff that's beneath it. This way, you can also have a spare tire since the spare tire doesn't have a hubcap on it.Select the polys shown in red and detach them. Name the detached polys "Hubcap" and hide them.
Select the edges shown in green and extrude them inwards as shown.
Select the edges shown in green and make another extrusion as shown. Delete the polys shown in yellow and delete them. Select the vertices shown in light blue and cale them inwards a little.