As I mentioned, the back of the wheel cover is the same circle but with the center coved out. The fits over the wheel pole. From the bottom flap, it is 4-1/2 inches wide, then to 5-1/2 inches wide, to 6-1/2 inches wide and just above the cove, it is about 9 inches wide to the center fold. When I stack the front and backs, if I have the front or back a bit larger, I trim to make the cuts match.
Here you see two stacks so that once the
pattern is cut out, both the cover and backing are cut out.
Below is the batting put on the back side of the back wheel cover. I sew from side to side to attach the batting to the fabric.