OK a bit of a basic question, but I might as well ask to make sure.

These are the smaller ones, i.e. front, which I think are 7 x 14.

First photo inside edges of the bead seat.
Second from the outside edge of the rim.
Third from the inside edge of the rim.








Larger, rear wheels, which I think are 8.5 x 15.

Same measurement points as previously








Am I right, am I wrong, am I measuring completely incorrectly?

You are right on width measure the diameter is the bead set to bead seat inside the rim lip the tape outside will give the approximate to work it out. But wheels come in 1" diameter steps on buggies there are a few oddball cars that have used a metric diameter that are one offs.