I thought I might post three photos of the wheels on my three trailers, with some comments about them.
My first photo shows my 71 Caravel
with original axel. You can see that if you judge it's condition by the space between the top of the wheel and the wheel opening, you would say it is good. After 41 years, I have my doubts, yet there it is with maybe 1.5 inches between the wheel well cutout and the top of the rim.
The second photo shows my 75 Argosy 22' with dual axels. Wow! Look at the space between the top of the wheel and the wheel well cut out. Must be 5 inches. Well, they are original axels and when you look at them from the rear, the arm is up, not even horizontal. They are in need of replacement, but by the wheel well test, they are great.
The third photo is of my 74 Argosy 20' with a new Dexter axle and 16" wheels and tires. The wheel cutout vs. the top of the wheel is the smallest dimension of the three I own, yet it is the newest and best axle.
So, watch out with the quick and dirty test to see if the axle is good or bad, judging by the top of wheel to wheel cutout. It may not agree with reality. Note especially how high the wheel cutout vs. the banana wrap to side transition is on the 75 Argosy. I don't know how common that high cutout is, but it is original on mine.