Well, I don't really expect you to understand unless you've tried coding a 3D graphics engine. You'll just have to take my word for it.
So far you're not really trying.
Try to really understand the diagrams in my first post. if you don't listen, you won't learn. What you are calling a steel "rim" is actually a whole wheel, and the rim itself looks nothing like a real steel rim. A steel rim follows the yellow lines in the rim editor, which you are failing to observe.
You really need to try and learn to use the rim editor and then you will find there are plenty of triangles left for your spokes.
Also, go for a walk and have a look at some real steel wheels.

What i meant by "old steel rim" is its design and shape, if you know. According to shape of the rims of old cars, they are mostly made out of one piece and there are holes on it. Modern rims like alloys have "spokes" or "arms" or whatever, you name it.

