Overall you have indeed done a pretty good job - you've shown a great deal of patience and care with the construction of each wheel - extending beyond the cylindrical construction to the spokes/rims - and while there are some issues I'll address, I'm quite pleased with your work.

There are two main issues - one is a little hiccup in construction, and the other is a very common mistake for which this challenge kind of serves as a trap.

Starting with the hiccup, if you look at wheel 24, the problem is that the face of the wheel was drawn with a very wide degree - basically circular. That on its own is fine, but it tells us that we're looking straight on at the wheel, or close to it. This means that most of its depth is going to be "unseen" - that is, since we're drawing on a flat page, we can only see distances that exist parallel to the picture plane. Any depth is conveyed through foreshortening. When looking at the face of a cylindrical form like this, you're going to see very little of the other side, and there's not going to be much of an offset between the front face and the far face of the cylinder. So in this case, the front face would almost entirely overlap the back face - whereas you've drawn it to be offset quite a bit to the side, creating a rather strange visual inconsistency.

So, to put it simply - if we're looking down the face of a cylinder, remember what that means about how it's oriented in space, and make sure you don't have the other end sticking out too much from the side. In all your other wheels, it's fine, because they're much narrower and therefore we understand we're looking at them from an angle, with some of the wheel's thickness being expressed visibly on the page, and some of it being "unseen".

The other issue - the trap - is actually one you definitely tried to address, but had some issues in doing so. That's frankly better than most students. It comes down to capturing the tire treads as texture, in the manner explored back in Lesson 2. This is less of an issue with tire treads that have relatively shallow grooves, like those from the demo, as well as wheels like 16 and 20. There are however a lot of tires in your set that have much chunkier tire treads, and I commend you for trying to play with them quite so much.

You're definitely moving in the right direction here, working with solid black shapes, and I can see through your notes that you are trying to establish cast shadow shapes. The only problem is that more often than not, you're missing a component that causes them to read more like you're trying to fill in the side plane of those tread "chunks".

If you look at this example, you'll see two cases. The correct one, on the right, has a completely empty silhouette - you can actually see how the silhouette's corners defines not only the top plane, but also the side planes as well, and the cast shadow exists outside of this space. In some of your tire treads, you definitely just end up constructing your treads and then filling a side plane in with black (like in wheel 19, where it functions similarly to the left side of my example image). In cases like 24 however, you're definitely trying to work with cast shadow, but the problem is that the silhouette of each chunk doesn't have those clearly defined corners to imply the presence of side planes to make the chunk feel three dimensional. As a result, our brains interpret those cast shadow shapes as defining the side planes instead, and the illusion kind of breaks down.

All things considered I'm still very glad to see that you're pushing in the right direction - you just need to think more about the specific silhouette of each textural form. It's not an easy thing, but the more you pay attention to that, the easier this all becomes.

Despite that, you're doing well. I'll go ahead and mark this challenge as complete.