Your work here is looking solid! It's normal for students to submit relatively small wheels, as the more affordable 'master ellipse templates' come with obvious size limitations, so that's entirely normal. I did notice however that you chose to draw one wheel per page, which was admittedly a strange choice. While there are no rules against it, it does give the immediate concern of a lack of confidence - that perhaps you went with separate pages for each wheel so you could easily toss aside any failed attempts. Our failures are more important than our successes, and where we make mistakes is where we give ourselves room to grow, so in case you didn't include some that may not have gone as well, keep that in mind. The challenge doesn't ask for 25 good wheels, after all.

To that point, I don't actually have a whole lot of critique to offer on the wheels you've submitted here, as they're all quite well done. The only thing that comes to mind is that there may be situations (like on this wheel), where you feel inclined to fill certain areas of your drawings with black. Try and reserve the filled black areas for cast shadows only. It's not uncommon for students to try and use filled areas to distinguish a face of a form from another (like the side face of a box from another), but this can actually be a less effective use of filled shapes. Doing so will make the shadow shapes themselves more difficult to distinguish, and will give up some of the advantage that comes with shadows. Shadows, after all, being cast from one form onto the surface of another, helps us provide additional information on the relationship between those two forms.

This actually relates to an issue I often have the opportunity to point out within this challenge, specifically where students tackle chunkier tire treads - ones that have big box forms coming off their surfaces, leading to them filling in the side faces of said chunks with solid black. While you haven't tackled any such tire treads, it's still worthwhile to convey the same information.

Take a look at this diagram. Here you can see how filling in the side faces makes the form feel somewhat flatter (the eye isn't necessarily sure if it's looking at weird shadows coming off a flat plane, or if it's a box), and if it does read as three dimensional, it does so in isolation from any surroundings. On the right side, however, the box features no internal edges but still reads as three dimensional entirely because of its clearly defined silhouette. The cast shadow then helps define the relationship between that form and its surroundings, making it feel all the more three dimensional.

So, with that laid out, I'll go ahead and mark this challenge as complete. Your work here is solidly done, and you've done a good job of laying out the constructions to feel solid and believable.