Jumping right in with the wheels' construction, by and large you've done a pretty great job with this. I did notice a bit of weirdness when it comes to the degree shift from one end of the wheel to the other - it looks like you're working with the same ellipse, but I can only assume that this is due to a fairly limited ellipse guide. I'm mentioning it in the slim chance that it was intentional, but I can completely understand the limitations we may have to work with, and I am still pleased to see that you chose to work with an ellipse guide.

Another point I often look for is whether the student is drawing each individual spoke from the rims, and whether they're considering the side planes of those spokes alongside the more prominent face. I'm pleased to see that you were fairly meticulous in that area, with the only spots you took a bit of a shortcut being the bike wheels at number 4 and 8, and right by the end at 23. For the bike wheels, that was very clearly intentional - generally I would avoid representing a form as a simple line. If at all possible, give it the slightest of a pair, even if they're only a little ways apart. It's still enough to make the difference and give that spoke a greater sense of form. As for number 23, I think you may have just gotten a little excited, and slipped up in an area in which you otherwise knew better.

With construction out of the way, now we can talk about why this challenge is something of a trap. See, we're nearly at the end of the course, and we're ages away from the early days of Lesson 2 and its section on texture. Unfortunately, you did indeed fall into that trap - but don't worry, it's largely expected.

It serves as a reminder for students to review that material. There are some pretty important reasons why we can't rely so heavily on outlines and explicit markmaking for everything. These wheels look just fine individually, floating in the void, but when you actually use them as part of a vehicle, all of a sudden there's two or more of them, they're smaller so that linework is more concentrated, and all of that contrast is drawing the viewer's eye right to the wheels whether you want it to or not. When it comes to picturemaking in a larger scale, we have to be able to control how the viewer's eye travels around a page, and therefore where those focal points are. We need to be able to choose to take a tire and still convey enough of its tread as is necessary, but while controlling how much attention it draws independently of that.

That's what implicit markmaking does, and you can see it in action in this example. It's not of a tire (it's african bush viper scales), but it's the same idea. We can convey the same specific forms but with less ink, or with more.

So! I'll leave you to work on that yourself. As the trap was intentional, you won't be assigned revisions for it. You may consider this challenge as complete.