So this last chunk of the course - starting with lesson 6 - are areas where the use of an ellipse guide, even a more limited 'master' ellipse guide that includes different degrees but at smaller sizes, is highly encouraged simply because it eliminates one area where students are expected to have plenty of room for improvement. By eliminating the challenge of drawing ellipses, we can focus on the other aspects involved in constructing wheels. Since you opted to freehand your wheels, I won't be pointing out areas where your ellipses need work, beyond stating that they certainly do weaken your results a fair bit.

From what I can see, as far as the construction goes you're applying the steps correctly - building out multiple ellipses, widening your degree, and drawing through them. I noticed a few places where you apparently used pencil (like 18 and 19) - you should at this point know that you should only be using the tools permitted in the assignment. If, as in 18, you feel drawing lines out from the center of the wheel is beneficial to your construction, then you should do so in ink. There's no real benefit in doing it in graphite unless you're focusing on the end result over the process, which of course would be misguided. Remember that every drawing throughout this course is an exercise, and nothing more.

There are definitely areas where you approach the rims of your wheels more effectively than others (6 is fairly well done, for example, whereas 18 comes off as rather flat and cartoony), and you outright leave the rims out for a number of these. I wouldn't really consider those to be complete.

Moving onto the tire treads, what stands out most is actually pretty common, and it's one of the reasons I put this challenge in this position in the course - students tend to forget about what they learned about texture from Lesson 2. Or at least, they forget about important parts of it. For example, there are a lot of tire treads here where you draw your textures purely through line. Line itself isn't terribly useful when dealing with texture, because as shown here it tends not to allow for much dynamism. There's a bit of variation in line weight, but that's about it. Instead, we want to focus primarily on the use of shadow shapes, which can vary more significantly. We achieve those shadow shapes by purposely approaching our textural marks using the two step process described here - first outlining our intended shadow shapes, then filling them in.

When it comes to tire treads with significant protruding 'chunks' (like 16, 13, 11, etc.) make sure that you approach them using the implicit techniques we talked about back in lesson 2, rather than attempting to outline them explicitly and construct them in their entirety. Drawing implicitly means capturing the shadows they cast on their surroundings. Those shadows are things we can adjust and control depending on how densely we want to capture those textures - by changing the cast shadows, we don't alter the specific nature of the texture, just how it is represented. If instead we use explicit drawing techniques as you've done here, we get 'locked in' to a specific density of linework which can create unintended focal areas, and draw attention from the viewer where we don't actually want it to be.

All in all, I'm kind of on the fence with this submission. This isn't generally an exercise where I assign revisions, because it's not generally productive. One of the biggest factors here is that your ellipses are definitely making this exercise more difficult than it needs to be, and based on the strength of your previous work from lesson 6, I know you're fundamentally capable of better. Getting an ellipse guide would definitely help with that, and this will be the case for the next lesson as well. Please looking into getting one, if at all possible. If not, you are going to have to put considerably more time into every mark you draw.