This challenge breaks into two distinct parts. First we look at the overall construction of the wheels/rims/etc, then we look at how you handled the tire tread textures.

Starting with the construction, I see that you ended up working freehand for these. All things considered you definitely had some where the ellipses came out especially well (particularly towards the beginning), but there were definitely areas where this choice definitely increased the overall complexity of the task at hand, inevitably distracting you from the core of the challenge. It's completely understandable that not all students can get their hands on ellipse guides, in which case freehanding is really the only option - but sometimes students choose to freehand them thinking that doing so will make the exercise more effective.

Just in case you're in the latter group, I do want to reiterate that we recommend the use of certain tools in certain circumstances to reduce the number of problems the student has to face all at once. This allows them to focus more strictly on the specific issues at hand, making the exercise more effective. If you did try getting an ellipse guide but found that full sets are too expensive (they can definitely get quite pricey), most students actually use the more limited "master ellipse guides" which provide a range of degrees but only go as big as maybe 1.5". Despite this, they are still very useful for this challenge and throughout Lesson 7, and are worth picking up - and of course they're much more affordable than a whole set.

Of course, if you tried looking for them and weren't able to find any, then that's entirely fair.

Anyway, circling back to your work, a lot of these did come out quite well, and you're definitely quite well practiced with freehanding your ellipses - mainly cases where they came out especially uneven did seem to be one-offs (probably where you stumbled and didn't engage your shoulder correctly, or whatever other kinds of mistakes that sometimes just happen). I do wonder however whether the additional effort required for the execution of these ellipses may have caused you to draw fewer ellipses overall, even if a particular construction may have benefited from more of them.

The more ellipses we cram into the ends of the basic cylinder, the better we can achieve the sort of "beveled" appearance that creates an impression of an inflated structure. If you look at number 5 for instance, you get a little bit of a sense of inflation with the middle ellipse being larger, creating a sort of bump through its profile, but conversely, number 8 serves as an excellent example of how we can create a gradual curvature in its profile to achieve a smoother result that feels like it would have a bit more give to it. Of course, the more ellipses you have to draw, the more opportunities there are to make significant mistakes, and some people would be a bit nervous to do so.

The other constructed structures - like the spokes, rims, hub-caps and even gear-teeth in some cases - were all constructed quite well. You showed a good sense of how to build them on top of the existing structure, as well as a keen eye for spacing them out appropriately.

It is worth calling out that 19 got a little wonky, due to the far end being drawn with a narrower degree than the end closer to the viewer (far end should always be wider), but this was obviously just a one-off mistake rather than a pattern born of misunderstanding.

Now, the other section of this challenge comes down to texture, and for the most part you've actually avoided falling into the trap I set out for students. For most students, at this point it's been ages since they last looked at the Lesson 2 section for textures, and as a result many of them end up trying to tackle the tire treads by using explicit markmaking techniques and constructional methods. You, in many cases, correctly employed cast shadows to imply the presence of your textural forms.

There definitely were some places where you confused cast shadows and form shading, opting to fill in the side planes of a given form. As shown here, filling in the side planes actually creates a flatter impression where it separates the form itself into that top face (a flat plane) and the areas that were filled in. Casting the shadow onto surrounding surfaces keeps the form cohesive and complete (and still maintains the illusion that we're looking at a 3D form even when internal edges are omitted, due to the way the corners of the silhouette imply their presence).

Sometimes this mistake came up in areas of texture (a random example would be 19, where each of the gear's teeth has a face filled in), as well as with larger constructed areas, like how in 11, 12, and 13 you filled the interior faces as shown here. The key thing to keep in mind is that when drawing any cast shadow, we need to be consciously aware of the nature of the specific form casting it, and the specific surface receiving it.

Something that can help to force yourself to think about that is to purposefully draw all your cast shadow shapes in two steps - first outlining the intended shape, then filling it in. If you catch yourself thinking, "oh the shape is already there!" then you're probably about to fill in an existing plane or space, and need to consider exactly what you're doing a little more closely. Sometimes it's fine - there are plenty of situations where the entirety of the shadow being cast will fill in a space, and we see this often when shadows are being cast into a hole or a groove. It does have to be thought out, however, and given adequate consideration - this leads to the subtle differences (or their absence) between just arbitrarily filling things in, and actually thinking through the relationships between forms.

Anyway! Overall, you're still doing well. I would still recommend getting a simple master ellipse template, but ultimately it's up to you to determine whether that's possible. Either way, Lesson 7 is extremely demanding, and taking any steps you can to avoid further complexity will help you focus on applying and learning its concepts as effectively as possible.

I'll go ahead and mark this challenge as complete.