Starting with the structural aspect of the challenge, I can see that you ended up freehanding your wheels instead of using an ellipse guide. While I assume the reason for this was that you weren't able to get your hands on an ellipse guide, but all things considered you managed the freehanding better than most I've seen. In general, using the ellipse guide is definitely far and away what I would recommend (even the master ellipse guides which have limited size options and usually result in smaller wheels), the main point is that it frees up our mental resources to focus on the core elements of the exercise. While you did a great job building these out, I expect it probably took a ton out of you.

If you ended up skipping over the ellipse guide due to the fact that the wheels would just end up being very small, I'd still strongly recommend using one when you get into Lesson 7, specifically for the "constructing to scale" approach we use to build out unit grids. Having a reliable ellipse guide helps a ton with this, and freehanding - even for those who are quite good at it - just isn't the best idea if there are other options.

Anyway - you've built out the wheels well, and I'm glad to see that in most of these you've included a bit of a widening through the midsection to help convey the "inflated" nature of the tire, so that it would land with a bounce rather than a heavy thud. I'm also very pleased to see your attention to the structure of the spokes of the rims. Sometimes students will focus more on drawing the outward faces of those spokes, but neglect to define their side planes, causing them to come out quite flat. Yours are beefy and solid, great stuff.

Carrying over onto the textural aspect of the challenge, this bit is something of a trap. It's very common for students to simply be so far removed from Lesson 2 and its concepts, and to perhaps not have continued reviewing old material or not as consistent in including that section into their warmups, that they simply forget that we ever discussed the concepts of implicit vs. explicit markmaking, and the importance of conveying texture not by drawing the textural forms directly, but rather by drawing the shadows they cast. This is certainly a trap you've fallen into yourself.

By and large, you approached the tire tread textures by outlining either the chunkier protrusions (like number 10, where each form was completely drawn, with their visible edges being defined), or the shallower grooves. While the distinction between drawing the chunkier protrusions vs. implying them by the shadows they'd cast (in which case we'd design cast shadow shapes not from observation, but rather by leveraging what we've observed to understand the relationships in space between the given form and the surfaces around it as explained here) should be something you can simply go back and review, the case involving shallower grooves can be a little more tricky.

Basically, grooves, holes, cracks, and other such textures where the name we'd ascribe to it doesn't actually refer to the textural forms but rather a negative space, or an absence of form, it's very easy for students to think of them as the textural forms they're meant to be conveying. As explained in this diagram, it's actually the structure around these holes and grooves that are the forms in question, and so we need to be focusing on how they cast shadows upon one another. While you mainly focused on outlining the grooves here, many other students fill them in completely - which is still wrong, but the difference in the result can be pretty subtle. Really it comes down to how we're thinking about the problem as we address it - whether we're actually thinking about how these things sit in 3D space, and how they relate to the structures around them, or if we're just focusing on observing our reference and carrying it over into our drawing without taking the time to understand it further.

Of course, like I said - this is an intentional trap. So, rather than holding students back over it, I simply leverage it as a good reminder that there may be things you've allowed to slip through the cracks, which haven't received enough attention, and so this is a great opportunity to go back and review that material prior to moving onto Lesson 7 and completing the course. So! I'll mark this challenge as complete, and will leave you to review that material.