Starting with the structural aspect of the challenge, you seem to have initially have had some trouble aligning your ellipses, but that quickly gave way to some fairly solid constructions. I'm pleased to see that you've been using ellipses of different sizes to flesh out the curving profile of your wheels as needed, which helps to create the impression of tires that are more inflated, which would land with a bounce rather than a heavy thud.

I'm also pleased to see that you've been mindful of constructing all of the different planes of your wheels' spokes/rims - it's easy to focus only on the outward faces, but this leaves the structure feeling quite flat. In ensuring that the side planes were included for those relatively small structures, you did a great job of making the whole thing feel real and tangible.

Carrying over onto the textural aspect of the challenge, this is a portion that is left as a bit of a trap. Being as far removed as we are from Lesson 2, it's pretty normal for students to just... forget to practice the textural concepts going forward, and so when faced with the tire treads here, they tend to panic and just draw them however they can (which usually means using explicit markmaking techniques instead of implicit ones).

I am pleased to say that you did not fall into this trap - and given that we fully expect students to do so, so we can use this as a reminder to review any material the student may have allowed to slip through the cracks before finishing up the course - that's pretty impressive.

There certainly is room for improvement (and this will come from continuing to develop your spatial reasoning skills), but I can see quite clearly that your intent in drawing those filled areas of solid black (in most cases) are driven by identifying the textural forms that are present, and considering what kind of shadow shape they would cast on their surroundings. That shape defines the relationship, and so taking care to design it intentionally helps a great deal, and I'm seeing a fair bit of that here.

I can see that 14 was something of an outlier, where you broke away from that approach to conveying textures - but the reason is pretty clear. That structure didn't really have any noticeable texture to it (it appears quite smooth), and so you didn't really have anything to cast shadows. In this case, it's fine not to draw any filled areas of solid black. Always remember that those shapes come from texture that we wish to convey to the viewer - if no such texture exists, there's just nothing to draw there, and it's best to leave it blank to convey that smoothness. What you did here was shift to something more akin to form shading, which as mentioned here in Lesson 2 isn't something we concern ourselves with in this course.

So! I'll go ahead and mark this challenge as complete. Keep up the good work.