When looking at the wheel challenge, I mainly keep my eye out for a few different things. Is the student constructing the wheels properly, are they maintaining reasonable wheel-like proportions, are they abiding by the subtle degree shift and alignment to the minor axis, and lastly, are they capturing the textural elements (the tire treads, mainly) using the proper techniques introduced back in Lesson 2.

Usually the students fumble the last one, but honestly overall you've done a pretty great job across the board. Early on you've got some perhaps overly cylindrical wheels (most wheels swell a little more through their midsection, rather than remaining completely straight all throughout), but you caught onto this yourself and fixed the issue pretty quickly. Your proportions are probably the only element that are sometimes off throughout the whole set (still mainly focused towards the beginning, but 11 and 24 stand out as being longer than they probably need to be), but I'm really just nitpicking at this point.

All in all I'm very happy with your results. As nice it'd have been to have larger wheels, you're clearly working with a master ellipse template, and short of buying a hundred dollars worth of ellipse guides, we're stuck with this and that's totally fine. It is very nice to see a student actually focus on cast shadows as well, when dealing with their tire tread textures - although the ones where you've got especially large areas of solid black (12, 14, 16) do stand out somewhat more as though you're drawing either form shading rather than cast shadows (that is, putting your ink on the surface of the form in question, rather than putting it on the surface upon which the form casts its shadows), or perhaps you're just filling in negative spaces. Either way, remember that your ink's going to fall on a surface other than the form in question, and that shadow is going to relate to the form casting it. Meaning, we should be able to glean some information about the relationship between that textural form and the surface upon which the shadow it casts - like how high off that surface the form stands.

Here's a quick demonstration of what I mean about form shading vs. cast shadows, as I imagine the statement I just made may be a little confusing.

If you're uncertain about the whole "shadow tells us about the relationship between the textural form and the surface upon which it casts its shadow", think about how if you put a box on a tabletop, the size of the shadow it will cast will depend on the height of the box. The shorter the box, the smaller the shadow. The taller the box, the farther the shadow will reach. This kind of relationship is the sort of subtle information our subconscious looks for in a drawing in order to make sense of what it's looking at.

Anyway, like I said - your work here is really well done, so I'll go ahead and mark this challenge as complete. Keep up the good work, and good luck as you move onto the final lesson.