So this challenge basically serves a couple purposes. Firstly, it allows students to get comfortable working with ellipse guides, and also works as a sort of microcosm of the challenges faced when drawing cars - since every different kind of wheel/tire has its own character to it, and it can be quite challenging to pin it down in its specifics. Here we get to deal with them in smaller, more focused ways, before we jump into the more complex cars later on. Of course, this part is pretty obvious.

The other reason for this challenge is a trap. Almost every student this deep into the course will have forgotten some of the particulars of what was discussed way back in lesson 2's texture section, and a pretty significant majority of them have reverted back to outlining their textural forms, and otherwise working using explicit markmaking, rather than implicit.

So, as far as wrist-smacking goes, that's what I have to work with, and unfortunately you have (for the most part) passed on both of these tests. I'm not sure whether to offer my congratulations, or condolences, but there will be no beating today. You've done an excellent job building out your various wheel experiments, capturing that subtle swelling through the midsection to establish the "inflated" nature of the structure, and your attention to construction carried over into the spokes/rims as well. You didn't cut an corners - you built them out with a clear grasp of how they all exist in 3D space, and took your time as you built out each spoke, and even as you spread them across their space.

When it comes to the tire treads, you jumped right in with clear attention to working with filled shadow shapes, working implicitly and not outlining any of your textural forms. I laid a trap, but you jumped right past it. I really have just one criticism to offer, and there are only a couple places where it becomes more prominent.

If you look at wheel 22 (the water-wheel type thing) and wheel 09, you appear to be using your filled black shapes to draw the side plane of the big form, rather than capturing the shadow it casts. I'm actually not completely sure whether this is the case with 09 (it could go either way, and the ones on the farther side of the wheel are definitely cast shadows), but on 22 it's very clear. You're filling the face, basically capturing form shading, rather than drawing the shadow it would cast on its surroundings.

This is a very common mistake, but there are plenty of cases in your set where you don't make it. For example, with 13 and 14, you're definitely thinking about how they cast shadows on their surroundings. So, it's clear it was just a little slip-up, rather than something you misunderstood. All the same, I figure I should share this little diagram which shows the difference between capturing cast shadows and filling a side plane. The key difference is that when we capture cast shadows, we ensure that the silhouette of the textural form that we imply includes corners that help suggest the presence of different planes, rather than just that top one.

Anyway, you've done a great job. I'll go ahead and mark this challenge as complete. Keep up the fantastic work.