Good lord, these are beautiful. While aesthetics isn't strictly one of the factors I critique by, it's hard to ignore the fact that these wheels just plain look great. They'd be at home on any DC or Marvel comic page.

But anyway, onto the critique. Starting with the structural aspect of the challenge, you've knocked it out of the park. You've leveraged that ellipse template set you've got to great effect, including nice, often very subtle arcs in the wheel's profile to get that nice, "inflated" appearance for the tire. You've also done a great job of making your rims/spokes feel solid in how you've fleshed out both their outward face, as well as their side planes. So, full marks on that front.

As to the other section of the challenge - texture - here you didn't fare quite so well. This challenge is, by design, a trap. Given how far removed we are from Lesson 2, it's very common for students to have forgotten much of what we discussed in regards to cast shadows and implicit markmaking. You certainly stepped into the trap, so let's take a moment to talk about it.

When it comes to tackling your tire tread textures, yours fall into a few categories. You've got the ones where you just outlined the textural forms just as you would any other form, applying explicit markmaking across the board. This puts us in dangerous territory when our wheel becomes part of a larger scene, becoming an unintentional focal point, and drawing the viewer's eye whether you want it to or not.

Then you've got the ones where you filled in the side planes of those textural forms, like in 3. This unfortunately is more akin to form shading, where the side plane is either lighter or darker based on its orientation in space. Cast shadows are actually a new shape designed based on the relationship between the form casting it and the surface receiving it - as opposed to an existing plane/shape that is merely being filled in. The thing is, they can look very similar. I've got this explanation I've been pasting from an earlier critique, along with a diagram, that may help illustrate the point.

Here'the diagram and here's the explanation:

In the top, we've got the structural outlines for the given form - of course, since we want to work implicitly, we cannot use outlines. In the second row, we've got two options for conveying that textural form through the use of filled black shapes. On the left, they fill in the side planes, placing those shapes on the surface of the form itself, and actually filling in areas that are already enclosed and defined on the form and leaving its "top" face empty. This would be incorrect, more similar to form shading and not a cast shadow. On the right, we have an actual cast shadow - they look similar, but the key point to pay attention to is shown in the third row - it is the actual silhouette of the form itself which is implied. We've removed all of the internal edges of the form, and so while it looks kind of like the top face, but if you look more closely, it has certain subtle elements that are much more nuanced - instead of just using purely horizontal and vertical edges, we have some diagonals that come from the edges of the textural form that exist in the "depth" dimension of space (so if your horizontals were X and your verticals were Y, those diagonals come from that which exists in the Z dimension).

Now while this third category doesn't appear in your work, I did still want to take a moment and explain it. It is where the student merely fills in the grooves with black. We can often see this with textures consisting of cracks or holes. Reason being, we end up focusing on the thing we can name - the hole, the crack, the groove - as being the form. But it is in fact the walls around it that cast the shadows. The hole is just a negative space, an empty thing, encased in walls and a floor.

Here's another diagram to help illustrate this point.

Anyway, worry not - as this is an intentional trap to scare people into remembering to review their textural concepts, I do not hold it against you. You and your beautiful wheels are free to go. You may consider this challenge complete.