Normally when I critique these wheel challenges, I'll critique them in two sections - first the structural elements, then the textural ones. Here however, you've by and large done a really good job across both, and the main issue that I want to address comes up in both the structure and the texture. So, we're kind of going to lump them in together - although first we're going to talk about your strengths in both categories.

Structurally speaking, you're very mindful of the nuanced elements of the objects you're constructing - from ensuring that you're using multiple ellipses to create a smoother, arching profile and create the impression of a tire that is inflated and would land with a bounce, rather than a heavy immobile thunk, to defining the side planes of the rims/spokes to ensure that they're given a sense of thickness. In terms of texture, where most students end up totally forgetting about the concepts from Lesson 2 (this challenge itself is a trap laid to help give them a rude reminder that they should review that material), you have not. While you haven't approached texture entirely correctly as far as what's explained in Lesson 2, you have clearly been thinking about each individual textural form one at a time, rather than trying to create a more general "impression" of a texture purely through observation and the direct transferrence of visual detail. You're actually taking the time to think about how those textures exist in 3D space.

So, the main issue that is shared across both? It's what's illustrated here. What you're doing is on the left - you tend to fill in the side planes with solid black - where what we want is on the right, where the filled areas of solid black are reserved only for cast shadows. Filling in the side planes is more akin to form shading, where the orientation of the plane dictates whether it should be lighter or darker. What we're after here is specifically creating new cast shadow shapes that define the relationship between the form casting it and the surface receiving it, through the design of the shape itself. Once outlined, we can then fill it in. If you catch yourself filling in a shape that already exists, then take a step back and think about whether what you're drawing is actually being cast as a shadow. Same goes for if you find yourself tempted to use hatching - that's a good sign that you're leaning into form shading, which as discussed here isn't to be employed in this course.

The reason this is significant is because filling in those side planes still has a lot of the same downsides as outlining every textural form (in terms of being explicit markmaking). Because we're technically still drawing the textural forms directly, we're locking ourselves into having to either draw every textural form, or to have the transition to where we stop defining as much of them appear somewhat strange and jarring. Instead, as shown here on this example of bush viper scales, whether we decide to apply lighting that blasts those cast shadows out, or makes them larger and deeper, it's not the forms that are communicated as being present along that surface which changes - just which ones we're able to see. It disconnects what's drawn from what is conveyed.

So! Be sure to keep that in mind, but everything else is coming along great. I'll go ahead and mark this challenge as complete.