Starting with the structural aspect of this challenge, you've definitely put your ellipse guide to good use. I understand that the sizes can be quite limited (although honestly you managed to have some pretty large ones all things considered), but this is entirely expected and at least until we're able to start selling our own cheaper ellipse guide sets (which we are getting closer to, as we've been doing a lot of the preliminary work on it and have acquired a laser cutter), it's definitely the norm.

Using your ellipse guides, you did a great job of building out the core structures beyond just a basic cylinder, but including a number of intermediary ellipses to create a gentle arcing profile, to help capture how the wheels themselves have inflated tires, which would land with a bounce rather than a heavy thunk. You've also done a great job with your spokes/rims, where you've not only established the outward face, but you also were sure to include the side faces of these structures, helping them to appear three dimensional rather than flat. To that point however, while you generally left these side faces empty, I did notice that here you opted to fill them in. This relates more to form shading however, which as discussed here should not play a role in our drawings for this course. In this case especially, it tends to split the form into two parts - the flat outward face, and the side planes, which the viewer will usually first expect to be cast shadows rather than more structure.

Continuing onto the textural aspect of this challenge, the challenge itself is designed as something of a trap. It's pretty common for students outright forget about Lesson 2's textural principles, as a result of simply being so far removed from it. There are certainly ways in which you've fallen into this trap, although I can see a variety of signs that you are at least trying to consider how to apply elements of those concepts, albeit with issues.

Our tires here fall into a couple main categories - you've got those with shallower grooves, and those with chunkier protrusions. It's easier to get away with purely explicit markmaking (drawing the grooves themselves with lines), although I can see some cases like this one where there was certainly consideration to implying the presence of forms, rather than drawing the grooves directly.

That said, it's very easy for students to fall into the trap of thinking that because the grooves or holes of a texture are the thing we're referring to by name, with proper nouns to label them, that they are the textural form in question, and thus they're the things we're drawing. Of course, that is not the case - holes and grooves are an absence of space, and the walls that surround them are the actual textural forms in question, which cast shadows upon one another and onto the floor of the hole. This can result in a very small change in how we draw the texture (or even in some cases no perceptible difference), but the manner in which we think about these textures still matters a fair bit. These notes get into more detail on how to think about dealing with grooves and holes.

It is definitely a lot easier to identify whether a student is actively working implicitly or explicitly when dealing with the second category, with chunkier textural forms that protrude farther from the surface of the object. Reason being, to capture them implicitly would mean to primarily suggest their presence by drawing the shadows they cast (aside from where they break the silhouette of the core object, where we'd still use outlines).

Drawing the textures implicitly, and more specifically implying the presence of those big textural chunks, has us drawing the shadows they cast, and not actually drawing the forms directly. The reason for this is that while these wheels look fine floating here in isolation, the densely packed linework can create an unintentional focal point if these wheels were used as part of a larger vehicle construction - drawing the viewer's eye whether you want it to or not, and impeding your ability to actually guide the viewer's gaze through a composition.

Conversely, working implicitly as shown here in this example of an african bush viper's scales, allows us to control the manner in which we actually convey the textural forms (in terms of how much ink we want to use), without changing the nature of the texture itself. We can choose to work with heavy, expansive cast shadows, or with very slight ones, and still convey effectively the same information.

Not to worry - the challenge is designed to highlight this point, as something of a rude reminder that one might want to review that material before moving onto the next lesson. So, I will be marking this challenge as complete. I did however also want to offer the following: this diagram (and this one which is the same thing but slightly different, in case that speaks more clearly to some students) illustrates, more in relation to the texture analysis exercise, how the cast shadows actually work. This diagram demonstrates a similar idea, but more directly being applied to the texture analysis.