Jumping right in with the structural aspect of the challenge, you've done a fantastic job here. The core cylindrical bodies come out feeling solid, and I'm pleased to see the widening through the midsection to create that sense that the tire is inflated, that it would land with a bounce rather than a heavy thunk. You've also generally done a great job of minding both the outward faces as well as the side planes of the spokes/rims in the center of the wheel. One thing I specifically look out for is whether the student is taking care when defining that side plane - you generally did with cases like numbers 12, 15, 24, among others demonstrating this well. In number 17 however, I did notice that you got a little sloppy with the side planes. As shown here, in areas where we'd be able to see the side plane's intersection with the inner tube of the wheel structure, you didn't quite define that intersection as clearly as you could have. This was clearly a minor lapse, once out of 25, so I'm not particularly concerned about it. Just calling it to your attention so you're aware.

Carrying onto the textural aspect of the challenge, this part of the challenge is essentially a little trap to check if the student has continued striving to apply the concepts from Lesson 2's texture section, or not. Being as far removed as we are from that material, it's actually very common for students to forget it entirely and end up trying to establish their textural forms through purely explicit markmaking, using constructional drawing tools.

In your case, you didn't fall into the trap entirely - I can clearly see that you've attempted to imply the presence of your textural forms, which is wonderful. Where this can be done better however is in that you're largely trying to use lines - that is, individual strokes - to define your shadows. So in effect, your tire treads are all suggested by having part of their outlines drawn. This is not the same thing as drawing a shadow however, as shadows aren't just edges or lines. They're entire shapes, and it's the specific design of that shape that allows us to convey the relationship between the form casting the shadow, and the surface receiving it. You can read more about this here: https://drawabox.com/lesson/2/2/reminders

Working with line over shadow shapes can also put us in a position where we may be thinking more in terms of the mark representing the shading on the side plane of the textural form. This would however be incorrect, as form shading (which as discussed here we try to leave out of our drawings for this course) is technically a type of explicit markmaking, where we're still technically drawing the textural form rather than implying its presence by merely drawing the shadow it casts. This locks us into having to draw every single textural form (otherwise it'd look like sections were missing), whereas implicit markmaking hinges on disconnecting what's specifically drawn, or how it's drawn, from what's represented.

In other words, let's say you have a texture made up of bricks. If we drew this using explicit markmaking - either by outlining each brick completely, or by filling in their side planes to give the impression of shading (where surfaces pointing towards the light are left white, those pointing away from the light are filled in with black) - every brick drawn would tell the viewer "there is a brick here", and every brick not drawn (like you'd often see in drawings where they don't actually draw every individual brick) would read as being a bald patch on the wall.

What we want of course is to say "here's some bricks, take this information and assume the whole wall has bricks even where I haven't drawn them". We can achieve that when working with cast shadows because of the fact that cast shadows are subject to the relationship between the light source, the form casting the shadow, and the surface receiving it. Depending on where the texture is relative to the light source, it'll change the nature of the cast shadows - and the forms that are closest to the light source, being hit by the light at a steep enough angle (as shown here in this side-view of our texture analysis exercise, where the light source is at the far right, resulting in a steeper angle for the forms closest to it and a shallower angle producing longer shadows for those far off to the left), will end up with shadows so small they might even be imperceptible at a distance.

Because this variable exists - that lighting changes the behaviour of the shadows without changing the relationship between the textural form and the surfaces around it, this gives us much more freedom to stylistically decide, in our own work, where we want our shadows to be cast and where we'll leave them to be implied.

Anyway, that was a bit of a lengthy explanation but hopefully it made sense. All in all, you're still doing very well, just be sure to work with shadow shapes rather than individual lines when approaching any textural work for this course. I'll go ahead and mark this challenge as complete.