Jumping right in with the structural aspect of the challenge, you certainly did well considering that you ultimately ended up freehanding them. I'm assuming that you tried to get your hands on a master ellipse template (as heavily recommended by the lesson material), but ultimately couldn't. All told, I am still pretty pleased with how you built out your wheels' structures, and how you handled more complex aspects like getting the wheels to widen through the midsection, or to have sides that are more beveled.

That said, I do think that as a result of the inherent sloppiness that comes from relying on freehanded ellipses for something like this, it definitely did impact how much you were willing to stick to the principles and concepts of the course in other areas - for example, when constructing the spokes of your rims. As we can see here, your linework isn't especially solid - individual strokes are fairly smooth, but you frequently break marks up into different strokes, are not applying the ghosting method at all, and are by and large falling short of what we know you're capable of. This isn't actually entirely unexpected - when there's sloppiness on the page, it subconsciously can be interpreted as permission to continue to be sloppy, and to disregard the things we know in favour of getting through the work faster. It does however speak to how mindful you're being of your choices however, and whether you're really forcing yourself to be hyper-intentional about the choices you're making. Ultimately that is very important for the goals of this course - we want to develop our instincts, so that outside of this course we can rely on them to do a lot of the heavy lifting, freeing up our conscious brain to focus on what it is we wish to draw, rather than how. But that is only achieved by being more intentional when doing the assignments within the course. Using our instincts to train our instincts only results in a mess.

That's not to say you leaned into the sloppiness in every case. There were certainly others that were better structured and followed our principles of markmaking more closely, but when such things are not consistent, it does imply that there is room for improving one's approach to make it more consistent.

Continuing onto the textural aspect of the challenge, this part is something of an intentional trap. Being as far removed from Lesson 2 and the textural concepts it covers, it's very common for students to remember that the marks we're working with when engaging withh texture involve a lot of filled black shapes, but to forget about the specifics of what those black shapes are meant to represent, without going back and reviewing that material. Other students will go further, forgetting about the concepts of implicit markmaking and our use of filled black shapes altogether, and instead opt to try and use line and explicit construction to approach all of their tire tread textures, which appears to be the route you opted for.

When it comes to texture specifically - at least, how we handle it here, which is very specific to this course and what it seeks to develop in our students - we are ultimately looking at the same kind of problem that the course as a whole explores: spatial reasoning. We imply the marks we draw (you can refer to the implicit vs explicit markmaking section for more specific information on this) by drawing the shadows our textural forms cast on their surroundings, not by drawing the forms themselves (in terms of outlining them, or otherwise drawing anything about the form itself). It's the shape of the shadow itself, which is designed based on our understanding of the relationship in 3D space between the form casting it and the surface receiving it. And so, as stressed in these reminders, in this course we're never just drawing what we see. We're looking at our references, and understanding what they tell us about the forms in question, and then deciding on how to convey the relationships between them in space.

The reason we use implicit markmaking instead of explicit is fairly simple, although it's not always obvious. For example, looking at any of your wheels like number 14 on this page, it looks excellent floating in the void, all full of detail. But when it becomes part of an existing drawing, all of that packed detail can actually work against you by drawing the viewer's eye to it whether you want it to or not. This interferes with our ability to control composition (which is all about dictating how the viewer experiences a piece, what they look at and in which order), which while outside of the scope of this course, is still something I want to give students the tools to engage with more easily.

Explicit markmaking basically locks us into an agreement with the viewer: whatever is drawn is present, and whatever has not been drawn, is not present. And therefore to convey each textural form, we have to declare its presence explicitly. Implicit markmaking on the other hand gives us more freedom by disconnecting the marks we draw from the specifics of what is present.

It achieves this not by picking some arbitrary visual element and fixating on that. Rather, the cast shadows we rely on as the basis for implicit markmaking actually works off a physical reality. As shown in this diagram, depending on how far the form is from the light source, the angle of the light rays will hit the object at shallower angles the farther away they are, resulting in the shadow itself being projected farther. Even if we set aside the matter of maintaining consistent light sources (which is important, but not relevant to the scope of what we're dealing with in this course), this gives us a basic premise to build off: that the same form, depending on where on the object it is placed, will cast shadows of different sorts - some big, some small, some occluded by the form itself as to be invisible. This gives us an amount of control over how visually dense a drawing must be in order to convey the desired elements to the viewer.

So! I am of course going to be marking this challenge as complete - you fell into a trap I set, after all - but take it for what it is. A reminder that when going through a course this long, it is inevitable that you will forget about certain things, and that some concepts may fall through the cracks. Take some time to reflect on what might merit reviewing (starting with the texture material, for which these reminders serve as a good re-entry point, but you may want to think about whether there might be other concepts that merit similar review).