Jumping right in with the structural aspect of the challenge, you've done quite well. I'm pleased to see how thoroughly you've applied the ellipse guides (which I imagine wasn't the easiest, given that the more accessible master ellipse templates can limit us to much smaller sizes), and how where appropriate you did not merely flesh out the basic cylindrical structure, but included cross-sectional slices in the middle and even in between, to control the curving profile of the given tire to make it appear appropriately "inflated" (in the sense that it looks like it would land with a bounce) or more dense (like it would land with an unyielding thud). Different tires are made with different requirements in mind, so being mindful of how we can convey these differences matters a great deal. Nicely done.

I'm also pleased to see that you're mindful not only of the outward faces of the rims/spokes of your wheels, but also their side planes - and the fact that for the bicycle wheel you drew for number 15 you correctly determined that the right course of action was to draw those very thin spokes with two edges, as opposed to just as a single line each. Using two to enclose a shape (rather than trying to represent the structure with a single line) is the bare minimum we require to provide the viewer with information they can fully understand as being three dimensional, and this is actually something many students overlook when tackling this kind of tricky problem and having to decide between potentially making the structure thicker than it is in the reference, or undermining its solidity.

One point I did want to call out is that in some cases, like number 9, when drawing the rims, you opted to set aside the principles of markmaking introduced earlier in the course, and tackled it in a sketchier, somewhat more chicken-scratchy methodology. I understand that working in very small, cramped areas can be tricky, but it's important that when faced with a difficult problem, that we always stick to the core principles of how basic concepts - like markmaking - are to be tackled in the course as a whole. If the instructions don't explicitly allow us to deviate from them, we should still be striving to incorporate them even if we're afraid it'll undermine the result. At the end of the day, these are all just exercises. More broadly though, it seems that as part of this choice you also ended up skipping constructional steps (so where you might have drawn "through" the spokes to better understand how they sit in 3D space in relation to one another to make it all feel more solid and believable), which is also not the right call for this kind of problem. Just be sure to keep that in mind going forward.

Continuing onto the textural aspect of the challenge, this is where the challenge ends up serving as something of a trap. Basically students fall into one of three categories when it comes to how they approach the textural problems presented by the tire treads in this challenge:

• Some forget about the concepts relating to texture introduced back in Lesson 2, and end up trying to construct every single textural form present.

• Some remember that when we tackle texture, we do so with the intent of not drawing every single form, but rather leveraging the ability to imply the textures and letting the viewer's brain fill in the blank. Though they remember this, they don't necessarily remember the specifics of how we approach this in this course, and so they end up relying more on drawing what they see directly in their reference, rather than employing the specific methodology explained back in Lesson 2.

• And some - very few - remember the principles of texture as introduced in Lesson 2, and directly attempt to apply them. Not always as successfully as they'd hope, but with a clear intent to apply those concepts as they are explored within the framework of this course.

In your case, you fall into the second group. Where the first group tends to run into the problem of their wheels likely looking pretty visually detailed and engaging in isolation, but creating unintentional focal points which, through the densely packed detail end up drawing the viewer's eye whether they want to or not (making it very tricky to leverage control over the composition of their illustrations), in your case you definitely are in a greater position to control how the viewer's eye moves around a piece and experiences it, but you end up being very results-focused and end up skipping over how texture is meant to serve the core goals of this course.

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. These reminders specifically address a step that is somewhat missing or lacking in how you tackle these tire textures - you're leaning more towards copying what it is that's in your reference (with some modification to suit your needs, certainly) but are missing the focus on understanding the forms that are present, as they sit in 3D space. This is what matters most for our purposes in this course - we want texture to be just another instance where you're made to think through the relationships between forms in 3D space, and then to make choices (like the choices of how to design a given cast shadow shape, based on your understanding of the form casting it and the surface receiving it) based on that understanding.

As an extension of this however, getting more accustomed to this kind of thinking can be very useful even outside of the course by providing a more specific line of thinking to drive how we achieve that idea of "implying" detail, without drawing it all directly on the page. 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.

Implicit markmaking achieves this by being so fixated on drawing cast shadows instead of the forms themselves. 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 momentarily disregard maintaining a consistent light source for a given illustration (which is important, but like the bit about composition I mentioned earlier, outside of the scope of this course), this aspect of cast shadows and how the same form can ostensibly cast dramatically different cast shadows depending on where on the object it sits, gives us the freedom to dictate where we want to pack in lots of detail and contrast (which is usually a middling distance from the light source), and where we want to keep that contrast low (in the areas where all the cast shadows are so big they merge together into large complex shadow shapes due to the light source being very far away, or those where the light source is so close that all the shadows get blasted away entirely).

But it always comes back to understanding the relationships between the 3D structures themselves, because those inform the specific choices we make, in how we design the shadow shapes we draw. When we fixate on drawing what it is we see in our reference images, we end up designing less, and "painting" our textures on one stroke at a time. While this can achieve similar results, the approach itself affords us far less overall control.

Now, I've been writing at length about this, but you needn't worry about revisions - this challenge is presented and framed in this manner to give me the opportunity to revisit the textural concepts, to provide students with a reminder of what they involve, and to hopefully encourage them to revisit those concepts themselves before carrying forward. I will still be marking this challenge as complete, but I want to leave you with one last bit of advice.

When it comes to those tires with shallow grooves, or really any texture consisting of holes, cracks, etc. it's very common for us to view these named things (the grooves, the cracks, etc.) as being the textural forms in question - but of course they're not forms at all. They're empty, negative space, and it's the structures that surround these empty spaces that are the actual forms for us to consider when designing the shadows they'll cast. This is demonstrated in this diagram. This doesn't always actually result in a different result at the end of the day, but as these are all exercises, how we think about them and how we come to that result is just as important - if not moreso.

And with that, as promised, I'll go ahead and mark this challenge as complete.