Before I get started, I want to quickly note that there are a couple choices you made in how you tackled your work throughout this challenge that did puzzle me a little bit:

• Though the lesson material for this challenge stresses that it encourages the use of ballpoint over fineliners (it does so in bold at the bottom of the top section of the page, as well as in the homework section), you opted to use a fineliner. I believe I also called out this choice in your work for Lesson 6. In essence, you seem to have knowingly made the challenge harder on yourself, in a way that would not have made the exercise itself more effective. Your fineliners in particular do also appear to be slower to dry, so when using them it's important that you do so more patiently, to avoid having the ink smudge.

• I noticed some places where you used an ellipse guide (and I'm seeing a few different degrees, so while I can't be certain you were using the type of master ellipse template we recommend, it does appear to be so), but in many others you opted to freehand instead. The lesson material really stresses the benefits of using an ellipse template, so this is one of those cases where freehanding your ellipses was not the best of choices.

Anyway, jumping right in with the structural aspect of the challenge, overall you're handling it reasonably well. You're laying out numerous ellipses to build up the appropriate profile of your wheel (depending on the wheel, some demand a more prominent curve to their profile, with a larger central cross-section than the outer sides, to create the impression that the tire is more inflated, while others demand something more rigid and straighter). You're also being quite mindful of how to go about building out each of the structures of your rims/spokes, and are building them out in their entirety, rather than just focusing on the outward face. This consideration of the front and side planes of each such structure helps to make them feel more solid and tangible.

When it comes to the textural aspect of your challenge, you're falling in line with most - but that also means you're falling into the same trap most students do. That is, the trap of remembering that the concepts relating to texture as we explore them in this course has something to do with relying heavily on filled areas of solid black, but perhaps not digging as far into the past material to remember that our approach saves those filled areas of solid black for cast shadows only.

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 16 on this page, it looks pretty good floating in the void, all full of detail (the only thing keeping it from looking really excellent is that the placement of the individual tread chunks is more haphazard - investing more time into laying them out according to stricter planning points as shown here would definitely have yielded better results). 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.

Conversely, implicit markmaking leverages the fact that the shadows a form casts isn't always going to come out looking the same, depending on where it is on your structure. 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. For our purposes in this challenge we aren't even going as far as specifically worrying about where the light source is (although more broadly outside of this course, keeping your light sources consistent is beneficial) - we just need to know that we have reason to draw cast shadows differently, even if the form casting it is the same throughout. This gives us the freedom to control the density of our textures according to our needs, without changing the nature of the texture we're conveying to the viewer. At least, as long as what we're drawing is only the shadows our textural forms cast, and not the forms themselves.

The last thing I wanted to mention is regarding those cases involving 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.

Ultimately what we're doing when tackling texture in this course is just more spatial reasoning work. It's less about how closely we match the reference (in fact that's not really a direct consideration at all), and more about the puzzles this forces our brains to solve as part of the exercise. It requires us to think about what kind of shadow a form would cast, based on how it occupies space, and how it relates to the surfaces around it - something that is not remotely easy to do without first drawing the form itself. Ultimately when evaluating your own work for this exercise going forward, keep that in mind, and try not to be distracted by the superficial matters of how it matches the reference.

Anyway, keep that in mind. As this trap was an intentional thing, just take it as a sign to reflect on what sections of the course you may have similarly allowed to fall through the cracks, and review them accordingly (starting with the texture material for Lesson 2). I'll go ahead and mark this challenge as complete.