Starting with the structural aspect of your wheels, you've done quite well. While freehanding certainly put you at a disadvantage (and I will always stress that the allowance of using an ellipse guide is not a kindness - it's to specifically help students focus all of their mental energy on the core focus of the exercise, without committing some of it to executing their ellipses as desired) you've largely handled it quite well. I'm pleased to see that you're mindful of achieving a curving profile to your wheels, which helps to capture the sense that the tire is inflated, rather than solid all the way through, and that it would land with a bounce rather than a solid heavy thunk.

You've also handled the spokes of your rims quite well in most cases, establishing not only the outward face of the spokes but also their side planes, so as to establish them as solid forms. The only circumstance where I felt you fell a little short on there was with wheels like number 20 - although I can understand why. Bike spokes are very thin, but all the same it's important not to allow our forms to be reduced to singular lines, as they have little capacity of being interpreted as 3D structures. It's better to err on the side of making them a bit thicker - at least for our purposes in this course, where each drawing is an exercise, meant to develop our spatial reasoning skills.

Continuing onto the textural aspect of the challenge, you've by and large fallen into the same trap that most students do at this stage, and at this point it is largely by design. We're far enough removed from Lesson 2 that most students forget the principles of implicit markmaking versus explicit markmaking, the use of cast shadows, and so on, and so this challenge serves as a good (albeit somewhat rude) reminder that it's important to review that material before finishing up the course.

You do end up using explicit markmaking, effectively constructing those protruding tire tread "chunks" in order to establish how they sit in space. You certainly do then go on to incorporate filled areas of solid black, but the opportunity to merely imply those textural forms has already passed once those forms have already been drawn. Furthermore, in cases aside from wheel 7, you usually go for filling in the side planes of those forms, which is more akin to form shading (since we're dictating that a given surface will be lighter or darker based on its orientation in space, whereas a cast shadow involves understanding the relationship between the form casting it and the surface receiving it, and will generally require us to design a new shape to define that relationship rather than simply filling in one that already exists).

The reason that explicit markmaking is not always an effective tool for every task is that it locks us into a very dense amount of visual detail. This can be fine if we're looking at wheels floating in the void, but when we use them as part of a larger vehicle, they become focal points, drawing the viewer's eye to them whether we want them to or not. This severely limits our ability to guide the viewer's eyes through a piece.

Conversely, implicit markmaking allows us to alter how we convey the texture (in terms of how densely we pack in that information) without changing the nature of the texture itself, which we can see here on this example of bush viper scales.

Another point to consider however is that this can be pretty easily detected with very chunky textures, but when we're dealing with much shallower grooves, the distinction between doing it correctly and incorrectly can be pretty slight. Hell, the actual visual result can be the exact same, but the manner we think about it can make the difference.

In effect, when dealing with tires with shallow grooves - or any texture with holes in it - students can be prone to viewing the groove itself as being the "textural form" in question. So, they focus on drawing it, filling in the groove with black and moving on. But of course, the groove isn't a form - it's an absence of form. Instead, the forms in question are the walls along the sides of the groove, casting shadows upon one another, and upon the floor of the groove itself. This diagram demonstrates this concept visually, to make it somewhat easier to understand.

Lastly, I wanted to give you a couple additional diagrams - more focused on how we think through the texture analysis exercise in Lesson 2 - but still applicable here since it's all about understanding how to approach identifying our forms without drawing them, so we can imply them with cast shadows alone.

• Firstly, this diagram (or alternatively this one which is essentially the same, just framed a little differently in case it makes more sense) demonstrates how texture requires us to think about the relationship between the light source and each individual form.

• And secondly, this diagram shows, using a texture of melted wax, how we can think about first identifying the forms themselves, and then designing the shadows they'll cast.

Anyway! As I mentioned, the "trap" aspect of this challenge is very much by design - so I'll still be marking this challenge as complete. Just be sure to review the texture material, especially these notes.