Jumping right in with the structural aspect of the challenge, you've done a pretty fantastic job as far as building out the core structure of the wheel with your ellipse guide. I'm pleased to see that you've taken the time to lay out as many ellipses as you require to create the particular profile of each wheel - this (specifically having the wheels widen through the midsection and shrink towards the ends) is particularly important with those tires that appear more "bouncy", giving the impression that they'd rebound if dropped, rather than simply landing with a thunk.

There is one area where I do believe you are struggling a little, and that is dealing with matters of depth when it comes to the spokes of the rims. I've added some notes here, but the issue is essentially that in the few cases where you have rims that would have visible depth to them (where there should be edges receding into the depth of the wheel, or where the back edge of the spoke's side plane is/should be visible, I'm getting the impression that the resolution of that depth and what it means for where your edges should stop/where they should be defined isn't receiving as much attention as it should.

The issue basically has two parts:

• Firstly, make sure that you're considering the thickness of those rims - don't just focus on the outward facing surface, but also consider the side planes that give it solidity.

• Secondly, keep in mind that the back edge of the side plane connects to the inner tube of the rims further back in space - so it should not be connecting to the same edge as the more forward edge of that side plane.

Continuing onto the textural aspect of the challenge, this is an area in which the challenge serves as a bit of a trap. Being as far removed from Lesson 2's textural concepts - specifically those touching on the implicit markmaking we use to convey the presence of the textural forms without locking ourselves into drawing them all in full detail - it's pretty common for students to simply forget that those principles were introduced there. So, most students fall into the category of either forgetting about implicit markmaking altogether (and just constructing the textural forms, outlining them in their entirety as they would any other structure), or attempt to imply them without using cast shadows as discussed in Lesson 2, instead focusing more on trying to achieve the same kind of result but on a more superficial level focusing on the desired outcome.

With the first category of students, it puts them in a situation where they have to draw every single textural form, creating a lot of situations where there is a lot of detail focused on the tire. This can look quite impressive in isolation, with the wheel floating in a void, but when we draw them as, say, part of a larger vehicle in an illustration, it creates a very strong focal point that draws the viewer's eye, whether you want them to or not. This makes it more difficult to control how the viewer experiences a piece, which while not part of what we cover in this course, is a pretty big aspect of composition, and plays a major role in illustration in general.

You however fell into the second category, where you've clearly tried to avoid locking yourself in that way, but the focus is entirely on the result, rather than the process of how to get there. When we focus on the result without understanding the mechanics by which it is achieved, it leaves a lot more room for inconsistency, where a particular arrangement of forms may be depicted one way in one case, but differently in another. These inconsistencies are picked up on by the viewer on a subconscious level, and it can make things look "off". More immediately though, it can also give us a much harder time of controlling the results - you probably noticed that it was especially difficult to transition from one level of detail density to another, without feeling like it was "jumping" more arbitrarily.

The way in which we explore texture in Lesson 2 essentially comes back to the core principles of the course - it's all about spatial reasoning, and more specifically, understanding the relationships between the forms as they sit in 3D space. We focus on cast shadows both because the shape of the shadow itself and how it's designed conveys the relationship between the form casting the shadow and the surface receiving it, and because it allows for a much more straightforward way to transition from high detail density to low density without becoming inconsistent in the logic that drives it.

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. This means that on a single surface, you can ostensibly have the same textural forms being represented in different ways - those closer to the light source may cast no shadow at all, or at most very small ones (giving us low detail density, while those further away will steadily get larger and larger (increasing detail density to a point). Far enough away, the shadows get large enough that they start merging into one big complex shape (low detail density again).

Keeping the actual light source consistent and all that is less important than simply knowing that we can, on this basis, control where we want to include that greater density and leave our focal points, without being locked into them.

Of course, this is by no means easy - it requires us to consider both the nature of the form casting the shadow and the surface receiving it in mind in order to design the resulting cast shadow - but that's something that gets easier with practice, both in terms of direct practice of these textural concepts, and more generally as our spatial reasoning skills improve, allowing us to focus only on the relevant pieces (one textural form at a time) without being distracted by all else there is to consider about the texture as a whole.

There's one last thing I wanted to mention about this. 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.

Now! As I mentioned earlier, this is very much an intentional trap - it's not about cackling as students fall into it, it's about having an opportunity to share this information (or reiterate it) where it will have its greatest impact. In doing this, you've been shown an area of the course that you may have allowed to slip through the cracks a little, and so that's simply a reminder to consider other such areas that may exist, and going back to review them. I will still be marking this challenge as complete, but I recommend that you reflect on any areas of the course you may have neglected in your warmups, and review them before continuing on with the last lesson. A good place to start, as far as the textural concepts go, are these reminders.