Starting with the structural aspect of your wheels, by and large they're coming along quite well. I did notice that your linework did suffer a little when you got into some of the smaller structural elements (mainly the spokes - your lines were less intentional and purposeful, and tended to be more doubled up/sketchy. This often happens when we feel less confident, but remember - it's always a choice to be more intentional with your linework. It often feels when we're uncertain that it stops being an option, but that's just our brains trying to slip back into old patterns. Always reinforce your control over the choices you make, whenever you catch yourself slipping.

One point I do want you to avoid in the future (mind you this only applies to the work you do within this course, and is not a general rule), is to remember that as discussed here in Lesson 2, we don't want to engage in form shading - so where you tend to fill the side planes of your rims' spokes with solid black, note that this should be avoided. We generally want to save our filled areas of solid black for cast shadows only, as these shadow shapes actually serve a function that loops back into the main focus of the course: they define the relationship between the form casting the shadow, and the surface receiving it, and so they help define the kind of spatial relationships the course is designed to help us understand on a more instinctual level.

Continuing onto the textural aspect of the challenge, this part of the challenge is admittedly something of a trap. Being as far removed from Lesson 2 as we are, it's pretty common for students to have largely forgotten about the implicit markmaking techniques and other textural concepts we discussed there, and so when they jump into this challenge, they tend to fall into one of two camps:

• Either they approach the tire tread textures using a methodology that focuses on explicit markmaking (outlining everything, or otherwise trying to construct each textural form as we would any other structures)

• Or, they attempt to apply implicit markmaking techniques but without actually reviewing the material explaining them, and so they end up working explicitly while still using filled black shapes - so for example, using them in a manner more similar to form shading.

For the most part, you fall into the first category, and while your wheels do individually look very interesting and well detailed in isolation, as they float in the void, the level of detail density this inherently demands of you reveals its own issues should we ever attempt to draw tires this way in a larger illustration. Whether we intend it to or not, it would create very strong focal points, drawing the viewers' eyes to them, and limiting your ability to control how the viewer experiences a piece (which is a big part of composition).

The core problem here is that explicit markmaking locks us into a certain level of detail density, and doesn't make it possible to smoothly transition to less or more density as required - at least, not without giving the impression that the texture itself, and the forms that make it up, are no longer present. We're locked into an agreement with the viewer that if I draw something, it's there, and if I don't draw it, it's not there. With texture though, we want to be able to imply that forms are present even where we haven't drawn them fully, or even at all. Where explicit markmaking fails to give us this, implicit markmaking's use of cast shadows does.

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 that is cast being projected farther. This means that if we are only using the shadows forms cast to imply their presence - not outlining or constructing them in any other capacity - we don't have to stick to one size of shadow throughout the whole texture. The laws of reality afford us this tool that can provide enough information for the viewer to understand that a textural form is present, while also being able to manifest as larger, or smaller, in different locations along that surface.

It's not even a case where we have to worry about where exactly our light source is, and keep everything hyper-consistent - just the fact that we know a shadow cast by the same form can, in different places, be of different sizes, gives us all we need to be able to control where we want to include more detail density, and where we want to include less. Those objects farther from the light source will cast really big shadows that merge into one another - giving us a low level of detail density. Those objects closer to the light source will cast virtually no shadow at all, or at most very small ones, again giving us a low level of detail density. And in between those extremes, we have where the shadows are big enough to be visible for most of the individual forms, but small enough that they're not merging into a single complex mass. And, because of the control implicit markmaking affords us, we can transition between those different points as we please (which is what the texture analysis exercise from Lesson 2 focuses on).

The last thing I wanted to mention is that 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.

Anyway, as promised - it was an intentional trap, meant to give students a bit of a stronger reminder that there are likely things covered in the course that may have been allowed to slip through the cracks. So, be sure to reflect on what else there might be, and go back and review the lesson material relating to it. I will however go ahead and mark this challenge as complete.