Nice work! To start, your constructions are definitely coming along fairly nicely, and you've put a good bit of effort into pinning down the various rims on the different wheels. Before I get into how you tackled the tire tread textures, I have a couple of suggestions to offer:

• It looks like for the majority of your wheels, you constructed what was essentially a cylinder with one clear ellipse on either end, then usually some smaller concentric ellipses along the side facing the viewer to help pin down the rims/hubcap. What can definitely help a fair bit is to include one or more ellipses through the midsection to help define the form a little more specifically, as wheels aren't quite a cylinder, but rather have a bit of a bulge through the middle. You do appear to be aware of this, but it looks like you establish the constructional marks to pin that down. Before we get into any detail/texture/etc, establishing the whole construction and everything it will require is important, so don't skip any steps.

• There were a couple places, like wheel 11, where you used a bit of hatching on the rims. Just in general it's best not to use any hatching within this course. Hatching isn't inherently bad or anything, but since we're not getting into any form shading/rendering, it doesn't serve any purpose and instead tends to cause students to focus too much on the idea that they're trying to decorate their drawing.

I mentioned this back in my critique of your lesson 4 work, but it's been a while so here's a quick reminder:

What we're doing in this course can be broken into two distinct sections - construction and texture - and they both focus on the same concept. With construction we're communicating to the viewer what they need to know to understand how they might manipulate this object with their hands, were it in front of them. With texture, we're communicating to the viewer what they need to know to understand what it'd feel like to run their fingers over the object's various surfaces. Both of these focus on communicating three dimensional information. Both sections have specific jobs to accomplish, and none of it has to do with making the drawing look nice.

Of course, I only saw this in a couple places, but it's important enough to make very clear all the same.

Moving onto your tire tread textures, I can definitely see that you tried to think a great deal about how to approach capturing these tire treads, and frankly just how much time and effort you put into figuring it out is what's most important. Overall you did show a great deal of progress, and you clearly focused more and more on specific cast shadow shapes above all else, so that's great. What you struggled with most was definitely transitioning from sparse to dense areas of texture, and the biggest cause for this is that your process does not entirely consist of focusing on cast shadow shapes.

For example, if we look at #16 on this page, you've got these 4 lines wrapping around the tire that come down from the top, stop, and then resume again towards the bottom. Because they're lines, and not shadow shapes, they actually remain fairly uniform and are unable to actually taper past a certain width, giving the impression that they stop suddenly. It's very similar to the issue that is demonstrated here when drawing cracks. On the left side, they're just lines, and due to the way we draw such lines (especially if they're drawn more slowly), they'll only taper so much.

The more confidently you draw such lines, the more they'll taper, as shown here, but when it comes to texture it really is best just to draw your shadow shapes using this two step process, focusing on really drawing everything as an enclosed shape rather than using individual strokes.

Another point to keep in mind is that when you've got big tire tread chunks, I'd avoid drawing their interior details. You tend to try and half-construct them, providing some of the edges to distinguish the form's planes (like in #21 and #17), but as you can see here you can imply a form with separate planes to it perfectly well by just defining its silhouette. Moreover, you don't have to define the whole silhouette. Just focus entirely on the cast shadow, and there will be enough information provided to the viewer to get it across. The biggest problem is that students are afraid to lean so hard on cast shadows, and so they'll often hedge and try to include some amount of explicit outline to fully construct their forms as a crutch.

This isn't actually related to tires at all, but seeing it in my little collection of demos did make me think that it might still be helpful. Here's a demo of a viper's scales drawn around a cylinder. Notice how nothing is an outline - even the little bits that define boundaries of some of the scales - are all shadow shapes, and so they're able to shrink or expand in response to how the light plays off it. In order to work this way, we do indeed sometimes have to make educated guesses based on what we know of the forms that are present, and how they relate to the light source. At this stage, however, I'm confident that your spatial reasoning skills have indeed reached a point where you can do that.

Anyway! I've rambled on a lot about this, but I am largely very pleased with your results. So, I'll go ahead and mark this challenge as complete.