Starting with your wheel constructions, overall you've done a pretty good job here, though there were a couple things that I wanted to call out.

Firstly - and this doesn't really matter because it was right at the beginning of the set - I wanted to just quickly call out that on number 1, you had the degree shift for your ellipses backwards, opting to use the wider one as the end facing the viewer. It definitely should have been the narrower ellipse on the right side that was facing the viewer. Fortunately, this is something that you ultimately came to understand on your own.

Now, I can see that in a number of these you definitely were happy to employ lots of ellipses to build out more complex wheel structures. In this regard, 21 stands out quite well. I do however feel that there were some places where a few more ellipses, especially to smooth out the ends of tires to achieve that "inflated" look rather than relying on a more straightforward cylinder would have helped a great deal. Just going for a simple cylinder and slapping texture on top of that will result in an amount of stiffness that won't quite capture the sense that we're looking at a structure full of air, that can absorb a decent impact. Instead it looks more solid and fragile. Another point that does help with this is to ensure that the central ellipse is larger (so the wheel's physical diameter gets bigger through the midsection), which I can see you employing in a number of these already, so that's good. Just be sure to bevel the sides a little more as well, and you should be good.

Moving onto the matter of the tire tread textures, I am glad to see that you thought back to the concepts from Lesson 2, and tried to apply them here. As far as the hatching lines go, to convey the curved nature of a form, you are right in both regards. That is, it is a useful technique that we employ here and there to convey curvature, but it also does quickly fall into the territory of form shading. For this reason, I try to minimize where it's used, and I think quite hard on whether or not it's really necessary before adding it. So, you are allowed to employ it, just make sure it's for a good reason when you do so.

One thing that did stand out in terms of how you were approaching conveying these textures was that while you were clearly trying to strategically place marks to limit their density to specific areas, I did still get the impression that the marks you were drawing were tied more to the impression you wanted to produce, rather than thinking about specific textural forms that were present on the surface of your objects. That is ultimately what makes texture so challenging - the textural marks we put down (generally as individual cast shadow shapes, where we outline a given shape first, then fill it in) are meant to directly imply the presence of a specific form. In the case of chunkier tire treads, that means that each specific shadow shape we design needs to relate directly to a form that is present, with one key challenge - we can't draw the textural form in the first place. We have to hold our understanding of where it occupies space and how it relates to the surfaces around it in our mind. That's a lot to ask of our spatial reasoning skills.

You do have solid progress in this regard in a number of places - like I can see you thinking about this stuff quite clearly in wheel 22. Just keep pushing yourself to ensure those cast shadow shapes are designed as intentionally as possible. One example I sometimes share with students at this stage isn't actually a tire texture. Rather, these african bush viper scales can help illustrate how every individual cast shadow shape serves to imply specific information about how a given scale sits in the world. If we choose to deepen the shadows and allow them to merge together, the individual shapes still matter a lot, because they ultimately determine the specific outline of the larger amalgamated shadow shape they combine to produce.

So! All in all your work throughout this challenge is coming along well, and I'm glad to see that you didn't forget about lesson 2's texture section, as many students do. It's definitely true that number 25 went way beyond what was asked for this challenge (being that it's not actually a wheel - you could have focused instead on a driving gear or something) - but I'll let that one slide.

You may consider this challenge complete.