When critiquing this challenge in particular, I like to split it into two parts. First we look at construction, and then we look at texture (where you'll find I've left a little trap).

Starting with your construction, overall you're doing fairly decently. I think you're working with an ellipse guide, which is good to see - sometimes students try to work without, and while at this stage students have had a fair bit of practice with ellipses, the sheer level of precision the wheels require can cause the inaccuracies of freehand to really become a distraction from the core of this challenge. So, the core construction of your wheels is generally pretty good (there are a couple that get a little wonky - 18 for instance has a far end that seems to be narrower than the end closer to the viewer, and 11 seems to be very sketchy for some reason), but the majority of these lay out a solid structure, not only sticking to a basic cylinder but including that subtle bulge through the center, or beveling at the ends, to really give an "inflated" impression.

When it comes to the rims, I do think you probably could have taken more time, and that you did cut corners with some of them. 13 for instance was solid - you drew out each spoke, considered the way in which they exist in 3D space, with proper distinction between side and front planes. 9 and 10 however get very sloppy, where the complexity of the task is definitely demanding more time from you than you're willing to give it. Remember - we do not determine how long a drawing should take, certainly not by how much time we have to offer it in a given sitting. It's the complexity of the drawing that determines these things, and if we don't finish in one sitting, it's simply a matter of spreading it across several.

So, to put it simply - don't rush. The temptation to do so floats continuously around us, and it seeps in even without us noticing. We have to constantly be vigilant, auditing our motivations, and considering our actions. If you look at 25, there's definitely a lot of sloppiness in the rims there as well. Obviously we can see what you were going for, and all the pieces are there, they were just put down a little haphazardly, as does appear to be a trend here.

Now, continuing on, there are a few key reasons I included this challenge here. One is that wheels serve as a good representation of the challenges we encounter when drawing cars, but at a smaller scale. Each wheel has its own character, and they're all the product of someone taking the time to purposefully design them in such a way. This is also a great way to get accustomed to the use of ellipse guides, whose usefulness is expanded upon somewhat in Lesson 7.

A big reason for this challenge, however, is the aforementioned trap. Students at this stage are often so far removed from Lesson 2 that many of them tend to forget the principles relating to texture. They forget about the distinction between explicit and implicit markmaking, about the importance of relying on shadow shapes to imply the presence of their textural forms, and so on. This challenge serves as a reminder that these textural concepts exist, and it does so through the tires' treads.

Texture is essentially a series of forms that are arranged along the surface of another form. In this case, the wheel structure is the form, and the protruding chunks as well as the grooves cut into the surfaces of our tires are the texture. These are all things that exist in 3D space, but being as densely packed as they are, standard constructional approaches (which mostly revolve around explicit markmaking - outlining the forms in question) doesn't work so well, due to all of the visual noise it produces.

Needless to say, you've certainly fallen in to the trap. There's no shame in that - you're not the first, and you won't be the last. All it means is that you definitely will want to review the material from Lesson 2's texture section.

This issue becomes more apparent when we deal with tires that have larger "chunks" in their treads. 4, 7, 8, 14, 24 and 25 are all particularly good examples. Across these, in some you've drawn the tread chunks with some consideration to them as 3D forms, drawing not only their top planes, but also including their side planes as well. You do this in 14, 8, and a few others with varying success. Admittedly, working in such a small space (which is unavoidable due to the ellipse guide) definitely makes this harder, since you're trying to work with so many different little lines - but of course, we're not supposed to be working in this manner.

There are others where you get a little sloppier - for example, in 25, you basically just draw the top planes of these textures. They're also laid out with less planning and precision than some of the others, though I imagine you were probably hitting that point where you were pretty tired of the challenge altogether. A good time to take a break and revisit the work when you're fresh.

I'm not going to get into the correct way to capture these tire treads - it's really just a matter of figuring out what kinds of specific shadow shapes they ought to cast (once you understand how each textural form sits in space relative to its surroundings, designing the shadow it casts upon those surroundings is really just a matter of thinking on that specific spatial relationship between them). I will however touch upon why these methodologies are so important.

Ultimately, working with implicit markmaking is critical because of how it allows us to control both which marks we end up putting down, as well as what exactly they convey to the viewer. Explicit markmaking is straightforward. That which is drawn, exists. That which has not been drawn, doesn't exist. And so you end up having to outline a ton of textural forms, making a really noisy result. This may be fine if we're looking at wheels floating in the void, but as soon as you add these to an actual vehicle, all of that contrast is going to make the wheels a focal point, drawing the viewer's eye to them whether you want it to or not.

If however we were able to convey that tire tread texture to the viewer without so many marks, we'd be able to get across the right information, but without losing control of our focal points (which are extremely useful compositional tools, which fall way outside of this course but you can read about it in this old PDF of a drawabox composition that existed once upon a time). That of course is where these implicit techniques come in.

While this is a demonstration of a bush viper's scales and not a tire tread, it still gets the same principle across. You can work with more marks, or fewer marks, and still get the same texture across. By working implicitly and focusing on the shadows these textural forms cast, rather than on drawing the forms themselves, you can control how much visual noise and contrast you wish to include in a specific area.

Anyway, having said all that, you are still good to move onto the next lesson. Just keep in mind that Lesson 7 is a doozy. I've regularly had students spend 4 or 5 hours on each drawing, with some students going well over 10 hours when working on cars. Where you definitely hit an upper limit on some of these wheels, in terms of at which point you ended up getting kind of sloppy, it'll be important that when you tackle lesson 7, you expect to break each drawing up across multiple days. Always remember - your single responsibility as a student of this course is to give each and every drawing as much time as it requires.