Starting with the structural aspect of the challenge, your work here is coming along well. You've made good use of your ellipse guides to build out the body of your wheels, and I'm glad to see that you've varied just how much wider that midsection gets to properly convey the sense that the tire is inflated, and would land with a bounce rather than a heavy thud, as required by your various wheels.

While I am pleased to see that you have not just focused on the outer face of your wheels' spokes/rims, I did notice cases like number six where, as shown here the far edge of the side plane seems to extend out too far (as marked in blue). Since that back edge touches the inner rim further back, it would stop sooner, as shown in red.

Continuing onto the textural aspect of the challenge, this is a section where the challenge is something more of an intentional trap. Being as far removed from Lesson 2's principles on texture and implicit markmaking, it's very common for students to simply forget about those concepts, or to not quite remember them as well. The students who actually go back and review that material are in the minority, with many just approaching the details in whatever way they please, while others try to remember how to approach it per the instructions, but without necessarily going back and reviewing that material. I suspect that you fall into this latter group - your work suggests that you're mindful of the importance of relying on filled areas of solid black, but where our approach to texture focuses heavily on cast shadows, you appear to end up filling in the side planes of forms in most cases, which is more akin to form shading (which in turn as discussed here is something we actually avoid in this course).

It's not that the approach is generally wrong - all of the restrictions we face in this course apply to the course work only. Rather, we focus on cast shadows here because it comes back to the central focus always being on spatial reasoning. Where a form shadow involves a surface getting lighter or darker based on that surface facing towards or away from some light source, cast shadows actually define the relationship, through the design of their shape, between the form casting the shadow and the surface receiving it. That's why the design of the shadow shape, as discussed in these reminders is so important to us for this concept. If you're filling in shapes with black but never had to actually think about how to design that shape - if the shape was already there, it's a good idea to stop and ask yourself whether what you're drawing is actually a cast shadow.

Another reason we focus so much on cast shadows is because of the control it gives us in terms of how densely packed our details get. With wheels floating in a void like this, we can load up a wheel with tons of explicit detail and it may well look lovely as a result - but try and include that wheel in a larger illustration, and the wheel is going to draw a ton of attention due to the visual contrast of all those concentrated areas of light and dark.

Cast shadows are different. 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, even if you don't specifically worry about where the light source is, we know there's a logical reason that a texture can be represented with more detail density, or less detail density, without changing the nature of that texture. That's key - with explicit markmaking, you can always reduce the number of marks you're using, but that's simply going to tell the viewer that there are fewer forms present. This way of thinking in terms of cast shadows grants us far more control over how the viewer engages with what we're drawing, which leads into composition - which while outside of the scope of this course, is an important concept to learn.

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! Of course since the whole texture part is a trap, I don't assign revisions based on that. Instead, just be sure to review the material relating to texture, and also consider whether there are any other concepts from the course that you may have allowed to slip through the cracks, and be sure to review them as well before continuing on.