No worries about the reference - while there are situations where in a critique of any lesson references for a particular drawing may be asked for, it's not that frequent, and is only to further help in the case of providing demonstrations. In the case of the wheels challenge, it's generally pretty easy to understand what the reference was like from the way in which the wheels are drawn.

Anyway, getting into the critique, we'll start with the structural aspect of the challenge. Here you've done quite well, both in how when constructing the overall body of the wheel/tire, you widened the midsection. This creates an arcing profile for the wheel, which helps to convey to the viewer that it would land with a bounce, rather than a heavy think, making it feel more "inflated" as opposed to solid and dense. Additionally, I'm glad to see that you've been mindful of both the outer faces of your rims/spokes as well as the side planes of those structures, although there is an issue I noticed with where the side planes of those spokes is allowed to end. Currently you're having both the edge of the side plane that is closer to the viewer, and the one that is farther from the viewer, cut off at the same edge. I've explained this on top of your work here. In essence, it comes down to the fact that you're allowing yourself to focus on the lines as they exist on the flat page, when you should always be thinking about the 3D forms they represent, and how they relate to one another in 3D space.

Continuing onto the textural aspect of the wheel challenge, this is an area that serves by and large as a trap. Being as far removed from Lesson 2 and its textural drawing concepts, especially those relating to implicit vs. explicit markmaking and the use of cast shadows to imply the presence of textural forms, rather than drawing them or constructing them directly, it's very common for students to simply forget all that stuff, and to neglect to continue practicing it regularly so it can properly take root. By highlighting that lapse here, we can make a fairly strong point for students to ensure that they reflect upon what other things they may have allowed to slip through the cracks, and to go back and review them on tehir own prior to moving forward with the final lesson of the course.

You certainly have fallen into this trap, although not as much as one could. You are still working with explicit markmaking rather than implicit markmaking, but I can see that you are clearly making an effort to work in filled areas of solid black, which suggests that you are still trying to apply the concepts from Lesson 2, though you are running into some issues with it.

Working with shapes of solid black is a step in the right direction, but we have to ensure we understand the distinction between a cast shadow - which is a new shape we introduce to our drawing, whose design conveys the relationship between the form casting the shadow, and the surface receiving it - and other uses of filled areas of solid black. A common other use is where we fill in the side planes of our textural forms. This is a very common "middle ground" (in the sense that students who struggle to wrap their heads around the admittedly challenging problem of figuring out how to design the completely new shape for a cast shadow), and so they find that drawing the textural form's individual planes then filling one in is a more "comfortable" way for them to continue using the filled areas of solid black.

Unfortunately however, it's altering the task to make it easier, and in so doing, turns it into a completely different thing. When we fill those side planes in, it's more akin to form shading. That is, where we're making a surface lighter or darker based on whether or not it faces towards or away from the light source. Normally this has the benefit of different midtones, but we're functionally still doing the same thing, just limited to solid black and white. As explained here, form shading is not something we want to include in our drawings for this course, so it's not what we want to be doing here. You should also be avoiding this when drawing the spokes of your rims, which we can see in cases like 10 and 15.

The reason filling in the side planes isn't the same is that it falls under the category of explicit markmaking. We draw the textural form in its entirety (defining all the separate planes with edges/outlines), then we apply the solid black. This forces us to draw every textural form in its entirety. Now, when we're dealing with wheels floating in isolation as we are here, that isn't an obvious problem - but when we do this as part of a larger illustration, that densely packed area of contrast and detail will create a focal point, drawing the viewer's eye to it regardless of whether you want it to or not.

Conversely, implicit markmaking is something we stress for textural detail for the simple reason that it is something over which we have far more control. Since we're drawing the shadows those forms cast, and not the forms casting them, we do not end up being forced to draw every textural form, and we have control over whether we want to increase the detail/contrast density, or keep it very low. We can do this by making the shadows larger or smaller.

If you recall the texture analysis exercise, it involves us laying textural forms across a flat surface and drawing them from a top-down view. If seen from the side however, it might look more like this. A series of individual forms arranged on the surface, with the light source to one side. Those textural forms closer to the light source end up being hit by the light rays at a much steeper angle, resulting in a very short shadow. Those farther away get hit at a much shallower angle, which then results in a much longer shadow. On this basis, this means that there's grounds for inconsistency in how the same texture might be conveyed in different places. That gives us more control, more room to decide that we want more detail density in one area, and less in another.

Still, we have to remember that what we're doing is not simply copying what we see from our reference image. As explained here in Lesson 2, we observe our reference in order to understand what kinds of textural forms are present, but it falls to us to understand how those forms relate to one another in space, and to use that understanding to design the shapes for the shadows that result.

Now this whole time I've made it out as though this is something you were largely unaware of, and that's not entirely fair. In fact, there are a number of places where you have made very clear attempts to work not with form shading, but with actual cast shadows. We can see this in cases like wheel 9 for certain, as well as perhaps in places like wheel 6, 18, and so forth. This kind of problem is one that is genuinely hard to wrap one's head around, and so you deserve credit for the steps forward you've made. I don't want you leaving this critique thinking that your efforts were fruitless - they weren't, you're just still working through this problem, and hopefully the explanations I've provided here have helped.

To that point, there's one last bit of information I want to share, and it has to do with the kind of textures that are made up of holes, grooves, cracks, etc - basically anything where the name of the texture refers not to an actual form, but rather an absence of form. As explained in this diagram, such cases often result in students simply drawing those grooves as lines, or drawing them as flat shapes on the surface of the wheel, then filling them in (which is basically the same, just resulting in thicker lines). This can give a correct result in certain cases, or at least a correct-enough result that can pass at a glance, but it's actually no different from a wheel that had a flat pattern painted on top of it consisting of a bunch of lines or shapes. Think of it like wallpaper, as opposed to texture.

Of course, everything we're doing in this course is an exercise, and so it's not about the end result being close enough - it's about the actual spatial problem we're thinking about as we do the exercise that matters, so it's still important that we push to think about the problems as 3D spatial ones, involving forms that relate to one another in space, and try to keep a look out for instances where we fall into simplified patterns of behaviour.

Anyway, you're no doubt worried at this point that you're gonna be slapped with a lot of revisions, but that is not the case. This is a fairly normal and expected outcome for the challenge, and as I explained previously, its purpose is to be a bit of a reminder that maybe one's understanding of texture has holes in it, and that there may be other things that perhaps should have been practiced more as warmups.

So! I'll mark this challenge as complete, and will leave you to review whatever you feel needs it.