Your ellipse guide issues are quite normal - ultimately most students have to settle for those more limited ellipse guides (although there are ones with a bit more degree variety, up to around 5 degrees). I will say however that we're already hard at work trying to provide an alternative. I've purchased a laser cutter (no small investment, at $4000!) for Jordan, who handles our pen sales, and he has acquired a source of acrylic so we can figure out how to provide our own full ellipse guide sets for far cheaper than the usual $100+ (something closer to $30 or less).

Anyway, starting with the structural aspect of your constructions here, you're knocking it out of the park. I'm glad to see a nice subtle 'bump' through the midsection, which helps to establish the impression that the tire is inflated, rather than solid all the way through. You're also mindful of establishing the side planes of your rims' spokes, even despite the fairly limited space in which you're working. This helps to make them feel more tangible and real, rather than just flat and paper-thin.

When it comes to the tire treads, this challenge is something of a trap. It's very normal for students to, being so far removed at this point from Lesson 2, forget about the principles of implicit markmaking. As a result, it's common for them to end up with a lot of explicit markmaking. While this may seem okay given that our wheels are floating in the void, when we end up using them in actual vehicles, that densely packed collection of lines becomes very eye-catching, whether we want it to or not. This is better controlled through implicit markmaking, which, to your credit, you did end up playing with more on the last page of wheels, though to varying degrees.

You've got a few different things going on in this regard, and I'll talk about each one in turn. Starting with this one, the strip down the middle is coming along pretty well (though the outer sides are definitely more in the realm of explicit markmaking). I can see that you're thinking about the specific textural forms that are present, although I'm unsure of whether your intent is to draw the shadows being cast by the textural forms, or to fill in their side planes (the distinction between which can actually be very subtle, as shown here in this demonstration on another student's work.

While this one does use some clearly defined filled black shapes, it seems to me that your intent here is more clearly to fill the side plane, which would be incorrect. Our filled black shapes should always be reserved for cast shadows, whereas filling the side plane is more akin to capturing form shading (where the orientation of the surface determines whether it's dark or light). A cast shadow itself is a distinct shape of its own, where the design of that shape conveys the relationship between the form casting it and the surface receiving it. What you've done here still falls into the realm of explicit markmaking.

Lastly, with this one you end up relying more on random little marks. As explained in these notes from Lesson 2, texture is about identifying and understanding specific forms, and then using our understanding of how they sit in 3D space, and how they relate to the surfaces around them, to decide how to design the shadows they ought to cast.

So! I do recommend that you review those notes from Lesson 2, although I would not hold anyone back over a trap that I somewhat intentionally set. So, I'll go ahead and mark this challenge as complete.