As per your explanation, I won't touch on the fact that there's no degree shift in your wheels. I can however assure you that students are by no means required to splurge on a whole set of ellipse guides. You weren't actually that far off in picking up a single template sheet - most students pick up what is called a "master ellipse template". Basically it includes a variety of different degrees, but only in a few sizes, none of them particularly large. While the wheel challenge works out pretty well even if all the degrees are kept the same (it simply results in a lack of foreshortening, which at the same of these kinds of objects isn't such a big deal), you'll find that being able to use different degrees is advantageous in Lesson 7.

All that said, when it comes to construction, you're doing an excellent job. Your wheel constructions are solid, both in terms of how you're using multiple ellipses to capture the impression of an "inflated" wheel rather than a simple stiff tube (although number 3 did end up lacking this, and thus came out more rigid - not sure if that was intentional), as well as in your attention to the actual rims/spokes inside of each wheel. You've taken a great deal of care in distributing the different spokes to keep them evenly spaced out, and you've remained quite conscious of the fact that everything involved here is a solid, three dimensional form - down to respecting the need for every structure to have multiple planes in order to exist in three dimensions.

Now, while your construction here is superb, it appears to me that you may have forgotten some of the textural principles from Lesson 2, as you appear to have gone as far as to construct your tire treads as well, employing explicit markmaking techniques here when the implicit techniques explored in Lesson 2 would have been more suitable. This of course is largely expected - at this far end of the course, we're far enough removed from Lesson 2 that the majority of students forget about those concepts, and so I use this challenge to remind them of its existence.

This issue isn't really significant when dealing with the simpler tire treads that are composed largely of grooves (although there is something we'll discuss briefly on that topic in a moment) - it's those tires with larger "chunks" in their treads where the implicit markmaking techniques become considerably more useful. Either way, the main thing to keep in mind is this - right now we're just drawing wheels floating in a void, and so a really complex tire tread like number 7 can be visually dense and draw a lot of attention without issue. If you drop that wheel into another drawing however, we're quickly going to end up competing with the rest of the drawing, creating a focal point that draws the viewer's eye whether you want it to or not.

Explicit markmaking - that is, outlining each textural form - doesn't really give us a lot of control over how we choose to convey the presence of the forms we draw. Rather, that which exists in the world has to be drawn, there's no two ways about it. Implicit markmaking however, allows us with a fair bit more flexibility, specifically because by drawing the shadows those textural forms cast (instead of outlining each of them in their entirety), we actually end up separating that which is drawn from that which exists. To put it simply, it breaks the assumption in the viewer's mind that only the things we've actually drawn exist.

This isn't a tire tread, but this african bush viper scale study does a good job of conveying the concept all the same. Despite having entirely different marks, we still understand that the same forms are being conveyed. We can, if necessary, pull back and really minimize the presence of those shadows, and leave just enough information for the viewer's brain to fill in the gaps, effectively reducing how much attention it draws but not actually changing what is represented.

Now jumping back to those shallower groove-based tire treads, there is one thing to keep in mind here as well - and that is the fact that regardless of the nature of the texture, we have to always keep in mind that the marks we're putting down are not literal, direct representations of something physical on our object's surface. They are shadows - and therefore, they are being cast by the forms that make up the walls around the grooves. If you take a look at number 21, here you've drawn those grooves directly - you've drawn a line to represent every groove. This was not done with consideration of the physical forms, but rather, each line represents an absence of form, a negative space. As a result, it does not really feel like a surface with variation in three dimensions - instead, it feels more like someone's drawn a grid pattern onto a smooth, cylindrical surface.

Even though the difference can be almost imperceptibly subtle, it's important that as you draw these textures, you're always aware of what it is your marks are meant to represent. Focus on the forms that are present - your reference image serves as a source of information, from which you'll derive understanding of the textural forms, how they sit in space, and how they relate to their neighbours. It's that understanding which determines the marks we draw, rather than a direct transference of what we see in our reference right into our drawings.

So! Be sure to go back over the texture section from Lesson 2. You are of course free to consider this challenge complete - while you did fall into the expected trap, most do, and that will not hold you back from continuing on.