Despite the obvious restrictions you had working with your limited set of 30 degree ellipses, your wheel constructions here are still really quite well done. You've pinned down all the various ellipses required (more than just the ends of a cylinder) to provide a solid structure with the nuanced curves that actually make them feel like wheels. The ellipses themselves aren't perfect, on account of most of them being freehanded, but all the same you worked within those limitations to achieve fairly solid results all the same.

When it comes to your tire treads, there is an issue in how you approached some of them, but it only really comes into play when looking at tires with really chunky treads. For example, number 14. Here you've got strongly visible forms coming off the surface of the tire, and in order to capture them you constructed each one very explicitly. Because these forms sit on the surface of another object in this manner however, they're technically still something we can choose to treat as texture - and therefore we can use implicit drawing techniques to capture and convey this information to the viewer.

It is a choice, but the main reason we'd opt to focus entirely on implying the presence of these forms rather than constructing them explicitly is that explicit techniques require a lot of extra linework that can create unintentional focal points on our drawing. With all the extra lines, they can draw the viewer's eye in ways you may not have intended. Relying on implicit techniques allows us to work in bigger, but less visually demanding shadow shapes.

Here you definitely did draw the shadows those forms were casting, which is great - but it obviously was a little intimidating to draw those shadows without constructing each individual form. As you can see here, the internal edges aren't necessary. All you need to do is first focus on how the cast shadow defines part of the silhouette, then look at whether that form breaks the silhouette of the original form (the tire), and defining that portion as well. Do as much as you can with shadow shapes alone, then define whatever remaining outlines are necessary if you truly feel they are needed to communicate the forms to the viewer.

Construction is comforting - we build everything out so precisely that we can understand it as it exists, and so it helps give us all the information we need to then go on to put down cast shadows. So when we take that tool away in regards to texture, students definitely struggle a great deal. Don't worry though - as you focus on each individual form, you will be able to determine the appropriate shadows and how they should be drawn. It just demands a lot more focus, and perhaps a little more time.

When it comes to the tires with shallower grooves, I think these rules, while still present and relevant, aren't as important simply because we don't have to worry about all the extra explicit construction lines drawing the viewer's attention. For example, looking at wheel 22, you drew those forms and outlined the tread texture over the entire wheel, but because of the fact that the tread wasn't quite so deep or chunky, it didn't result in distracting focal points. At the end of the day, how you approach texture comes down to choice, and with experience you'll learn what you'll be able to get away with, and when leaning more heavily on textural techniques will be more necessary to achieve the results you want.

Anyway, all in all your work here is coming along well. I'll go ahead and mark this challenge as complete.