Nice work! While some of your ellipses do get noticeably off-kilter (I assume this is largely when you end up having to freehand an intermediary ellipse), all in all your results have come out pretty well. The wheels along the first page were admittedly pretty similar - like a repetition of the same wheel, in the same orientation, but I'm glad to see that as you got comfortable with that one wheel, that you did start pushing into greater variety both in how they're oriented in space, and in general design.

There's really only one issue I want to touch upon, and that has to do with how you tackle some of the chunkier tire treads. Remember that tire tread is itself a texture, a series of forms that adhere to the surface of a larger form. As such, in order to capture them we'd want to use the implicit drawing techniques covered back in Lesson 2's texture section.

The key is that in outlining your chunks of tread, you employed constructional, explicit drawing techniques. You drew each chunk, defining it in its entirety, instead of implying the presence of those textural forms by capturing the shadows they'd cast on their surroundings. This generally results in a much noisier texture that can be more difficult to parse visually due to all of the individual lines present there. Using shadow shapes instead allows some of those marks to merge into one another where needed, diminishing the density of contrast and allowing us to keep this kind of detail from getting distracting.

Looking at 16 in particular, you did try to use larger filled black shapes, but you did so to fill the side planes of those chunks. As shown here, always reserve those filled shapes for cast shadows only. You can see there that leaving no internal edges within the silhouette of the textural form doesn't make it any harder to understand how it exists in 3D space. At the same time, the cast shadow helps define the relationship in space between the textural form and the surface to which it adheres.

One last thing - a trick that can help you avoid the trap of using outlines and lines in your textures, is to purposely break your mark-making into a two-step process, as shown here. By first outlining a closed shape, then filling it in, you guarantee that you won't accidentally be outlining your textural forms needlessly. Now obviously there are exceptions - for example, if the textural form breaks the silhouette of the original object, then you'd still be using an outline to show how it breaks that silhouette. But for any internal marks, focusing on shadow shapes only will help keep you in line.

So! I'll go ahead and mark this challenge as complete.