Despite your struggles as you worked through this challenge, your results have largely come out quite well, and you've demonstrated a successful use of these new tools. Your wheel constructions feature solid base structures that go beyond the basic cylindrical structure, properly capturing that slight swelling towards the midsection of the form. You've also handled the rims/hub cap designs very well.

There is actually just one issue that I want to bring to your attention, and that is with a specific kind of tire tread where the tread itself gets much larger and chunkier. We can see this in cases such as #4, #13, #21 and #24. These are situations where the you've approached drawing the tire tread's textural forms using explicit drawing techniques. You may have forgotten some of the concepts from Lesson 2, in which case you can find an explanation of implicit vs. explicit drawing techniques here. The short of it is that you attempted to build out those "chunky" tire treads using construction, outlining those forms and drawing them directly, instead of treating them like a texture.

Since this is in fact a texture, we should still be implying the presence of those textural forms, not drawing them directly but rather suggesting that they're there by capturing the shadows they cast. You can see an example of this in this diagram, where on the right side you can see how the interior of the form itself has been left completely empty with no internal detail or edges. All of our effort is put on drawing the shadows being cast by this form.

Cast shadows are exceptionally useful because we can use them to convey the relationship between a form and the surfaces around it. If the form is tall, then it will cast a longer shadow. If it is smaller however, it'll cast a more minimal shadow. At the same time, the silhouette of the textural form itself is enough to still capture the fact that it's a three dimensional form - in the diagram I linked, you can still understand that you're looking at a box, even without the internal edges being pointed out to you explicitly.

This is an important point to keep in mind when dealing with any kind of texture that gets very large. Even though it's big and may seem like they're forms that should be drawn using constructional techniques, they're still adhering to this other form's surface and therefore behave like a texture. Applying construction to so many little forms can result in a lot more linework, which can make the drawing feel more noisy and distracting, and draw attention towards it unintentionally. Textural techniques are designed to convey information without being distracting in this manner.

One last thing - I noticed that on #24 you had a lot of random hatching lines throughout that very clearly weren't drawn with much thought. I'm not sure what they were there for, but try to avoid putting marks down without specifically thinking about what their purpose and task is, and then compare them back to what you've learned throughout this course to decide whether or not you should actually include them in your drawing.

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