Very nice work! As a whole, your wheel constructions are very well done. You've shown a great deal of care in lining up your ellipses and laying out as many ellipses as were necessary to create some of the more complex structures, and achieving the appropriate beveling/curvature that some of these wheels require. You also paid a great deal of attention to the rims, constructing the various spokes so they each felt solidly three dimensional rather than just like stickers affixed to the cylinder's side.

When it comes to the tire treads, it's clear that you put a lot of work into drawing them carefully, but there is a key point that you appear to have forgotten. Way back in Lesson 2, where we talk about how we approach drawing texture, we discuss the topic of the difference between explicit drawing techniques and implicit drawing techniques. When approaching texture, we specifically employ implicit drawing techniques - which means implying the presence of textural forms by drawing the shadows they cast on their surroundings, rather than explicitly outlining each and every form.

The treads of tires are a texture. Even when they stick out a lot form the surface, they're still like a "skin" that wraps around the basic construction of the wheel, and as a result, we should be implying those textural forms by capturing the shadows they cast on their surroundings. Where they break the silhouette of the form, we can employ outlines, but all of the internal detail should be implied, rather than fully outlined as you've done here.

This is actually a somewhat common mistake students make at this stage, likely because it's so far from Lesson 2 that many of them have forgotten, and allowed it to slip. It serves as a good reminder that the techniques covered long ago are still important and valuable. These techniques can also make a challenge like this somewhat easier - instead of having to draw everything in such detail, we can remember that our purpose here is to communicate the textures to the viewer, not to simply decorate our drawing. It is often possible to communicate what it'd feel like to run your hands over the surface of a tire with far fewer marks, focusing only on a few key shadow shapes to imply the presence of certain forms.

So! Be sure to keep that in mind when moving forward, and I strongly recommend that you go back and reread the texture section from lesson 2, as it appears you've definitely forgotten some of its rules and principles. Don't worry though - the construction of your wheels is what I am most interested in here, and you've done an excellent job with it throughout. As such, I'll go ahead and mark this lesson as complete.