Good stuff! Starting with your construction, your wheels are coming along great. Both in terms of the overall cylindrical structure, which features plenty of cross-sectional ellipses, establishing a gentle bump in profile to give that sense of an "inflated" tire, rather than something harder than it ought to be. Furthermore, when it comes to your rims, you're largely doing a great job of building up those structures both with consideration for the front face and the forms' side planes to ensure that they all feel tangible and three dimensional.

One small thing to note - remember that as we're focusing our filled areas of solid black with cast shadows, always be careful when you reach to fill in an existing shape with black - for example, the inner rim of 17. Cast shadow shapes would almost always be their own separate shape that needs to be designed - with that shape's design actually being what implies the presence of a specific form, be it structural or textural. If you find yourself in a situation where you need to fill an existing shape in, always think twice about what it is you're really doing.

Continuing onto your tire treads, I'm very pleased that you remembered the principles from Lesson 2. For most students, this challenge is a trap - one they step in when they fall back to all of the explicit markmaking, and basically forget that the texture section of Lesson 2 exists. The purpose of the challenge is to either ensure that the student remembers those concepts as you do, or that they realize they need to go back and refresh their memory.

By and large you're doing a good job in laying down those cast shadow shapes - I imagine you'd do even better if your wheels were bigger, but the limitations of a master ellipse template are what they are, and it's better in this case to stick with a smaller wheel using the ellipse guide, rather than freehanding a larger one.

That said, I can give some advice in terms of how to think about the tire treads with "grooves", like the diagonal treads you were mentioning. This isn't necessarily going to help you a ton when dealing in such a small space (what you did was really the best you could have), but there is something to be said about shallow grooves as a texture - and this goes for really any kind of texture with holes at all.

The issue is that we're prone to looking at the grooves and holes as though they're the texture - but they're not. In fact, the textural forms at play are in fact the walls and floors of those negative spaces, and so we need to keep in mind that we're not simply drawing those holes and grooves as lines. We're still capturing shadow shapes, designing them such that they imply the presence of the forms that cast them. For that, this diagram may help. It explains what light is actually doing when it enters such a negative space, and what exactly is casting the shadow.

Anyway, as a whole you've done a great job. I'll go ahead and mark this challenge as complete.