Nice work! despite having to freehand all your ellipses, you've largely done a pretty solid job with them, and managed to deal with the odd ellipse being a little uneven or out of place fairly well. As a result, your constructions are pretty solid, and you've demonstrated a lot of care in identifying how each one should be constructed (with several concentric ellipses), and approached your tire treads with a careful eye.

There is just one issue that I want to address, and it's a common one. It's related to how you tackle the tire treads with larger, more prominent forms - like the tires with chunkier grips, such as numbers 10 and 20. Basically it comes back to the texture principles from Lesson 2. That is, we want to capture textural forms not by drawing them directly, but by implying their presence by capturing the shadows they cast on their surroundings. We focus primarily on cast shadows, not on form shading - meaning that when suggesting that a certain form is present, we don't actually draw any marks that go directly on that form. They always go on the forms surrounding it.

So, if we look at wheel 20, you've got those big long chunks, and you've outlined them and filled in one of their faces with solid black. Basically you captured it through explicit means, using the ink for form shading rather than cast shadows. You can see the difference of approach in this simple diagram. As you can see there, you can still capture the fact that a form is three dimensional in the way that its silhouette is defined - you don't need to be quite so blatant in separating its top plane from its side in order to achieve that. Furthermore, drawing the cast shadow can also help you define the relationship between the given form and the surfaces around it, which allows us to convey more information than when we were using our black shapes as shown on the left side of the diagram.

So! Just keep that point in mind when tackling texture of any kind. Aside from that, your work here is good. I hope you'll be able to get your hands on some ellipse guides for lesson 7, as it will end up being quite useful not just in terms of drawing wheels, but also in other concepts we cover there.