Nicely done! To start, your construction is largely coming along very nicely, and I'm very pleased to see that you've picked up an ellipse guide to help you keep focused on the core purpose of this exercise. You've done a great job of laying out your cylinder forms, adding a little more complexity here and there to allow for the slight bulges and such through the midsection, and generally building up more nuance to their silhouettes.

Looking at the tire tread textures, I did notice that you generally opted to outline those tread forms in a lot of cases, but that there were quite a few where you tried to navigate how to approach them using the textural principles from lesson 2. There are definitely a few ways in which we can improve on this.

The first overall issue I want to call out is just that there were definitely places where you drifted into the territory of shading your overall wheel in a few cases, like 14, 15, etc. As discussed back in lesson 2, we definitely want to avoid shading for shading's own sake throughout this course, though arguably in 15 you were trying to use it to incorporate area where texture would help as a transition from light to dark. Unfortunately it didn't pan out too well.

One mistake I saw you making a fair bit was that instead of focusing on capturing the shadows each textural form would cast on its surroundings, you often instead filled in the side plane of a protruding form with solid black. That is, instead of actually casting a shadow onto the surrounding surface, you ended up trying to distinguish the different planes of the same form, making one black, and the other white. The difference is essentially what is shown in this diagram. The left example actually flattens out the form itself by turning it into a series of flat planes. The example on the right however actually still conveys the impression that the form within the silhouette is three dimensional (due to how the silhouette has corners, implying those different planes), and then also goes onto establish the relationship between the form and the surrounding surfaces using the cast shadow.

I see this quite prominently in 13, as well as 20/21.

Looking at 23 and 24, the way you drew the little X's across the tire tread is something you'd want to avoid, if you're really focusing on applying the textural techniques. Reason being, if you try and simplify a texture into a pattern, it's going to ignore the nuance of how every textural form interacts with its surroundings. We end up breaking the texture into positive and negative space, focusing more on how the gaps between forms exists, rather than establishing and thinking about each individual form, one by one. This situation becomes much harder to shift from dense to sparse (since there's either a line, or there's no line - there's no middle ground), and generally lacks the dynamism.

Now, I want to share with you this demonstration I did a while back. It's not of a tire - it's actually of a viper's scales, but I've found it to be quite useful in showing how we should think about these textural forms. While it'd be all too easy to just criss-cross a bunch of lines over its surface to end up with a lot of X's, that wouldn't accurately capture the texture we're after. Instead, we have to think about each textural form separately, and cast its shadows on those around it. We also need to consider this in conjunction with how the light is hitting a particular part of the form, to determine whether we want to make those shadow shapes small and subtle, or vast and deep. This can be changed as we move around if we like - we have full control over it.

Anyway, all in all your work here is still looking great, and structurally you've built out your forms very nicely. I'll go ahead and mark this challenge as complete.