Jumping right in with the structural aspect of the challenge, there's much you've done pretty well, although there are a number of points I want to draw to your attention:

• I noticed a number of cases where your ellipses were not aligned to your desired minor axis line - for example, number 15 and 16, we can see here that their actual alignments are off by a great deal.

• As shown here, sometimes when constructing the side planes of your wheels' spokes, you'd end up running all of your edges right up to the ellipse. The side plane however runs into this internal structure further down along its length than the front-face of the spokes, so one of those edges needs to stop sooner, where it would intersect with the 3D structure of the rim.

• Be mindful that all 3D structures are going to have some thickness to them (short of being paper-thin), and so ther are areas in some of your wheels where the thickness of certain forms was neglected, as shown here.

Carrying onto the textural aspect of the challenge, we often do find that being as far removed from Lesson 2 as we are, many students have a tendency to forget that texture is to be approached in a specific fashion, employing things like the implicit markmaking discussed there (where the marks we actually draw are the shadows the specific textural forms cast upon the surfaces around them), and so this challenge serves as a sort of "trap" to catch such situations. It does appear that you've very much fallen into that trap, as it does not seem you really attempted to apply any of the textural concepts to how you captured the tire tread textures here.

So firstly, let's briefly talk about why implicit markmaking would be beneficial here. Firstly, the tire tread falls into our definition of texture, which requires a series of forms to be arranged along the surface of another object. In this case we have the simple cylindrical wheel, and the various protruding forms or cuts along its surface being the texture. There are a lot of cases where, given that these wheels are drawn floating in the void, working with explicit markmaking seems to work okay. But, if we transplant the wheels into a larger vehicle construction, we'll quickly find that the cases where the more complex textural arrangements with more textural forms (like 23) create very dense areas of details that turn into focal points, drawing the viewer's eye to them whether you want them to or not. As shown with this example of an african bush viper's scales, working with implicit markmaking allows us to change the density of visual detail without changing the actual information that detail is conveying to the viewer.

An important point to call out is that right now it appears that you're approaching these tire tread textures in a purely observational fashion - meaning, you seem to be focusing on what you see in your reference and transferring it directly onto the page as linework, though without considering what exactly those elements visible in the reference are actually telling you about the forms that are present upon that surface. As explained here, that intermediary "understanding" stage is critical, as it helps us determine the nature of the shadow we must design in order to convey the relationship between the form casting it, and the surface receiving it.

Furthermore, when it comes to textures with holes or grooves, there is a pitfall where one might consider the things to which we ascribe actual names - a groove, a hole, etc - as being the actual textural forms they're meant to be thinking about and understanding. This is not the case (given that the holes/grooves are the absence of form, with the walls surrounding them being the forms that cast shadows upon each other, and upon the floor of the holes themselves), but it does lead students to simply representing those grooves as lines, or filling in the holes with black, effectively taking that negative space and representing it entirely in black. This diagram helps to break down why this is not correct, and how to think about it instead.

Now, I will still be marking this challenge as complete. Given that it's a trap, it's not at all abnormal for students to fall into it - but it does mean that you will want to review the texture material from Lesson 2 prior to moving forward and completing the rest of the course, as right now it seems to very much be something you forgot existed.