So about starting with ballpoint and then moving onto fineliner, that isn't explicitly something you're not allowed to do in the instructions for this challenge in particular, but it is something I push students not to do both in Lesson 6's tools section and in Lesson 7's. In general, the whole concept of sketching with an underdrawing, then committing to your lines later on, is very much against the core spirit of this course, and is something that we do address elsewhere - like here in Lesson 2's form intersections. So just keep that in mind going forwards.

Anyway, that said you've done a pretty great job here. Starting with your construction, your use of the ellipse guide came along really well, and in general I'm very pleased to see the way in which you've leveraged multiple ellipses to flesh out the complex profiles of these wheels. Rather than sticking to a simple cylinder (except when appropriate, like 16), you worked in middle-sections that get a little bigger, which helps to convey a greater sense of inflation - that is, something that is actually filled with air, and has some structural give to it to absorb impact.

I'm also pleased with how you laid out your spokes and constructed your rims, with a lot of attention to how those elements exist as forms in 3D space, not merely drawing their front faces as paper-thin elements, but also factoring in the side faces that give them the thickness they require. Laying out spokes can indeed be challenging, and there were a couple hiccups (like the lower right quadrant on number 4) but this is by no means a mistake I hold against you. Rather, I'm very pleased with your overall success in identifying how to best spread them out.

When it comes to the second part of this challenge - texture, and how we tackle the tire treads themselves, this challenge is meant to be something of a trap for students. Given how far removed we are from Lesson 2, and its specific principles on texture and implicit markmaking, it's very normal for students to hit this stage having forgotten about them, and not having reviewed them recently enough. So, we end up seeing a lot more circumstances like 21 and 22, where students fall back to conveying their 'chunkier' tire treads with explicit marks. That is, outlines, as well as filling in the side planes of the textural forms, rather than working implicitly which would involve only the use of cast shadow shapes (without excessive outlining).

Tire treads are, after all, just a series of forms running along the basic cylindrical structure of the wheel, and thus they very much align with the properties that make them suitable for textural markmaking methods.

Now I didn't actually see you falling into the trap of filling in your textural forms' side planes all that much, but I still felt it would be worthwhile to share this quick diagram I made for another student who was running into the problem quite a bit more. In the top, we've got the structural outlines for the given form - of course, since we want to work implicitly, we cannot use outlines. In the second row, we've got two options for conveying that textural form through the use of filled black shapes. On the left, they fill in the side planes, placing those shapes on the surface of the form itself, and actually filling in areas that are already enclosed and defined on the form and leaving its "top" face empty. This would be incorrect, more similar to form shading and not a cast shadow. On the right, we have an actual cast shadow - they look similar, but the key point to pay attention to is shown in the third row - it is the actual silhouette of the form itself which is implied. We've removed all of the internal edges of the form, and so while it looks kind of like the top face, but if you look more closely, it has certain subtle elements that are much more nuanced - instead of just using purely horizontal and vertical edges, we have some diagonals that come from the edges of the textural form that exist in the "depth" dimension of space (so if your horizontals were X and your verticals were Y, those diagonals come from that which exists in the Z dimension).

This is all beneficial because working implicitly like this separates that which is being conveyed (the textural forms themselves) and the marks that are being used to convey them. Where explicit markmaking, with all of its outlines requires you to draw every single one of those tread chunks, working implicitly does not, and actually focuses on giving the viewer's brain as much information as it needs to fill in the rest itself. You can see this demonstrated in this example - which, while being of a bush viper's scales, it's actually still quite similar to the problem we're dealing with here. We can choose to convey the texture with more ink, or with less, and we choose which one's most appropriate based on our needs.

If however we're locked into drawing every single outline, then that may work fine when we're looking at wheels floating in the void, but as soon as we slap them onto a car, we're going to end up with a focal area that draws the viewer's eye, whether you want it to or not.

Anyway! As I said, you fell into a trap, and I fully expect the majority of students to do so. That doesn't mean you require any revisions, or any such thing - rather, it was just a good opportunity to present a bit of a reminder. All in all you've still done a great job, so I'll go ahead and mark this challenge as complete.