I can see that you initially tried to freehand your first one - and then quickly came to your senses and went with your teeny-tiny ellipse guide for the rest. Doing so was very much the right call, so congratulations on that front. I can definitely see why you were uncertain at first, given just how small the other wheels are, but ultimately they are far better - and you definitely benefited far more from the exercise - for having use the ellipse guide, eliminating unnecessary complication from the equation.

Starting with your constructions, you've generally handled this quite well, although I am noticing a tendency to work somewhat more with straight cylinders - that is, ones that maintain an equal width throughout their lengths, focusing the tapering with additional ellipses towards the ends instead. This may be appropriate for some wheels, but it does generally give an impression of stiffness, rather than the "give" we would generally see from a more inflated tire. This is something we can achieve, when it's needed, by incorporating a larger ellipse in the middle, as I do here in the demo. You do this on occasion, so it may well be a conscious choice based off your reference wheels, but it is something I wanted to call out.

Aside from that, your construction is looking great, and even within the small size you're putting clear effort into capturing not only the outward face of your rims and hub caps, but also those structures' side planes, which helps immensely to make them feel more solid and three dimensional.

Continuing onto the second part of this challenge, we get into texture. Ultimately, that's what tire treads are - they're an arrangement of forms along the surface of another form. As such, it's a good fit for the kind of implicit markmaking we talk about back in Lesson 2 - although being as far removed from it as we are, many students tend to forget about this entirety, and fall back on constructional and explicit markmaking instead. You certainly did too, at first with number 4 - but you clearly caught your mistake and going forward, I can see that you are thinking a lot more about how you can use implicit markmaking to convey the presence of the tire treads you're working with.

To that point, I did notice one issue. If we look at examples like number 22, it does seem that rather than drawing the shadows those textural forms would cast, you may actually be filling in the side planes of those textural forms, which is more similar to form shading. That is, where the whole surface is dark or light based on its orientation. Cast shadows on the other hand are a completely new shape, designed to establish the relationship between the form casting it, and the surface receiving it. The difference can seem really subtle at times, but it is there.

Here's an example I put together for another student. I like to share it because it's a clearer example of this issue, and therefore an easier way to explain the problem.

On 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).

So! That about covers it. By and large you're still doing a great job, and again - I'm thrilled to see that you leaned into the ellipse guide. Access to larger ellipse guides and fuller sets is definitely something we're trying to address currently. Just as we did with getting fineliners and selling them far more cheaply than others, I just bought Jordan (my pen guy) a laser cutter so he can jump into prototyping ellipse guides. While I'm not sure what the timeline's going to be, we're hoping to be able to sell far more complete sets (all the way up to 3.5" in the major axis) for $30 or less. Until then however, your master ellipse template should still be perfectly servicable for its main use in Lesson 7, which is actually more about constructing a unit grid based on cubes.

Anyway, I'll go ahead and mark this challenge as complete.