Starting with the structural aspect of your wheels, by and large your work here is done well - you're including in many cases the curving profile that helps to imply the "inflated" nature of the tire, giving the impression that it'll land with a bounce if dropped, rather than a heavy thunk. One thing that did catch my eye however was the tendency towards working with different pens within the same drawings. While not explicitly stated in the instructions for this challenge (though it is in Lesson 6, the general policy in Drawabox is that your linework should not employ multiple types of pens, as this encourages tracing back over existing linework extensively - a process that causes us to focus more on how those marks sit on the flat page, rather than how they represent edges in 3D space. It is also discussed further here in Lesson 2. The only case where switching tools is permitted is to fill in cast shadow shapes, which would already be designed using the main pen.

The reason I'm mentioning this is that when you do go back over your lines, it tends to be quite sloppy, with cases like number 8 standing out in this regard. There's really no need to go back over them in this exercise, so in the future stick to the underlying linework.

Continuing onto the textural aspect of this exercise, it's fair to say that being how far removed we are from Lesson 2 (where we first touched upon the concepts of implicit markmaking and how to approach conveying texture), this challenge is intentionally placed here as something of a trap. Many students simply forget those concepts, and instead of refreshing their memory on it, more often they'll just wing it. It does appear that you've fallen into this trap as well, as you've relied quite heavily on explicit markmaking in one form or another.

The thing to keep in mind is that, being that these tires treads are very much textures - in that there are forms that run along the surface of a larger object - so we should not be drawing those forms directly, but rather we should be implying their presence by drawing the shadows they ought to cast. We go over this in this section, but the notes here may also help refresh your memory on exactly how we go about determining the shapes of those shadows.

It's easy to end up conflating cast shadows with form shading (and as a result, filling the side planes of your forms in with solid black, which I'm seeing more often in your work), but it all comes down to thinking about how the marks you're making relate to what you're trying to depict. It's also worth noting that when floating in isolation like this, these wheels can take on way more visual complexity (which inevitably results from more explicit marks). The reason we still want to use implicit markmaking here is because when the wheels are drawn as part of a larger vehicle, this density of visual information will turn them into focal points, whether you mean them to or not. This hinders how we are able to control the compositional elements of a piece, to direct where the viewer's eye ought to go and how it should move around.

Instead, as shown here on this example of african bush viper scales, working implicitly allows us to increase or decrease the amount of ink that's being put down on the page without physically changing the nature of the texture being communicated.

The other thing I wanted to address are cases where our textures are made up of shallow or narrow grooves. These cases can be especially tricky because we're prone to treating the thing we can name - the grooves themselves - as though they're the textural forms in question. Of course they're not - they're empty space, with the textural forms being the walls that rise up around them, casting shadows onto each other and onto the floor of the groove itself. While the distinction can be very small, and we can even get away with just drawing the grooves themselves in many cases, it still professes an incorrect understanding of the nature of the forms at play.

Here's a diagram that goes over this concept.

Now, as the "trap" was intentional, I don't hold it against students and assign revisions based on that. I'll be marking this challenge as complete, but do be more mindful of how you're using your tools. If you're inclined to deviate from the instructions in any way as a result of how your tools are panning out (so for example, the wheel challenge specifically said to do it with a ballpoint pen, if yours wasn't working out right and wanted to switch to a fineliner) it's always better to ask first, rather than pushing ahead and announcing your deviations later.

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