So one of the reasons I like putting this challenge here, right before Lesson 7, is precisely what you already identified. Students always (or, I guess arguably almost always) forget about the textural principles from Lesson 2. But it seems very much that despite your apologies, you most certainly did not! And I'm almost disappointed, because it means I have far less to comment upon, but I can at least talk about how I'm not gonna be smackin' you on the wrist, 'cause you've done an excellent job of not forgetting like everyone else.

Starting with your wheel constructions, you're making effective use of your ellipse guides. I'm pleased to see that your wheel constructions aren't always simple cylinders - you're capturing that curvature through the middle quite nicely, even in cases where you're skipping the central ellipse, and as a result the wheels don't feel static or overly rigid. You've also done an exceptional job of drawing this wide variety of rims - a lot of which were reaaally complex.

When it comes to the tire treads, the ones with shallower grooves are pretty much free to be captured however. You can get away with using a lot of linework, and it still reads just fine (like 23 for instance) - but as soon as you get into the really chunky treads, most notably things like 10 and 13, that's where the rules of implicit drawing come into play, because it's just too easy to end up with a really noisy, attention-grabbing (in a bad way) result. After all, you don't want your tires drawing attention away from whatever your actual focal point is meant to be in a larger drawing.

Throughout a number of these, you've shown considerable skill in manipulating those shadow shapes, diminishing the overall noisiness, while still conveying ample visual information to the viewer, allowing them to understand what each tire would feel like to the touch. If I had any complaints at all, it'd be that in very limited cases - like 17 - you get just a little more erratic in the shapes of the actual tread forms, and it breaks the manufactured impression that we'd usually want with something like this. But hey - mistakes happen.

All in all, I'm very pleased with your results. I'll go ahead and mark this challenge as complete.