The limitations of the ellipse guides are definitely understandable, as is your experimentation to work around it. At the end of the day, getting a proper set of ellipse guides is prohibitively expensive, and for the most part we're still able to explore the core of this challenge with what is offered in a master ellipse template.

Overall your wheel constructions are decently done, though there are a few small issues that I assume was caused by the ellipse guides themselves. For example, the shift in degree is generally going to be matched with a commensurate shift in scale (if the far end gets notably wider, then we also need to be reaching for a similarly smaller ellipse overall). In most of your wheels you've got the far end of the ellipse with that wider degree, but still at the same scale. I assume this is because the smaller ellipse would have been way smaller, and that you decided to work with what you had. Still, worth calling it out.

Now, the main thing we do have to talk about is texture - because this is something that students at this stage often forget about, and you are no exception. That is, they forget about the principles discussed way back in lesson 2, specifically the fact that when capturing texture we do so using implicit drawing techniques, focusing on capturing the shadows each given textural form would cast, rather than outlining those textural forms individually.

Looking at your work here, when dealing with those tire treads, you're focusing more on just drawing what you see - not actually considering the specific forms that are present, and how they relate to the surfaces around them. As a result, we get situations like number 8 where you've just drawn arbitrarily wobbly shapes for each groove, instead of thinking about the actual chunks of tread that stick out from the tire's surface. Of course, what we talk about in regards to observation is important here too - to look at your reference almost constantly, only looking away to draw specific marks instead of working from what you think you remember.

One way to think about texture is that when we draw, say, a cracked mud surface, the temptation is to draw the cracks. But the cracks are themselves empty space. Instead, we have to think about the forms themselves, which are the chunks of mud around the cracks, and to draw the shadows they cast. It's easier to just draw cracks, but at the end of the day the result comes out flat and unconvincing.

While your textures leave a lot to be desired here, that is pretty common. This pit stop before the end of the course gives me a nice opportunity to smack people on the wrist and remind them of things they've no doubt forgotten, and haven't revisited nearly as much as they should have. So, I am going to mark this challenge as complete, but be sure to go back and revisit the material from lesson 2 as you move forwards.