All things considered, despite the small ellipse guide and having to freehand a good deal of these, your work came out pretty well. There are a few minor points I'm going to address, but all in all your work is well done.

On this page, I noticed a number of cases where you drew the middle ellipse to be quite large, but didn't actually bridge the ellipses along the extremities to it, instead resulting in something of a cylinder with a ring around it (like the top right of the page, for example). Remember that construction is all about adhering to the decisions established in previous phases. Meaning that if you draw an ellipse that is larger than you intended for that center one, that is what will serve as the widest point of your tire/wheel. You cannot change your mind after the fact, even if it means deviating from what you were using as reference. Otherwise you end up with these kids of contradicting, distracting marks.

Overall you do a pretty good job of focusing on capturing cast shadow shapes when implying your tire tread textures towards the beginning, but later into the challenge - like the dump truck wheel (14), the pneumatic tyre (11), and so on you fall back into relying somewhat more on outlining textural forms instead. While I know you understand the concept at hand, there is value in sharing this diagram. Basically when you have a textural form, it's easy to make the mistake of actually filling in one of its side faces to distinguish the different planes of the form more directly. Knowing that you want to be working with shadow shapes, one might think more in terms of filling in the faces that exist for this reason. I can see a touch of it in the dump truck wheel, for instance. Don't. Instead, make sure that the silhouette of the form that is being implied isn't just flat - in the way it is shaped, try and imply the presence of top/side/front/etc faces.

On the right side of the diagram, you can see how the silhouette gives us a sense on its own of how the form itself is three dimensional, and then the shadow the form casts establishes the relationship between it and the surface against which it rests. On the left side, we're given no such relationship, and the form ends up feeling more flat and simplified.

The last thing I wanted to mention was in regards to your skateboard wheel (22). Here you filled in a surface of the form with solid black. Often students do this when they see something that is actually black in their reference, and so something in their brain tells them, "this is black - our drawing will be more accurate if we can capture the black in our drawing too, because we're using a black pen". Since we don't do the same for things that are red, blue, yellow, brown, etc. it creates a "special" case that doesn't actually make much sense, and breaks the conventions used across the drawing as a whole.

Long story short - the only things you should be filling in with solid black are intentional, designed cast shadow shapes and nothing else. Ignore all local colour in your reference image and treat the object as though it is all a solid, flat white.

So! all in all, your constructions here are coming along well. You will probably find that your ellipse guide will still be adequate for Lesson 7, so definitely keep it handy. I'll go ahead and mark this challenge as complete.