It sounds like you have one piece of a larger ellipse guide set - they'll come in sets of many different templates covering a wide variety of sizes and degrees. Since these are quite expensive, however, most students opt to get a "master" template which is a single template with many different degrees, restricted to two or three sizes (usually on the smaller end), like the one listed in the Drawabox recommendations page here.

Looking at your wheels, many of these have been constructed quite well (despite only being able to use an ellipse guide on certain ellipses and having to freehand the rest). There are definitely several that fell apart - like 16, 17, 20, 23, etc. for example, and these are mostly due to the elliptical shape itself getting deformed. Make sure you're drawing all your ellipses from the shoulder, applying the ghosting method and ultimately executing your marks with confidence. Larger ellipses are naturally more challenging, and they're that much moreso if you end up drawing them from your elbow.

Aside from that, there are a few things I'd like to draw your attention to. Your first page all features pretty solid constructions, but there are issues when it comes to the tire treads that are present throughout your set. Specifically, tire tread is a texture - it's made up of forms that adhere to the surface of a larger, simpler form. That means that you should be relying on textural techniques (like those covered in Lesson 2) to capture them. Here you've pretty consistently applied constructional techniques - drawing each and every little chunk of the tire treads in wheels 2 and 3, for example, explicitly rather than implying their presence by capturing the shadows they cast. The reason this isn't workable is that it forces you to draw each and every form individually, whereas capturing them with shadows allows us to control the density of our marks, leaving certain areas more sparse and others more densely packed without actually interfering with what is being communicated about the tire tread to the viewer. That is to say, when we draw the cast shadows of these forms instead of their outlines/construction, we're not forced to draw the shadows of each and every form. This is discussed in the section on Implicit/Explicit texture from Lesson 2, and is also touched upon in this section.

The last point on this topic I want to make comes in the form of this diagram. Notice how on the right side, we still get the sense that we're looking at a box form even though there are no internal lines defining the side planes of the form? This is something to keep in mind - you can imply specific aspects of the faces of a given form purely through how its silhouette is defined. This saves us on linework that might otherwise clutter a drawing and make it noisy/distracting - which is another benefit of working implicitly through cast shadow, instead of with lines, outlines, and other "explicit" elements.

Towards the end of your set, you end up drawing certain tire treads more like the example on the left - again, this isn't working implicitly, since you're still drawing on the textural form itself, rather than implying its presence through cast shadows on neighbouring surfaces. That diagram should help illustrate the difference.

Aside from those points, you are still largely doing a good job, and you've got a number of well constructed wheels throughout here, along with some great work on the various rims. As such, I'll go ahead and mark this challenge as complete. Just be sure to keep these things in mind, and consider picking up a master ellipse template for Lesson 7. It will come in quite handy.