I have accepted that as long as the exercise is completed properly, it does not matter if the lines are strained or suffocating for the resulting picture. The result may not be a work of art or a graphic design, but research material.
The cubes are all in the same plane, which can be limiting. I change the horizontal wheel to vertical from time to time to track mannerisms and prevent them from arising.
I make notes on unsatisfactory points, also about the overall direction of how the drawing was completed. Personally I often seem to complete the circle as a "pincer" motion from both sides, front to back. Such a tendency can then be adjusted.
I have long worked with the exercise without checking how the shape would look in an unified perspective with the shapes receding into depth. The computer animation at the top of the page demonstrates such a result. If the exercise is developed in this direction, it can be noted that compared to the computer image the hand drawn wheels are bulbous from the back "corners".