I enjoyed other 3D-printed toy cars, but found that the axles snapped easily when toddlers played with them. I created these axles to withstand the roughhousing of toddlers. The stiffener is printed lying down while the wheels are printed with the rim face on the print bed. When these two parts are combined the layer orientations are perpendicular to one another and help to prevent fractures through the axles along layer lines. The images show the quick and easy assembly process which is as follows:

Step 0: Print 1 body, 4 wheels, and 2 stiffeners

Step 1: Put a wheel on one side of each stiffener

Step 2: Place the body over the wheels with the stiffeners

Step 3: Place wheels on the other sides of the stiffeners

Glue may be used to secure the stiffeners inside of the wheels. The stiffeners have been given a built-in clearance of 0.15 mm on each face and should fit snuggly into the wheels. If more or less clearance is desirable, scale the stiffeners in the 2 shortest dimensions only.

This model uses an image which prohibits commercial use: https://www.clipartmax.com/middle/m2i8G6G6A0N4b1A0_vw-beetle-black-silhouette-vw-k%C3%A4fer-silhouette/