To easily 3D-print wheels in different sizes for the STEMFIE car, here is a FreeCAD file you can download. If you don't have FreeCAD installed on your computer, you can download it from freecadweb.org/.
Once installed, open this FreeCAD file and adjust the STEMFIE wheels to your desired size. Then, you can select the newly generated file and export it to STL for 3D printing.