Print the two shells with the inside facing the print bed. You will need to include a lot of support material. Simplify3D works best for this, but Slic3r or Cura with optimized settings should be fine as well. I used support with lower density for the most part and higher density for the last 8 layer up to the part. This saves a lot of filament.
The tires should be printed with Ninjaflex or something equivalent to ensure good grip.
Everything else can be printed in PLA.