Yeahhh it's always gonna be tricky when stuff overlaps. Minimizing that (Ex. by cutting off the upper parts of the bigger wheels) might help? Also with the front wheels you might've been able to actually reduce some of it by disabling double-faced drawing so they didn't render on the opposite side.
But yeah the rendering quirks are def the most frustrating part of picoCAD. The model still works great despite them tho!