Gotta agree with Bill on this one. I'm designing my own 1/18th on road that I'm building up using my 3d printer. If you have a 3d printer then you might want to check out openRc it's a subpage on thingiverse.com where people post their designs for printing. Structural components would only work on slower moving vehicles, and smaller scale. The larger scale you go the less parts you can 3d print for it. I've only ever printed in pla, but if suppose if you were to try and print, for example, an a arm for a 1/10th car, you would best use abs or carbon reinforced pla. As for weight, a 3d printed part benefits from various ranges of infill so it will be lighter, by design than your typical injection molded part. I had to add weight to my car to get it to run better, even though the chassis I printed extended the wheel base and was 3mm , simply because once the initial wall (of 0.4mm thick) is printed, the inside material is only 50% . It is still very strong (for my uses) but weights less. The benefit to running 3s printed parts is that you can make tons of spares, or redesign the part for a different characteristic for the car. I encourage you to check out openRc and my build here on the website if you're curious. (it's under micro cars)