I made some modifications to the original design. The rear wheels were not spinning freely, so I made the rear wheel pin narrower. This made the car run much better. However, I originally thought that bearings would help, so I redesigned the rear wheels and washer so that it can take 6700zz bearings. This was totally over-engineered for this toy and in hindsight, unnecessary. But I did include it for the curious and for future builds if a heavier duty wheel system would help.
I look forward to see what comes out of this community, as this is looking like a fantastic system.