Length, Width, Clearance
1. The maximum overall width (including wheels and axles) shall not exceed 2-3/4 inches.  

2. The minimum width between the wheels shall be 1-3/4 inches so the car will clear the center guide strip on the track. 
3. The minimum clearance between the bottom of the car and the track surface shall be 3/8 inch so the car will clear the center guide strip on the track. 
4. The maximum overall length shall not exceed 7 inches.