I don't model 4 individual wheels. We could model all of the wheels, but it would introduce extra complication and would only be important for looking at weight placement, different loading on different wheels, etc. Also, the model does not include ramps. That is an additional topic of its own that we might explore in future articles. By the way, for those of you who read Jack Murphy's articles in Derby Tech in the 80's and early 90's, his computer program was a more detailed model of a derby car.
Lanes can have any width, crown, and crown-shape.
The car has drag, which is dependent on the speed of the car, and includes effects of wind speed and wind direction. That should be all that we need. In engineering, we always start with over-simplified examples to gain some basic general understanding and work towards more realistic examples which have more specific, and thus limited, application. The hill is 1000' long, and the useable lane width is 5'. I've run the calculations for hills with a range of drops, from a very steep hill with 50' of drop, to a very slow hill with only 10' of drop.