[Rez]

Relevance to the scale only matters if you want scale speeds.

All you need is D=RT. Distance=Rate*Time

If you know how far apart two points are (tape measure), and you know how long it takes the car to travel that distance (stop watch) you can solve for the rate using really basic algebra (calculator).

With a little more math you can change feet per second to miles per hour, or what ever flavor you like your data.