Your car's speedometer works in much the same way as its odometer, except that it converts the angular speed of the wheels to a linear speed of the car, assuming standard-size tires and no slipping on the pavement.
If your car has standard 24.0 inch-diameter tires, how fast are your wheels turning when you are driving at a freeway speed of 58.0 mph?
How fast are you going when your wheels are turning at 520 rpm?
If you put on undersize 20.0 inch-diameter tires, what will the speedometer read when you are actually traveling at 50.0 mph?