Many people are saying use Dawn Dish Soap as that will help cut off build up of grease, grime, dirt with a soft brush.... Don't oil the wheels as the oil will attract more dirt that you will have to clean off....
What I do is wash the Cars with Dish Soap shake dry then go outside and use my air compressor to blow the water off and out of the Car. It works well, just do not get close to the car while blowing it dry as you can peel paint if the compressor is set too high in pressure. Just use common sense and have fun as you may discover a gem underneath all that dirt.