Weathering Cars

I know most builders do cars in thier pristine show condition but does anyone give them a more realistic used and abused look? I am building a 40 Ford coupe that my grandfoather used to race in NASCAR. This time I am trying to get it looking like the real one with all the dirt and damage. I'm used to weathering tanks but this is the first try at a car. The pic below shows basically the kind of things I am trying to achieve all though the one I am building is a different car, all I have is the original pic and nothing digital but they both have the same damage and dirt pretty much. Any tips would be appreciated. Particualry on getting the tires looking like they have been driving on dirt and the dirty wheel wells.