That is in the recommended variations chart. I think it's 35-45 If I remember correctly, I recently replaced my wheels. I went with a 35 mm offset which actually brought the wheel out closer to lip of wheel opening. It gave the bird a little wider stance. That measurement is from center to back edge/inside edge. Backwards of what you would think. Check out some of the web sites for wheels and measurements. There is one site that you put your car info. in and a picture pops up of thunderbird, you can even pick color and view each wheel on you car. Happy shopping.
I run(bought car with it) a 45 offset and sold the factory wheels with 60 offset because I like the new ones better. have never rubbed.and it feels really stable in the corners.also people will look at them and wonder why they seem different. I think it gives the bird a beefier look,which is not for everyone
remember if you get new wheels most likely they will need different type lug nuts but your factory spare will need the original type. I replaced spare wheel with a normal rim and tire that uses the new lug nuts