Hello, this is my first post. I just bought a 67 plymouth Fury. It has stock wheels, tires, and hub caps. I would like to put on cool looking rim's. my tires say P21575R14 (But I am note sure what this means) I found a guy who has some cool Cragers for sale but they are 15" (I would like to keep my tires since they are new) Lastely I have read on the forum about diffrent width's. (I have know Idea what width my tires are) well thanks for your help in advance and sorry for probley some dumb questions.
Thanks, The new guy

 

To translate the tire markings:
The 215 is the tire width (at its cross section) in millimetres.
The next part is 75 -this is the aspect ratio in percent. This means that the height of the tire is 75 percent of the width. In this case, 75 per cent of 215mm equals approx 161mm and this is the distace you will measure from the tire tread to the mounting bead (where the tire meets the metal wheel).
The final part 14 is the diameter of the wheel in inches. This is the most relevant number for you since this tells you that the Cragars you have seen will not be compatable with your existing tires.

The 'P' prefix simply denotes that the tire is suitable for passenger car use as opposed to for example LT which denotes Light Truck.

While those Cragars may fit your Fury you will have to obtain 15 inch tires to go with those 15 inch wheels as you 14 inch tires will not fit -no matter how much soap you use.
Two choices then: Find some 14 inch Cragars to fit your existing tires and car or find some replacement tires to fit the wheels rims you have been offered.