I just ordered some Motegi FF7's 17x7 wheels for my car, which tire size should I go with? I'm probably getting a set of Cooper Zeon RS3-A, should I go with 215/45/R17's 205/45/R17 or what? I don't want it to rub ever. I may lower it 1 inch or so later but it's stock right now.

 

Check out one of our sponsors sites - Tirerack. They have some good information on tire/rim changes.

Simple answer.
1st number- width in mm
2nd number- sidewall as a percent of the width
3rd number- rim diameter

So if you use this. Knowing the stock tire size you can calc the overall diameter. Then for the new rims calc what they would be.