I bought my car with aftermarket 18 inch tires and rims but had to take them off and put the originals back on because they were rubbing and bending the top of my wheel well when I would turn, I really like the aftermarket rims and was wondering if I could fit the 18’s on a 17 inch tire to try and save money on buying new rims entirely.
You mean stretch 17 inch tires onto an 18 inch wheel? no way.
I remember several years ago, Tom and Ray were talking about exactly this scenario with a caller. They said it was impossible, and if somebody were able to do it, they’d like to see the arms on that gorilla 
You cannot put an 18" rim on a 17" tire, but if you’ll visit www.tirerack.com you might be able to find some similar wheels to the ones you like that will fit your car.
You can probably find 18" tires with the same width and outside diameter as the original 17" tires as long as the 18" wheels aren’t too much wider than the 17" wheels. There are size charts on TireRack.com you can use to compare.
What you could do, if you don’t want to tell us the year make and model of the vehicle is to tell us the size of the current 18" tires that are giving you trouble and the OEM tire size found on the inflation placard found on your drivers side door jamb. Then we could give you better advice.