Can I put different sized rims on car?

No, but it may affect the electronics slightly and your speedometer. I believe the computer will relearn a couple of things and compensate for the different wheel size. Also make sure the smaller rims clear the brake calipers. If not you may need to use spacers, but don't get carried away with spacing. I would say 1/4" maximum. Preferably less. And make sure they clear both front and rear.because the calipers may not be the same size. You can possibly compensate for the slightly smaller rim with taller tires. Your tire shop should be able to help you out with this if you're buying new ones. I have 18" rims on my Cobalt in the summer and 16" in the winter. The car actually sits slightly higher with the 16" rims because the tires are a much taller profile and make up for the two inch rim difference and them some. I've been using this combination for 1 years with no problem.