It all depends on the quality of the wheels. Here are some possibilities:
- Decrease in MPG
- Turning is not as crisp
- Wobble at high speeds (if not balanced properly)
- More prone to cracking (depends on manufacture process)
- Car feels heavier in turns
Not sure what wheels you went with but if you are willing to spend a little there are some inexpensive options out there that will help you shed a few lbs in weight per wheel and look good, while still upgrading the size.