I believe the overall diameter is almost the same.
Weigh the stock wheel and do your research on the new ones.
Chances are they'll be heavier, but lightweight 18s may not actually weigh more than your stock rims.
Have your suspension been replaced? Wide, low ratio rim/tire combo may highlight weaknesses of a worn suspension.
In short, upsizing is OK if the overall diameter is the same.
Last edited by lszlszx; 10-05-2013 at 10:35 PM.