When you switch to a larger wheel you have to get into lower profile tire so that the overall diameter stays about the same as original. If the overall diameter increases I would think that it would throw off mileage, the speedometer/odometer and acceleration.
It's funny to see some magazine reviewers claim better gas mileage on cars from year to year and say it's because the manufacturer has gone to larger wheels. In almost every case I've seen, larger wheels from the manufacturer come with lower profile tires and the diameter hasn't changed much at all. Can you imagine 18' wheels with the old 75 profile....wouldn't fit into the wheel wells:-)