None, I have the 18" wheels on mine and I am at a lifetime at 5.7L/100km (41.2MPG). It has been dropping (or increasing if your using MPG) almost daily.
I consistently get anywhere between 4.7L/100km (50MPG) and 5.1L/100km (46MPG) on my 60KM drive to work and 60KM drive home. Usually my drive home is in the 5 - 5.1L/100km mark (46-47MPH) on my way home because there's more uphill driving. It's a slight elevation most of the way home and that shows with my commute both ways. Going to work always shows better MPG. The warmer temps are definitely a factor. Back in Feb and early Mar I was getting between 5.5L/100km (42.7MPG) and 6.2L/100km (37.9MPG). Granted this was when I first got the car and was still learning how to drive it.
One thing I have noticed, is that I get much better fuel economy not using Eco-cruise or regular cruise. When I control the gas pedal I get the best results. Usually lifting the pedal ever-so-slightly on the highway makes a world of difference. The car does great when cruising. Also I never go by the instant L/100km or MPG gauge as I don't find it accurate especially when accelerating.