Staggered wheels e90 320d

Been offered a set of style 188s for my e90 320d se but turns out they're a staggered set running 225/45/17 front and 255/40/17 rear. Having never swapped wheels before just wondering will this setup compromise the car in any way eg mpg, tramlining etc.
Stock wheels are 225/45/17 all round.
Cheers.

They're the stock tyre sizes for that wheel, so theyll be fine, I don't imagine there'll be any ill effect, though if tyres are cheapo Chinese stuff, or very worn, they'll not handle well

Cheers Don, tyres are part worn pirelli's - some price for the 255's compared to the 225's