[ttimbo]

It's the change in the rolling circumference that matters to the car's brain, not the diameter. And there's no problem: the rolling circumference of 225/45x19 tyres/wheels is almost identical to 225/50x18 wheels/tyres. But -- really -- this is all your dealer's problem to solve, provided you have evidence of the 18" 566 spec in your order. If the car is being built next week, the dealer ought to be able to get the mistake corrected at the factory.