Bigger Tires - Wider Wheels

[WAC51]

I have a 2004 X3 3.0i Sport.

My existing wheels are starting to flake and the tires are not sealing well, constantly having to re-inflate them.

I have bought a secondhand set of X5 wheels with Michelin XSE tires.

My exisiting wheel/tires are BMW model number 3 411 524 - 18X8J, 46mm offset running 235/50R18

The new set are (not sure of model number, but E70 X5 alloys) - 18 X8.5J, 48mm offset running 255/55R18.

My questions is will they fit without rubbing? If they do rub, is there any benefit in fitting a spacer?

Any help is much appricated.

Thanks