Well, according to this Tyre Size Calculator -

www.carbibles.com/tyre_bible_pg4.html (Scroll two thirds down the page)

The 225/45 R17 has a rolling circumference of 1913mm whilst the 235/55 R17 has a rolling circumference of 2081.89mm, a difference of 8.3%. So using the slightly smaller diameter wheels and tyre combo on the XF would reduce the gearing and the speedo would over-read slightly.

Not a lot of difference in offset, i'd be inclined to pop them on and have a look see, problems usually show themselves at the front, usually by catching the brake calipers or suspension leg.

Obviously the tyres are too small.

The small difference in offset between the (earlier) X type and XF might only be down to a slightly wider wheel to accomodate the extra 10cm of tyre width, i have no idea why 06 on X type gained such a large increase in offset, from 52 to 60 or so.

The correct sizes and offsets for your own wheels will be stamped on the inside of the casting.

Edited by gordonbennet on 01/02/2014 at 15:23