Hi Trevor, thanks for your input with regards to my predicament. At last I have to report that I have had 17" wheels with 235/55 tyres fitted to my XF. I now experience (as you kindly pointed out) a "Softer" ride. Gone is the "Harsh" jolt when going over bad parts of road surface. However I now get some slight sideways movement when going over "White Lines etc" which I can tolerate. I still experience a slightly "Jiggely" ride at times but these items are well worth putting up with rather than the teeth rattling ride I experienced with the 18" wheels.....My Jaguar Dealer has offered to try to sell the set of 18 x 245/45 wheels on eBay for me. Incidently the XF had to be reprogrammed in order to adjust the Speedo etc.after fitting the 17" wheels....I contacted my Insurers who made a note on my file about the wheel change, but it did not alter the premium..............Many Thanks............Billyboy