Can anyone help trying to fit new 20 inch wheels to my XF 2010 Portolio. Already on 20,s and running on 255x35x20 tyres. but very hard . has anyone ever fitted a 255 x 40 height x20 to improve ride quality. afraid to order tyres incase of rubbing or lights on dash etc. Any Advice would be appreciated. its says somewhere that the maximum rolling is 27 inches nut im still worried about dash lights !! speedo traction control etc ??? thanks Roger

 

255/30/20 is 27" diameter and 255/40/20 is 28" diameter so 1" bigger diameter or 1/2" taller in the wheel well, plenty of room given the stock XF is on stilts.
28" is 3.7% more than 27" which I very much doubt will effect the traction control or ABS etc.
Also it will cause your speedo to "under-read" by 3.7% but given that the XF speedo over-reads by around 6% anyway it will bring the speedo closer to accurate.

 

Tell your insurer!! They may well not care but chances are if you don't tell them then you'll be uninsured (you are strictly liable to tell them).