Devol

I have 17inch alloys on my 2012 Q5 I'm told it's recommended to go two sizes bigger . Is this true can I only fit 19inch alloys. Thanks

Hi Guys newbie :-) Had my 2012 Q5 two days and love it already. When I use the mmi sat nav the top portion of the screen is obscured by a blue line. I thought it was the sky at first. Im working my way through the manual but it does look like a fault any ideas or remedies to fix it I have called the garage who will look at it but its a ford garage :-( thanks in advance Devol