Wit 20" wheels I have the extended wheel arches as standard. However, from a cleaning point of view I don't like them because I think dirt and mud will get in between the metal and plastic. Has any one removed them and to what benefit.
Really not sure. I wanted to take them off permanantly but, maybe an annual take off and clean would be ok. The same reason why I don't like mudflaps. I keep my cars for long time so have seen rust break through where waater and mud can be trapped.
I removed mine. The front extenders are held in with black clips (9 each side) and two sided tape. The rears are only held in place by two sided tape. The black clips slide off. First remove those. Next use a hair dryer to heat the adhesive and slowly pull the trim off the car. The warmer it is and the slower you pull will reduce the amount of adhesive you'll need to clean off afterwards. Same for the rear except there are no clips.
I removed one side without using the hair dryer for comparison. It isn't necessary but does make it a little easier and leaves less adhesive to remove. I used Goo Off to remove the residual adhesive from the fender. Also, everything is reusable afterwards and can be reinstalled with new two sided tape.
Its a legal requirement that the tread of the tyre must not protrude past the arch was my understanding, the sidewall is not counted (however stupid stretched tyres that disregard the correct/safe fitting for wheel width are a fail anyway)
My mk3 Golf runs TVR wheels that extend slightly past the arches however the camber and tyre choice allows for the tread to stay underneath the arch - it passed its MOT last week at whats considered to be a rather strict test centre (technically the rules are black and white and all centers should be the same)
Looking at my SQ5 i think i could confidently fit 10 -15mm spacers with no issue extending past the arches