I took delivery of a 2001 XKR Silverstone in October last year. I ran it on the Winter Wheels until April this year. When switching to the 20" silver Detroit wheels, I have had steering wheel vibration at speeds around 100-120 km/h, sometime lower. After having the wheels re-balanced several times, the garage came to the conclusion that the CATS ECU was malfunctioning and leaving the dampers on the hardest setting which caused the vibration. They claim that they temporarily swapped the ECU with one from another car and it solved the problem. I must say that I am a little sceptical however. They have ordered a new ECU, should take at least several weeks.