I have used 20" wheels with performance tires for two years now on my Rover both summer and winter and will do the same on my X5 with the 214 and run flat tires.

__________________
----------------------------------------------
2008 BMW X5 4.8i Sport 20" Space Gray
2006 Bentley Continental GT Mulliner Edition
2006 Lamborghini Gallardo 6spd
2006 BMW 750i Triple Black
2006 Range Rover Sport Supercharged
2005 Lotus Elise Touring-Sold
2001 Lexus RX300 AWD
----------------------------------------------