2011 BMW Z4 sDrive35is

When typical car nuts see that "M" insignia on the trunk lid of a BMW, they almost unconsciously say, "Sweet!" Why? Because they know the M designation means that Bimmer is a posh and powerful beast, tweaked at the factory to a higher level of performance than the standard assembly line fare. But M isn't the only letter BMW uses to symbolize performance. It also uses "S."The S is the brand's