I've found for a long time that Michelins tend to have great wet grip if gently taken up to maximum loading, but if driven harshly they let go easily.
What size tyres have you got and what model F55? Nowadays the Cooper on 15" wheels must be be short of traction now that it's got a turbo with lots of low end grunt.
What size tyres have you got and what model F55? Nowadays the Cooper on 15" wheels must be be short of traction now that it's got a turbo with lots of low end grunt.