Hi Tom
They're the 15" 7-hole 175/65 R15 wheels that come as standard on the Cooper (here in the UK at least). The tyres were going to be the standard Pirellis as a control tyre, but Mike Cooper was saying on Friday that they've just struck a deal with Dunlop to sponsor the series, so we'll all be having those as our control now instead.
Offset? Dunno
Why do you ask?
Andy