I also weighted the standard wheels today, so the weights where:
Standard 17's with part worn 205/40 pirelli P zero's- 18kg
Pro race 3's 15's with new 195/50 michelin pilots - 15kg

So that's a saving of 3kg per corner minimum as the standard alloys was part worn tyres and also no center caps, can't remember the calculation exactly,think it's the rotation mass at 4:1 so that in theory means a static weight saved of 48kg. Although that sounds awefully high ratio 4:1?