With a full tank of gas and fully loaded with options the 1M appears to weigh in at 3351 lbs. We ‘ve been told by people in the know that that number is about 120 lbs lower than a comparably equipped 135i. How? The lack of a sunroof certainly helps. But beyond that extensive use of aluminum in the suspension and perhaps the removal of some sound deadening material made it possible.
Keep in mind the 1M features some pretty heavy hardware from the M3; the rear diff, 19 ” wheels just to name two. The fact it ‘s lighter than the 135i is still pretty surprising.