A few data points on dimensions and weights:
- GTS 681M - 19X9.5 20.4lb / 20X10.5 24.2lb
- GTS 666M - 19X9.5 24.0lb / 20X10.5 28.4lb
- ZCP 666M - 20X9.0 25.3lb / 20X10.0 27.1lb
- STD 437M - 19X9.0 22.9lb / 19X10.0 24.2lb
When you consider that the front GTS wheel is 0.5 wider than the 437M, the 1.1lb weight penalty is not that bad. Maybe they made the 666M very sturdy.
But I still find the 666M wheels quite heavy compared to the 437M though. I had much higher expectation when BMW advertised the 666M to be "weight optimized"
.