Weight measured.
The 17x9.5 front ZR1 with 275/45/17 tire weights 46lbs.
The 15x4 skinney with kuhmo 165r15 weights 31lbs.
So I saved 15lbs per wheel. Hmm not much. But I guess there is much than just a weight, since the the wheel and tire is not as wide, well then better for aerodynamics.
Rear wheels: 17x11 ZR1 with 315/35/17 Nitto weights 58lbs.
Rear 15x10 drag lites with 28x10.5 hoosiers not weighted yet.
Just a little info.

