Have you weighed these rims personally? Or you believe in the stupidity that is posted on websites?
I did personally measure the wheel/tires and it seems in this case, the “stupidity that is posted on websites” is not as far off as one might think… although I only measured the wheel and tire assemblies together:
-rear I got 38 lbs vs 47 lbs for the OE wheel/tire (both 225 tire size)
-front I got 36 lbs vs 38.5 lbs for the OE wheel/tire (not a big weight reduction but going from a 175 to 205 tire)
If we take the rear as the most representative (as it’s the same tire size), it dropped a measured 9 lbs or 4.1 kg for the wheel/tire combo vs calculated (off the internet amounts) for the wheel alone OE 11.5 to new 7.8 = a 3.7 kg drop (no tire difference).
So the greater measured 4.1 kg drop vs the calculated 3.7kg is either the error in the crappy bathroom scale I used (which also only reads to 0.5 lbs) or the tire, which if I believe more “stupidity that is posted on websites” the Pirelli tire is a little lighter than the Bridgestone. I do tend to believe the Fastwheels website vs others as for each wheel size and offset they provide a different weight, so they appear to be directly measuring each size. They also have some other wheels they show as horrendously heavy (29.6 lbs for 17x8), so they seem credible. They may be a bit optimistic, but not too far off.
I think there are a lot of variables in this; my scale, manufacturing tolerances, I’ve seen various OE wheel weights on this forum, etc. In the end, the car feels very different in its response to bumps, with much less energy coming into the suspension. I’m surprised its as noticeable as it is.