Jim tries to be evasive, because he knows I have a point, so he beats around the bush.
I believe that he's also running aluminum spacers, his plastic hub rings, extended bolts, a slightly heavier tire, and it's rare that manufacturers claimed weights for anything are accurate, so while he has reduced his rotating mass, it's less than he thinks,
and it's mostly near the axis, which will reduce the benefits.
He's also still on stock width AS tires, which is not at all what I was talking about. I was talking about a true performance upgrade, with wider wheels, wider tires and a real performance tire. It will be tough to end up with a real rolling stock upgrade that weighs significantly less than stock.
And no one is aggressively launching a 400whp GTI on 225 AS tires. I have 2 sets of 245 RE71R's mounted on RSE16'S and a set of 225 FK510's on a set of 7.5" wide Runlites. I have likely 280ish whp and the FK510's can't put it down. The 245 RE71R'S on 8.5" wide wheels will hold fine if launch at conservatives rpms, but barely.
At the end of the day, there's no free lunch. More grip and stiffer sidewalls add weight at the farthest point from the axis. Light rotor and wheels reduce weight close to the axis.