Any change in rotating mass or even the distribution of that mass will change a chassis dyno result. For instance, changing to lighter racing discs with aluminum hats but larger diameter rotors often reduces HP readings on a chassis dyno as the mass has been moved further from the rotational axis.

It does boggle the mind a bit because you KNOW changing tires, wheels or such can't affect engine output, but because most dynomometers work by calculating acceleration against the inertial resistance load of the drums (sometimes eddy current resistance is also added) any rotational mass change in the loop can change the result.

You are right, though...there is certainly no effect on engine output. But I'm still going to put GoKart wheels on my SRT and leave you in the dust!