Otherwise the Honda Insight would have 50lb wheels.

Keep in mind this would be true if you could guarantee you'd be travelling a constant rate of speed for a long period of time. How many people do this? You're at a disadvantage (from a MPG pov) any time you need to accelerate.

Nice try though :)

'05 S4Avant, tip
'07 GX470
'08 Boxster S
Ex:'97.M3;'03.996;'00.S4;'02.S4Avant;'00.S2k;'01.GTI1.8t;'99.M3;'98.A4;'98GTIvr6; '93.CorradoVr6;'85GTI;'00MiataTurbo;'90Miata;'93CivicSi;'85CRXSi;etc.