My car + me (assuming full tank of fuel perpetually)= 1.76 tons
My lifetime MPG=32.8 = 57.7 MPGT
My best trip MPG=48.0 = 84.5 MPGT
My best tank MPG=38.1 = 67.1 MPGT
cibbie with me wearing full gear= .255 tons
Lifetime MPG=51.7 = 13.2 MPGT

Best tank MPG=58.9 = 15.0 MPGT
Guess I better drive the car then...

But I like riding the bike...
Cargo based MPGT makes more sense, and in the case of the bike, it would make it make A LOT more sense.