Originally Posted by MOFSTEEL
^You're forgetting about wheel+tire weight.
Larger wheels plus tire combinations typically weigh more than smaller.
In this case, the 18 inch Michelin Latitude Tour weigh 36 lbs. The 20 inch Goodyear Fortera weigh 34 lbs. I expect the 20 inch wheel to weigh more than 2 pounds more than the 18 inch wheel.
I agree that the differences in weight between the two will be very small.