Looks good! Does this affect the mpg (or L/100km) calculations?
The overall diameter is very close to stock, so the calculations should not be affected much.
The mpg may actually go down because of increased rolling resistance though.
Call me old fashioned ("You're old fashioned!") but after a certain point it starts looking silly to me. Those 20s are past that point. And is the ride really still any good?
You're going to have to run those at ~42psi to match the load rating of the stock 225/50R18 at 36psi. Yes 36 psi is for max load but running 20s much lower than 42psi will make rim damage much more likely.