[Christ]

a 205/40R16 often will have less rolling resistance than a 175/70R13.

The contact patch is 30mm wider, with more frictional area as a result, but you're going from 122.5mm of squishy sidewall on the road side of the tire to 82mm and much stiffer sidewall (Z rated tires).

Traction is not compromised, Rolling resistance is still less. Ride quality on the other hand... well, that's a problem with nearly any 40 series tire.

From what I can tell about rolling resistance from comparison of tires, most of the resistance comes from flex in the rubber compound of the tire... therefore, harder compound tires should flex less. Lower profile tires also flex less, so it stands to reason that even though you have a larger contact patch, you're still saving on RR.

Someone please correct me if I've misconceived something here.