if you want efficiency (as in saving gas) you want a narrow tire like 195/55x15" or 185/65x15". Less contact on the ground means less rolling resistance.
The lightest wheel I've seen are my 15x7" Enkei RPF1s which are 9.5lbs each. For tires you want like all season radials (less sticky) instead of summer only type tires (stickier). But you shouldn't put a 195 wide tire on a 7" wide rim.
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