Well, theoretically anyway. But in this case the 18s are also wider which means that they have a larger contact area, so that could swing it back in their favor. Tire pressure is also a factor as it will also effect contact area.

In practice, the two tires we're comparing here are so similar, and the variables are so numerous that saying anything certain about which is better for which application is basically just guessing game.

 

saw on i think it was horsepower tv that even if you goto a lighter 18in wheel it can make your 1/4 times higher b/c they said the mass is futher from the center of the spindle and that raises the amount of power and torque to get the wheels moving