[sarguy01]

I checked some random brands. I used a 225/60R17 and a 225/55R18 which are about the same width and height. They happen to be the about the same weight. Again, you are moving the weight outward, which takes more power to turn. Did you check the weight of the tires?

The 4 to 1 pound is for unsprung weight. It has nothing to do with changing wheel diameters. Unsprung weight is tires, wheels, axles, brakes, anything under the springs. So, adding heavier wheels will use the 4 to 1, but is different all together from the rotating mass.

Rotating mass. Think of it this way. If you put a one pound weight on the end of a one foot pole and a one pound weight at the end of a two foot pole, which one is easier to lift? The one with the weight at the end of the one pound pole. One pound at one foot is one foot pound of torque. One pound at two feet or two pounds at one foot is the same, two foot pounds of torque required to lift. (We are also assuming this pole has no mass) So, if you go from 17" wheels to 19" wheels and add one pound to the rim portion, the engine must now work harder to accelerate the wheels because the mass at the end of the "pole" weighs more and the "pole" is longer. Add that to 4 pounds to 1 pound ratio for unsprung weight.

Now, since your new wheels are lighter, they may have a rotating mass similar to the smaller, heavier wheels. It all depends on the design of each individual wheel.

Rotating mass really makes a difference. Why do you think slicks are all on 15" wheels? Because who wants to slow down their car in the quarter mile to run 17" wheels? That power that is used to get those wheels moving could be used to accelerate the car faster.