Originally Posted by ElanC

Let's carry this speculation a bit further.

I think the higher "equivalent weight" of the wheels is because they rotate. When the car accelerates you're giving the wheels rotational momentum, which takes more energy than linear momentum.

Anyhow, the CHC weighs about 2800 lbs. So adding 32 equivalent pounds of momentum increases the car's "weight" by about 1%. For four wheels that's 4%. In the worst case, if all the energy went to acceleration, the change in FE would be 4%. In reality, much of the energy goes to overcoming road friction, air resistance, engine friction, etc. So I find it hard to believe that FE will be affected in this scenario by more than 2%.

One other thing to consider when choosing your wheels/tires. The farther from the wheel's hub, the more rotational momentum. So the effect of the tire's weight is much greater than the effect of the wheel's weight.