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Originally Posted by Tim
I think weight will be the biggest factor. I've done a lot of research on my stock 03 wheel setup, as I'm about to replace both wheel and tire.
Stock 03 HCH wheel is ~ 15lbs. I say "about" because Honda was unable/unwilling to part with the actual number. I found the 15 lb value on an after-market web site about 4 months ago but I cannot find anymore.
Stock Dunlop SP 20 FE 185/70R14 is 17.6 lbs (from Dunlop).
Total whell setup is 32.6 lbs.
I've read that 1 lb of unsprung wheel weight (weight of your wheels) is equal to about 8 lbs in the car. So cut your wheel weight by 4 lbs and you're "carrying" about 32 lbs less in the car. All research I've found said that reduced wheel weight will help FE, but none say by how much. Conversely, none will quantify how a heavier setup will hurt.
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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.