I'd also like to see more data. And, if you truly believe there was a difference due to wheels & tires, put the original ones back on and you should return to your previous MPG.

I will bet my left knee on the fact that you did not pick up 20% MPG due to wheels and tires, there were other factors involved. I think if you managed to magically levitate the car off the ground with zero rolling resistance you could not gain 20%. I'm sure wheels & tires help, but not 20%.

-Bob C.

There must be a measurable improvement to lightweight rims, or the VX, HX, Insight 1 and Civic hybrid wouldn't be using them. I trust Honda's (and other makers, too) engineering departments to only make changes like this if there is an improvement.

That's some good rational thinking right there. Same thing goes for the VX's aluminum engine brackets. It's probably something that will fall into the "margin of error" from A-B to B-A testing. But in the long run you'll see differences.

If you drive on flat and smooth highways at steady speeds, I wouldn't think lightweight wheel and tire combos would do much. Dream roads aside though, what will help is the reduction in unsprung weight, the car will lose less forward momentum to bumps....

Although, the usage of them in the mentioned cars could be a consequence of keeping the overall vehicle weight low, it's the unsprung/sprung weight ratio that matters, hence ride and handling may have got unacceptably bad with normal weight wheels. Considering that they were planning on using thin low energy tires also, which are not known for their grip, it may have been an attempt to get back some lateral grip, because lighter wheels wouldn't jounce and break contact so easily. So it may have been a way to make other compromises less "awful".

Then I guess anything gained in less energy to accelerate in city traffic after that is a bonus, and not necessarily the whole object of their use.

My road conditions are as follows:

Lots of hills (I live in the "foothills" of north carolina). About 30% of my commute is 45-55mph on rural highways and the other 70% is at 70mph on Interstate 85. I will wait a few more days to refill (I will have about 140 miles today), but I want to move on to my next mod this weekend. I understand that this is not a thoroughly controlled test with A-B-A conditions as preferred, but I also don't have the time for that. I don't intend to publish a 17% increase in fuel economy based solely on wheel weight. I know that that is not the case. And if I had a set of 13" steel wheels with identical tires I could give a comparison on that variable alone. But since I don't my results are a combination of tire width reduction, tire weight reduction, wheel weight reduction, unsprung weight reduction, rotating weight reduction, total vehicle weight reduction, tire tread pattern and compund change, lowered ride height, and probably a few more.

Regardless, my original question included all of those variables and only asked for guesses as to the change. At the time, it seemed logical to me that all of those changes combined should net some kind of increase, though the actual change due to each might not be definable. Maybe it is not as logical as I thought...