[Ladogaboy]

Now, I know this subject has been discussed before in other weight reduction threads, but I had a random thought and was curious as to what you all thought about this.

Rotational weight, especially in the reference to performance vehicles, usually is considered separately from standard... "sprung"... weight reduction. I know that most members here have seen only slight improvements from standard weight reduction in their vehicles, and when accounting for rotating weight, the general consensus seems to be that it only really helps in city/stop-and-go driving.

My question is, has anyone tested the effectiveness of decreased rotational weight on combined mileage numbers?

The reason(s) I ask is because the benefits of lowering rotational weight are noticed most prominently in the periods when the vehicle is accelerating, and one of the few things that I remember from high-school physics is that acceleration can come in many forms. For instance, as I am driving up an incline, I am technically accelerating, and I notice the 5 to 10 mpg drop as I am doing so. This is true whenever I am driving up a hill... both in the city or on the highway. Another instance in which my car is technically accelerating is when I am making changes of direction. Sure, much of the "pure" highway driving that I do only involves straight lines, but still I often find myself "accelerating" around curves and corners.

Furthermore, it seems to me that most of the ABA testing that people do only includes relatively straight roads with little to no inclines. To properly test this, it seems to me that you'd almost have to test this modification on curving roads with varying inclines. Obviously, the consistency needed for ABA testing would be more difficult to maintain, but I believe it is possible.

I have been made more curious about this because I know of parts currently available for my car that could potentially lower the rotational weight by 60-90 lbs (depending on how extreme I wanted to go). Now, most of the people who have these parts aren't concerned with changes in fuel economy, so they haven't been tested for that. But in one case, a modification that reduced the rotational weight by 15 lbs resulted in a 3 mph increase in the car's 1/4 trap speed. So it is certainly having an effect in terms of ease of acceleration.

Now I understand that in terms of economy, these modifications might never pay for themselves, but if I am on a quest to have my cake and eat it too, they might be worthy of investment. If nothing else, I could bite the bullet for the team and properly test the efficacy of these modifications in terms of economy... Just a thought.