[C3H8]

why wouldn't a narrower wheel decrease rolling resistance? a narrower wheel should squeeze the tyre to be a bit narrower as well, which would slightly reduce the width of the contact patch.
going to narrower tyres and wheels works beautifully to reduce rolling resistance on bicycles, motorcycles, atv's, wheelbarrow's, etc... all of which I have personal experience with.

so why wouldn't it work to decrease rolling resistance on a car? When my current tyres wear out, I had planned on replacing them with skinnier tyres.
Stock is: 195/65-15
My current ones are: 215/60-16
I want to put on: 185/70-16 to 185/60-16 or there abouts.

My car's computer controls the speedometer, and I can reprogram the computer to accurately reflect real vehicle speeds if i change the tyre hight or diameter. Most vehicles esp older ones had non adjustable speedo's or even mechanical ones with a spinning cable. mine is completely adjustable via software so changing my tyre size will not be a problem as far as speedo accuracy goes.