[Ecky]

I forgot to give you a number!

The delta between winter and summer tires was around -2mpg, but the winter tires had a failing battery AND the dataset was very small, so I wouldn't take much stock in that number. They might actually not be a fuel economy loss over RE92s at all. Nokians are pretty kick-ass tires.

The delta between winter tires with a failing lead acid and winter tires with supercapacitors was ~+8mpg. Again, small dataset and the failing battery makes the numbers of questionable usefulness.

Probably the number you can trust most is that switching from summer tires with a lead acid to winter tires with supercapacitors was worth an improvement of approximately 5mpg, or 10%.

EDIT: Let me throw out that one outlier, which was basically the day my battery failed, and see how the chart looks.

EDIT2: Taking out that lone datapoint, winter and summer tires are very close to each other, and supercapacitors provided a ~5mpg improvement. But, this is based on a VERY small data set.