Happy coasting indeed!
After 4 years, I finally got around to sticking the "winning" Bridgestone Potenza RE92's on the Firefly. (Because the car that
was wearing them --
the ForkenSwift electric car, top photo this thread -- was retired last year).
Despite the presumably worse aero of the slightly wider tires (165 vs. 155) plus air-blender alloy wheels vs. the car's stock, smooth-ish 13 inch wheel covers, the car got much better mileage on a round trip (back roads) to a cottage:
- 76.8 mpg US (Goodyear Invicta) round trip
- 82.5 mpg US (RE92) round trip
Notable: that was with a 3.2 km/h (2 mph)
higher average speed on the RE92 trip. (Similar weather & traffic conditions ... mostly deserted back roads driving, 87 km / 54 miles round trip.)
(Note: the RE92's have a ~1.4% smaller circumference than the Goodyears. I didn't apply this correction to the speed/distance figures here. Even corrected, the MPG % difference is much larger than the measurement error.)
Most of this was driving with load (DWL) on rolling terrain, but I definitely made use of the obviously better coasting ability of the RE92's when approaching most turns & stops (engine off).
Of course, in fairly typical ecomodder fashion, I changed more than one variable:
the car also has a brand new air dam on it. So I can't say how much of this improvement is from the tires alone. It seems unlikely it's all from lower rolling resistance. (But I plan on A-B-A'ing the air dam...)