Roostre wrote:My research on the Michelin Premiere A/S has been similar to yours, but it *seems* that those folks that bothered to continue posting results after the tires broke in saw only a very small efficiency hit. A few even reported results equal to the stock Ecopias.
I've run them on our previous cars (2) and found them to be a superior tire for handling and traction. I did not measure efficiency accurately enough to know the impact, but they did seem to coast better than the previous set. Nothing concrete, however.
I've had mine for a little over a year and I am quite happy with them. I had a big hit when I got them, but it was just as the cold/wet weather was hitting the area, so it was hard to tell whether it was more the tires or the weather. By this last summer I was back to hitting 4.5-5.0 mi/kWh on my daily commute (I actually never got higher than 4.8 with the Ecopias). I didn't take detail measurements before or after, but on the whole I cannot tell a difference for warm weather, and never went through a winter with the Ecopias so I have no data there. My 40F dry weather efficiency is down around 3.8 mi/kWh without any heating, dropping to 3-3.4 with wet roads and defroster usage.
On slightly wet roads the Ecopias skittered and under steered around corners, which I hated, while the Premier's stick with confidence. My guess is that on the whole their extra wet weather stickiness makes for a little worse rolling resistance, but it is only a guess.