Why winter tires gives better mileage at 15+C

Question

Can somebody explain why my winter set of wheel/tires gets better mileage in almost summer temperatures? At 14-17C+, my winter tires give me 29 avg on a test route, while summer gives a ~24 avg. I expect quite opposite numbers at this temperature. What could be the reason?

I have a VW Passat with 2 sets of wheels/tires:

1. Summer 18 inch with Hankook Ventus v12.
2. Winter 16 inch with Michelin Xice3.

The weight difference is #1 20.1kg vs #2 20.0kg. Circumference difference with current thread wear is within 1 inch.

Answer 1

I would assume for that same reason as eco tyres. As winter tyres typically only start giving decent grip at temperatures below 7 degrees Celsius, the lack of grip at the temperatures you are using them is effectively reducing rolling resistance.

Perhaps you are also subconsciously aware that you'd take longer to stop and have less grip in the bends so have adjusted your driving style to compensate.