Originally Posted by
Canoehead
I used to believe this too, as an avid cyclist and user of big apples, fat franks, and 2" marathon supremes. Someone on this forum, though noted the difference between a bias-ply bike tire casing and a radial car tire - apples to oranges, and wider tires are not more efficient on a car. On a bike, the wider tire is only more efficient for rolling resistance at the same pressure. The narrower tire can run a higher pressure, and will also have less mass, so acceleration will be improved.
As for car tires, wider tires do have more friction, which is good for handling, but uses a bit more energy to both roll and due to greater frontal area (aerodynamics).
My winter tires use considerably more gas because they are made of a softer rubber.
I've dug around in EU fuel efficiency labels, and while the difference insignificant, in general wider Michelin tires were more efficient, in some cases enough to go from C to B category. It is inconclusive, b/c in case of Michelin they have different versions of the tire, and you may also have the pattern change going from one size to another.
Now I agree with you that radial tires are completely different animal, and the difference isn't that great anyways.
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View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)