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Old 06-12-2020, 03:34 PM   #23 (permalink)
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Originally Posted by GreenTDI View Post
How is it possible that wider tires with the same rim size score better on rolling resistance according the EU tire label? For example, I can't imagine that 205/45 is more fuel efficient than 185/60. And yet the first gets an A label and the second gets a B.
Rolling resistance is a function of 3 things: The amount of deflection (basically controlled by the inflation pressure), the amount of rubber being deflected, and the hysteretic properties of the rubber. Let's ignore the last one, because the answer to the question is in the second factor.

Most of the rubber being deflected is in the tread area. A wider tire has a factionally smaller tread width - that is, if the tread width is 70% of the section width, an increase in width of 10mm only results in 7mm wider tread.

But the load carrying capacity goes up in direct proportion to the width.

So the amount of rubber deflected per unit load is slightly smaller = better RRC.

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