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Old 06-14-2020, 09:43 AM   #25 (permalink)
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Originally Posted by GreenTDI View Post
Optimal tire pressure is the key here, I think. A narrow tire requires a higher pressure. Pretty all eco-cars are delivered with narrow rock-hard tires.
But is the label as reliable as it comes to fuel savings. RRC is only one part of the story.
Again, in my case, the 205/45 gets a better score than the 185/60. But I can imagine that a narrower tread weighs less, and also causes less air resistance.

A narrow tire at maximum pressure (= often higher than the wide one) should be more fuel efficient. Despite a higher -theoretical- rolling resistance
I don't think we know enough to say that.

Consider that a 4 psi increase in inflation pressure results in only an 7% decrease in rolling resistance, while a change from a 205/75R15 to a 225/60R16 (same diameter, same load carrying capacity at the same inflation pressure) results in a 3% decrease in RR.

Part of the problem stems from the fact that there are interactive variables. You can't just go wider without compensating for the increase in load carrying capacity by reducing the inflation pressure.

Or should you keep the overall tire diameter the same? - which means decreasing the aspect ratio.

One has to be very careful when making these comparisons.

Further, the range of RR within a given tire size is like 60%. So it is much more important to carefully select the make and model tire than it is to worry about tire size.

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