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Old 06-12-2020, 08:12 AM   #21 (permalink)
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Originally Posted by oil pan 4 View Post
I got a set of "LRR tires" that were euro "C" rated.
They killed the range on my leaf.
They got better after a few thousand miles.
Need up replacing them with new energy saver A/S tires. Those energy savers at 36psi appeared to be as efficient as the worn out ecopia tires at 44psi.
Thatís good news to me, Iíve got Ecopias right now, planning on replacing with energy savers.

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Old 06-12-2020, 08:15 AM   #22 (permalink)
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They also skip it on commercial vehicles.

https://www.oponeo.ie/blog/everythin...ing-resistance.

In Europe there are loads of tyres being sold that have "ECO" in their name yet only have E and G ratings. You really have to do your homework when buying tyres.
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Old 06-12-2020, 03:34 PM   #23 (permalink)
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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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Old 06-13-2020, 11:25 AM   #24 (permalink)
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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
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Old 06-14-2020, 09:43 AM   #25 (permalink)
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Quote:
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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Old 06-14-2020, 10:18 AM   #26 (permalink)
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Unless I'm misunderstanding something, it seems like you two are talking past each other and post 24 and 25.

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