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Old 06-07-2008, 08:37 AM   #99 (permalink)
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Originally Posted by JJW View Post
Am I reading that right? The P215/70/R15 had lower resistance than the 165/80/R13?
NO!! - If I am reading the graphic right.

What this is saying (I think) is that the RRC (Rolling Resistance Coefficient) is lower for larger tires.

RRC is RR divided by the load on the tire. I've been searching for the source document to see how they tested the tires - and haven't found it (so far). But Smithers is well known and well respected in the tire industry, so I'm going to take an educated guess that they tested all these tires at the rated conditions - the logical way to do this.

So a P215/70R15 - which has about 50% more load carrying capacity also has about a 30% lower RRC - which means that the P215/70R15 has more RR - just like you'd think.

But what I think this graphic points to is that large tires could be used in such a way that they would generate lower RR.

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