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Old 03-29-2014, 07:52 AM   #34 (permalink)
CapriRacer
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Big Dave,

I hope you understand that I am trying to correct a misconception and I'm not picking on you or your post. Just merely trying to get the facts straight.

Quote:
Originally Posted by Big Dave View Post
As rolling resistance data is closely guarded.........
It's more like there are several ways to express RR and there is no agreement which test to use. In other words, different tests yield different results, so unless the tests are the same, you can't be certain of any particular value that is quoted.

And rather than get into a pissing contest with their competitors, they've chosen to be purposely vague.

Quote:
Originally Posted by Big Dave View Post
....., one default you can assume is that the OEM rubber is the lowest RR you are likely to find.......
This is very likely true. I don't know of any tires that have truly low RR values that aren't OEM.

Quote:
Originally Posted by Big Dave View Post
........... This is data the OEM has to submit to the EPA to get an MPG rating..........
Actually, the RR values aren't submitted. The overall vehicle test results are and the tire's RR value as well as the engine's efficiency, transmission losses, etc. all contribute to the value obtained. The tire's RR is just little bit of the overall picture, but the government doesn't know what the RR values are (unless they test them themselves.)

Quote:
Originally Posted by Big Dave View Post
...... and as MPG ratings are often sales points, the OEM has a reason to use the lowest RR tires possible........
Well ...... sort of. RR is part of the technology triangle where traction and treadwear form the other legs. Any improvement in one area is done at the expense of another area. It's a delicate balance that vehicle manufacturers sometimes get wrong - one of the reasons why OE tires are generally considered "poor quality". But OE tires aren't always the lowest RR values possible - sometimes the vehicle manufacturer will emphasize traction in order to impress journalists.

Quote:
Originally Posted by Big Dave View Post
......Keep the skinny tires.
Skinny isn't so much the over-riding factor in RR. There are other things that have a much larger effect.
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