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Old 01-03-2013, 02:36 PM   #1 (permalink)
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Lightbulb Likely culprit behind low real world MPG vs. EPA numbers? Coast down test by OEM?

Fuel economy follies: Cheatin' or mistaken?


I just came across this article, which is a tale of how the unglamourous coast down test, as conducted by the OEMs, may be where the OEMs are feeding less than accurate info to the EPA test lab?

This can be accidental bad data, but, garbage in, garbage out. The EPA has to TRUST the 'road-load power' numbers that OEMs give it.


The Road - Load Power numbers are generated via OEM coast down testing following a specifc SAE procedure.

The Road - Load Power numbers are then fed into the EPA test plan and systems, to config their dynos to simulate real road use, including aero dynamic drag, RR, weight, etc.

If the numbers are off from OEM, EPA has no way of knowing this, except via coast down audit.

Hyundai has said it was in their coast down test procedure that caused them to state too high MPG numbers.

Maybe this is why the Chevy Cruze has a smaller gas tank? Less mass of fuel, better coast down, better number for EPA to plug into their dyno?

Maybe the Ford C-Max and Fusion 47 MPG claimed situation will get the same scrutiny, with EPA going beyond the dyno and conducting thier own coast down test.

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Old 01-03-2013, 09:36 PM   #2 (permalink)
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I see the author has noted the Prius C as getting 10 mpg below EPA. Would love to know where he's driving it and in what conditions.... That's pretty difficult to do. I mean, I've done it, but the conditions for underperforming like that are nothing like what I'd consider normal.

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coast down test, epa, ford, hyundai, mpg

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