I thought the ratings were done on a flat road on the moon where there is
1/7th the gravity in order to get those MPG results.I never thought they were very accurate, I only use them to compare one vehicle with another to get a relative ranking when I do a vehicle purchase.
I remember way back when I used to do my own tune up, timing and all. Now I don't even recognize what is under the hood.
It depends on your driving conditions. Every vehicle I've owned in the last 20 years has obtained within 10% of the EPA ratings. I drive a mix of highway and city, but mostly highway (80%). I tend to get very close to the EPA highway ratings and almost never get anywhere near the lower city ratings.
Matt
The difficulty is in the stackup of assumptions and calculation margins. The MPG protocol, believe it or don't, amounts more or less to "Let's see, we measured *about* such-and-such percent HC and CO in the exhaust, and the catalytic converter efficiency is *about* such-and-such percent, so we can assume that *about* such-and-such amount of CO and HC is coming off the manifold, which would mean that *about* such-and-such an amount of fuel was burned".
Never mind that simply measuring the liquid volume of fuel before and after the vehicle is run is considerably easier, more direct, more precise and more accurate, that's not how it's done.
"I can't drive ... 55"
Gary
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