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Kodak · 07-16-2011, 12:58 AM

What are some of the EPA estimates flaws that go unnoticed by most consumers? I'm talking about tangible factors that affect real world FE, but are inadequately represented in the tests.

Here are a few I've been mulling over:

1. EPA highway test averages about 48.3mph, but let's be realistic. Many drive 70+ on the highway. Due to drag and gearing differences there may be vehicles that get similar FE at 50mph, but are very different at 70mph.
2. A top-heavy SUV and a sports car with the same EPA est. may differ in the real world, because the sports car can handle more G's around a turn, and can better maintain momentum (I'm picturing the 40mpg Mustang? story)
3. Different BSFC than the test acceleration (I think ~3.3 mph/s was used)
4. GPH at idle (i4 versus v6 etc.) For real city driving, a difference in idle consumption really adds up. I think the EPA added in more idling when the estimates changed in 2008.

I'm sure there are a few more interesting facts that I haven't considered. The above is what I had on the top of my head.

The estimates are a good guideline, but I just tend to think that there is more to it - even the EPA agrees that YMMV.

07-16-2011, 12:58 AM	#1 (permalink)
Kodak Master EcoModder Join Date: Feb 2011 Location: USA Posts: 346 Canyon - '07 GMC Canyon 2wd regular cab 90 day: 24.95 mpg (US) Thanks: 41 Thanked 39 Times in 24 Posts	EPA estimates shortcomings What are some of the EPA estimates flaws that go unnoticed by most consumers? I'm talking about tangible factors that affect real world FE, but are inadequately represented in the tests. Here are a few I've been mulling over: 1. EPA highway test averages about 48.3mph, but let's be realistic. Many drive 70+ on the highway. Due to drag and gearing differences there may be vehicles that get similar FE at 50mph, but are very different at 70mph. 2. A top-heavy SUV and a sports car with the same EPA est. may differ in the real world, because the sports car can handle more G's around a turn, and can better maintain momentum (I'm picturing the 40mpg Mustang? story) 3. Different BSFC than the test acceleration (I think ~3.3 mph/s was used) 4. GPH at idle (i4 versus v6 etc.) For real city driving, a difference in idle consumption really adds up. I think the EPA added in more idling when the estimates changed in 2008. I'm sure there are a few more interesting facts that I haven't considered. The above is what I had on the top of my head. The estimates are a good guideline, but I just tend to think that there is more to it - even the EPA agrees that YMMV.