EPA estimates shortcomings

[Kodak]

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.

[Old Tele man]

...actually, the EPA tests *do* go above 60 mph, but only for a few minutes--that 48.3 mph is the final / total time average number, not the peak. How many times do people only drive 1-2 or 5 minutes on a freeway?

...what the EPA really needs to provide are "spot" MPG values coinciding with typical highway/freeway speeds, ie: 55, 65, 75 mph, etc.

...we, here, obviously *know* those numbers would "follow" a descending 'constant power' curve, ie: something roughly equaling K = mpg*mph

[jamesqf]

Yet for all the supposed shortcomings, I've always been able to get better than EPA out of any car I've ever driven long enough to figure out what mpg I was getting.

[Old Tele man]

...normally, I would agree with you, but I've found that I cannot even "get" the EPA-estimated 36 MPG value for our 2011 Cruze 1.4LT LTZ with the 6-speed automatic...and, seemingly, neither can most other people!

[bwilson4web]

Originally Posted by Kodak

What are some of the EPA estimates flaws that go unnoticed by most consumers? . . .

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

Actually you can see the problem in the EPA web site:
Fuel Economy

For example, here are some compact cars:

• 49.0(16 vehicles) vs 41 EPA- 2010 Honda Insight (auto)
• 45.4(25) vs 41 EPA (48 EPA pre-2008) - 2003 Prius (auto)
• 42.0(10) vs 33 EPA - 2011 Cruze ECO (manual)
• 38.1(11) vs 34 EPA - 2010 Jetta TDI (auto)

The EPA score is an estimate and not really reflective of the utility of the vehicle.

Bob Wilson

[mnmarcus]

Old Tele Man,
I'm surprised you can't get the EPA. I figured most who post on this site would be able to smash the EPA. Are there some extenuating circumstances?

[SwamiSalami]

Fantastic topic! Thanks for starting this thread.