your milage may vary

[D22369 0]

Your Mileage May Vary
Government to 'Adjust' Its Fuel Economy Estimates in '08
By ERIC PETERS


"Your mileage may vary" is the government's way of tacitly admitting the fuel economy figures it publishes on new car window stickers may not reflect the actual miles per gallon your vehicle will deliver once it’s in your hands.


The figures are, at best, a rough guide -- not a definitive statement -- based on averages obtained during controlled testing. And as many of us have discovered, the government's estimates are often a tad on the optimistic side.


The reason for the disparity between what the government thinks we might get and what we actually get is pretty straightforward: The way we drive our vehicles is often very different from the way government testers do. We cruise at 70-75 mph on the Interstate instead of 55 mph -- knocking down our potential "highway" fuel economy by as much as 5-10 percent. Or our typical "city" driving consists mostly of fairly abrupt (and very inefficient) 0-20 mph stop-and-go driving instead of steady-state 30-40 mph -- likewise reducing real-world "city" mileage by a significant margin.


The current testing procedures used to estimate fuel economy date back several decades -- and haven't been updated to reflect changing driving habits and traffic patterns.


For example, highway speed limits have gone up by 10-15 mph (or more) in many states, following the 1995 repeal of the 55 mph National Maximum Speed Limit (NMSL). These higher speeds have a (negative) effect on real-world highway fuel economy -- but the current tests assume we still live in a "drive 55" world. Similarly, congestion has worsened markedly in and around most major urban/suburban areas -- increasing the time we spend accelerating and decelerating (which wastes energy and thus fuel).


Finally, the tests currently used are skewed because they assume "optimum" conditions -- even temperatures, intermittent use of power-drawing accessories such as air conditioning -- and so on. But cars burn more gas during "cold starts" on harsh winter mornings than they do at room temperature -- and constant cycling of the AC on a 100 degree July afternoon will likewise cut into the "best possible" mileage you might otherwise get.


But new tests slated to go into effect beginning with model year 2008 vehicles should give consumers a substantially more accurate window into how much gas their new car or truck will use in real-world driving -- because the revised numbers will be based on more realistic driving patterns, including higher speed/higher load driving and more frequent use of power-using accessories such as air conditioning.


The expected result of the changes in testing methods will be an "on-paper" drop in fuel economy of as much as 10-15 percent relative to currently published figures -- but this won’t reflect any actual drop in efficiency (all else being equal).


There'll just be more truth in advertising.


For example, under current tests, an '05 Chevy Silverado is rated at 17.8 mpg in city driving. Under the proposed revised testing system, the same vehicle's published city mileage would fall to 13.9 mpg -- which is probably a lot more in line with what the typical owner is getting. The Toyota Camry's projected city mileage would likewise drop from the current 28.5 mpg to a more realistic 24.2 mpg.


One class of vehicles expected to take a major hit is hybrids -- whose "best case" fuel efficiency often founders on the shoals of real-world driving. The city rating of the Honda Civic hybrid, for instance, would drop some 12 mpg -- from the current 48.8 mpg to a much-less-spectacular 36 mpg. This will be a revelation (and reality check) for many people -- who drive their hybrids outside the envelope of the hybrid's optimal operating range.


This isn't to say it's impossible to realize the best-case mileage your vehicle is theoretically capable of. If you drive very moderately (no rapid acceleration; no high-speed driving) under ideal conditions (no sub-zero cold starts, etc.) you might equal (or even beat) the government's currently published guidelines.


But since few of us drive that way in the real world, it's probably a good thing the government is changing the way it does its testing. Better to know what we're likely to get rather than what we might get -- right?


Roy

They say I suffer from insanity.... But I actually enjoy it.

[miked10270 0]

I always looked on "Government" mileage figures as a standardised basis for comparison - nothing more.

For example; If "Car-A"gives 25mpg on Government Tests, & "Car-B" gives 30mpg, then I'd expect "Car-B" to be more economical than "Car-A" in my hands. I wouldn't expect either car to return the exact mileage because I wouldn't be replicating the test conditions in the real world.

Mike.

Taking the piss out of the FrenchAmericans since before it was fashionable.

Prenait la pisse hors du FrançaisCanadiens méridionaux puisqu'avant lui à la mode.

[namgrunt 0]

DOGE RAM 1500
king cab .. 2 wheel drive..auto trans,,HEMI

at 2000 rpm I am doing 76mph and get 18.4 mpg

around town 14 to 15 mpg

..

59 YEARS,OVERWEIGHT,BALDIND,X-GRUNT
LAST MIL. JUMP VIET-NAM(QUAN-TRI)
www.dzmemories.com

[Gravitymaster 0]

In some cases the EPA tests are off by as much as 40%. Thats a bit more than just a YMMV.

[jakee 1,596]

Quote

DOGE RAM 1500
king cab .. 2 wheel drive..auto trans,,HEMI

at 2000 rpm I am doing 76mph and get 18.4 mpg

around town 14 to 15 mpg

Y'know I don't think the purpose of this thread was 'post your mileage', it's about how accurate the testing is.

That said, 18.4 is shockingly bad

Do you want to have an ideagasm?

[rehmwa 2]

Quote

That said, 18.4 is shockingly bad

Not for a big truck like that. It's pretty good.

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[billvon 3,120]

>The city rating of the Honda Civic hybrid, for instance, would drop
> some 12 mpg -- from the current 48.8 mpg to a much-less
>spectacular 36 mpg.

I've had a HCH for three years now, and we average about 46mpg. 38 if we're driving 85mph to get somewhere fast, 55 if we're driving around 60. I've gotten as high as 66mpg on a 130 mile round trip at highway speeds.

So an additional problem is what driving schedule to use, and what sort of driver/protocol is used to do it. If it's me in a hybrid, it's going to come in near the current numbers. If it's my college roommate Gene (the digital driver) then it's going to be half of the published numbers.

>Better to know what we're likely to get rather than what we might get -- right?

The most important thing, to me, is that all tests are done the same way. If you know that all the tests are the same, then a car that gets 30% better mileage than average will still be as good a deal. The worst case is that we start having lots of categories for tests (i.e. bad driver, good driver, old, new, California, Arizona high altitude etc) - because it will no longer be possible to accurately compare mileages.

[Gravitymaster 0]

I mostly agree with you. I do wonder why it is the hybrids fuel economy ratings are so far off reality, compared to other vehicles. If it was 10-15% difference, I could understand it, but 40% raises some suspicions.

[billvon 3,120]

>If it was 10-15% difference, I could understand it . . .

Which is what I see. Perhaps hybrids are more sensitive to driving patterns than older cars? It would be interesting to take two new vehicles, say a Honda Civic Hybrid and a standard Honda Civic, put them on cruise control at the same speed, and have them drive 60 miles on a freeway.

Alternatively, the EPA tests may simply use a more 'ideal' driving pattern, one that maximizes mileage in hybrids but not in others. As the test was created decades ago, it was not likely considered.

>but 40% raises some suspicions.

Like what?

[Gravitymaster 0]

Quote

>If it was 10-15% difference, I could understand it . . .

Which is what I see. Perhaps hybrids are more sensitive to driving patterns than older cars? It would be interesting to take two new vehicles, say a Honda Civic Hybrid and a standard Honda Civic, put them on cruise control at the same speed, and have them drive 60 miles on a freeway.

Alternatively, the EPA tests may simply use a more 'ideal' driving pattern, one that maximizes mileage in hybrids but not in others. As the test was created decades ago, it was not likely considered.

>but 40% raises some suspicions.

Like what?

It makes me wonder if the EPA is skewing the fuel economy ratings to promote hybrids. Why is it they are mostly correct when it comes to gasoline only models but so far off on the hybrids? Why wouldn't the hybrids be tested under the same conditions as gas models? Is their some technological reason I'm unaware of?

[billvon 3,120]

>It makes me wonder if the EPA is skewing the fuel economy ratings to promote hybrids.

A conspiracy? Come now. If that's the case, then you'd have to involve me and dozens of other drivers who DO get near the rated numbers.

>Why is it they are mostly correct when it comes to gasoline only models
> but so far off on the hybrids?

See my previous post. Hybrids may be less tolerant of poor driving technique; the EPA tests may assume good driving techniques. Such poor driving techniques may not penalize standard cars as much.

> Why wouldn't the hybrids be tested under the same conditions as gas models?

Testing under exactly the same conditions may cause the discrepancy; see above.

[kallend 2,150]

Quote

Or our typical "city" driving consists mostly of fairly abrupt (and very inefficient) 0-20 mph stop-and-go driving instead of steady-state 30-40 mph -- likewise reducing real-world "city" mileage by a significant margin.

Traffic lights are the culprit. Traffic lights are evil.

...

The only sure way to survive a canopy collision is not to have one.