EPA numbers explained!

[daniel]

I suddenly realized, in a flash of inspiration, what's up with the EPA numbers, and why they're so much farther off for the Prius than for other cars. And why most people don't get those numbers, but some do:

The Prius is unique among cars in its use of an inefficient rapid-warm-up cycle. We all see those 25 to 30 mpg figures for the first 5-minute segment, and unless you are driving a long distance, that warm-up segment pulls your average down.

But the EPA tests cars fully warmed up. The EPA, therefore, intentionally or not, has gotten the car into Stage 4 operation, and left the warm-up cycle, with its low numbers, out of the equation.

We could all get better mileage averages if we left out the first 5 minutes of every drive.

That understood, the EPA test is done under favorable, but not perfect conditions, so people with long enough commutes take less of a hit on average from the warm-up, and if their conditions are good enough, can exceed the EPA numbers enough to surpass them even with the whole drive averaged in.

It's the Prius's unique warm-up, and the fact that the EPA leaves that out, that account for the discrepancy.

(This will be my last post for a few days. I'm taking a trip. Not driving, though. I'll be in Albuquerque to see the play Zoot Suit because I've got family involved in it.)

[KMO]

This is one way in which the European tests are more realistic. They are done from cold, the urban cycle first, then going straight into the extra-urban cycle.

[hdrygas]

D'ooh Administers dope slap. Thanks!! Why is it always so clear when someone points things out to you?

[ken1784]

<div class='quotetop'>QUOTE(daniel\";p=\"42141)</div>

But the EPA tests cars fully warmed up. [/b]

It looks it is not true.

http://www.fueleconomy.gov/feg/info.shtml

" the cold start, which is similar to starting a car in the morning after it has been parked all night"

Regards,
Ken@Japan

[bruceha_2000]

Originally posted by ken1784
\" the cold start, which is similar to starting a car in the morning after it has been parked all night\"

Ken, your fact is correct but you missed a lot of the detail. Are you running for the U.S. presidency? ;-)

Here is more of the text:
<quoted>
Two kinds of engine starts are used: the cold start, which is similar to starting a car in the morning after it has been parked all night; and the hot start, similar to restarting a vehicle after it has been warmed up, driven, and stopped for a short time.

The test used to determine the city fuel economy estimate simulates an 11-mile, stop-and-go trip with an average speed of 20 miles per hour (mph). The trip takes 31 minutes and has 23 stops. About 18 percent of the time is spent idling, as in waiting at traffic lights or in rush hour traffic. The maximum speed is 56 mph. The engine is initially started after being parked overnight. Vehicles are tested at 68 F to 86 F ambient temperature.

The test to determine the highway fuel economy estimate represents a mixture of "non-city" driving. Segments corresponding to different kinds of rural roads and interstate highways are included. The test simulates a 10-mile trip and averages 48 mph. The maximum speed is 60 mph. The test is run with the engine warmed up and has little idling time and no stops (except at the end of the test).
</quoted>


Both of these paragraphs show the fallacy of the results for most people.
First, 68F-85F is reasonable where I live for about 20 days a year. Granted the summer lows aren't WAY below 68F. but the rest of the year? I saw the "EPA avg" temps for the last time until May or June before I even got my car.

Max speed in the city of 56 mph?? Anyone doing that better be related to the cop that pulls them over.

Max speed of 60 mph on the rural/interstate? There are less than THREE miles of interstate in VT that are posted at 55. The rest are 65 and you'll soon see the rear end of pretty much every car you see in your rear view mirror if you stick to it.

I know they haven't been updated for a long time, and have issues for hybrids, but they aren't even reasonable tests for 'regular cars'. Hell, if they are simulated, how hard can it be to modify the tests?

[DaveinOlyWA]

so how does any of this explain why the EPA's numbers are LOWER than mine???

[ken1784]

<div class='quotetop'>QUOTE(bruceha_2000\";p=\"43891)</div>

Ken, your fact is correct but you missed a lot of the detail. Are you running for the U.S. presidency?  ;-)[/b]

Hello Bruce,

I just commented the part of Daniel's sentence was not correct.
That's all. No comment about the adequacy of the EPA tests.

Regards,
Ken@Japan

[bruceha_2000]

<div class='quotetop'>QUOTE(DaveinOlyWA\";p=\"43930)</div>

so how does any of this explain why the EPA's numbers are LOWER than mine???[/b]

Um, I don't know, maybe one of these?[list]Add others as you like. :-)

[DaveinOlyWA]

sorry bruce... just being sarcastic

actually the real reason is that on average 11% of gas pumps are inaccurate.

using the on board computer, i have surveyed the pumps in my area until i found what i believe is a pump that gives me more for my buck.

after all, just because 11% of the pumps are inaccurate doesnt mean they all short you. in a test of local stations this past summer, KING-5 TV found that the pumps that shorted you did out number the generous ones 2.5 to 1 but that means that gasoline benefactors are available for the finding.