Admin note --
this discussion originally came from here:
http://ecomodder.com/forum/showthrea...age-27384.html
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If you've eco-driven / hypermiled a range cars and have compared the ability of manuals vs. automatics to beat their EPA ratings, then you have probably seen that manuals typically trounce the EPA
city ratings by a much bigger margin than automatics,
even without using advanced hypermiling techniques like pulse & glide or engine-off coasting.
Why is that?
That's what this thread is about.
(Note: we're talking about
city/combined driving here, not highway driving. Don't think because you can trounce a manual's EPA rating in the city that you can necessarily beat the equivalent automatic car in real world driving (cruising) on the open highway. On the highway, it all comes down to gearing, and if the automatic is geared significantly "taller" than the manual, it might win.)
Quote:
Originally Posted by cbaber
It would be interesting to see the EPA tests and how they are done. Obviously the M/T is not being driven to it's full potential.
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I've done a bit of searching on this...
Not surprisingly, test drivers performing an EPA certified fuel economy/emissions on a dynamometer must accelerate & decelerate the vehicle at precisely defined rates.
They essentially stare at a compter screen hanging in front of the windshield and follow a trace, trying not to "colour outside the lines". It's a big video game. (Deviate from the prescribed speed by over 2 mph, and the test is thrown out.)
This is easy with an automatic: Put it in "D" and work the pedals.
When testing a manual, though, the driver is instructed on the computer screen exacty when to upshift or downshift.
Source:
The Truth About EPA City / Highway MPG Estimates
Car & Driver, August 2009, by DAVE VANDERWERP
So there's our answer in a nut shell. And it explains why there's a much bigger opportunity to trounce the EPA in sub/urban or combined driving with a manual than with an automatic.
But what I didn't find (and I'm not going to keep searching right now), is just
how the shift points are determined.
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UPDATE, Nov 13 -- Found the answer. In current EPA testing, shift points are provided by the manufacturer. See post #17 for description & link to source.
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I've found references that at various times in the past, the EPA used:
(A) Pre-1976 ... exclusive use of universal shift points for all vehicles based on speed thresholds: 1st to 2nd @ 15 mph; 2nd to 3rd @ 25 mph; 3rd to 4th at 40 mph (
source)
(B) Vehicle-specific shift points as provided by the manufacturer (which, predictably, led to MPG boosting shenanigans like skip-shifting and/or lugging the engine);
(C) Vehicle-specific shift points that were based on a percentage of max engine RPM or bracketed the engine's torque peak (maybe... that one was part of an old comparison study on the subject);
(D) Shift points based on a vehicle's dashboard shift light/indicator;
(E) Shift points based on research of how actual drivers shifted;
(F) Some combination of the above.
But I didn't find anything definitive for current testing.
Source: EPA-AA-SDSB 81-8
A Summary and Analysis of Comments Received in Response to the EPA/NHTSA Information Request Regarding the Effects of Test Procedure Changes on Fuel Economy
By: James Hourihane, Glenn D. Thompson and Edward LeBaron
November 1980