Steady State Speed vs Fuel Economy results

Discussion in 'General' started by seftonm, Mar 22, 2014.

  1. RedylC94

    RedylC94 Well-Known Member

    OK, my comment was admittedly anecdotal, and possibly slightly exaggerated, but only slightly. It had nothing to do with EPA ratings, or the '15 LaCrosse in particular, or your curious obsession with hypothetical "crossover" speeds. People who are far from hypermilers and have no reason to lie report numbers near this Camry's on highway trips in older big Buicks (and similar cars) often enough to believe it wouldn't be a fluke.

    As for why the unusual low-speed result??? Transmission programming seems the most likely primary excuse, shifting out of top-gear lock-up to spare hypersensitive owners from feeling low-speed engine vibration. Then there are Charlie's whacko theories ...
    xcel likes this.
  2. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi RedylC94:

    The EPA highway crossover speed is possibly the most important result from these tests and it has nothing to do with obsession. If you have a graph, calculating a linear derived EPA highway crossover speed is 5-minutes with y=mx+b. From the final two results, calculate m, derive b, plug in y for the x crossover. If vehicle A we tested crosses over its EPA at 50 mph and another vehicle B crosses over its EPA highway at 79 mph, which EPA highway result was gamed and which EPA highway result was not?

    Will you get more distance/dollar from your pump visit with a midsize vehicle A with a 23/34 mpgUS city/highway rating that crosses over at 74 mph or another midsize vehicle B with a 25/37 mpgUS city/highway rating that crosses over at 59 mph? Vehicle A is the more efficient choice despite having a significantly lower EPA highway rating. The generated graphs and crossover is the only way I know how to make these conclusions. If a vehicles crossover is 66.5 to 71 mph, its EPA highway result is pretty solid in my book. Below and someone may have been playing with their products numbers. Above, the consumer benefits.

    Remember the 44/40 rated Prius v vs the at the time 47/47 rated C-MAX? The (2) graphs plus the Prius liftback control told the story.


    Ford’s 47_mpg City/Highway/Combined Hybrid Ratings Ring Hollow

    Speed vs. Fuel Economy comparison results


    The C-MAX fell below its EPA highway rating of 47 MPG at 60.9 mph (calculated straight-line interpolation)

    The Prius v fell behind its EPA highway rating of 40 MPG at 72.7 mph (calculated straight-line interpolation) and clear off the chart!

    The Prius Liftback fell behind its EPA highway rating of 48 MPG at 68.1 mph (calculated straight-line interpolation) and mirrors most other vehicles we have tested


    The 2016 Toyota Camry XSE was not shifting or slipping as the steady tach was right where it was supposed to be at all speeds. The 50 mph result was just as locked in as the 70 mph runs per the tach. If it were not locked up, I would have expected to see a 1 to 200 RPM swing or more and I did not see that. NVH is a good guess but I did not experience that at 50 mph either?

    Last edited: Oct 16, 2015
  3. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    I appreciate the "obsession" with cross-over speed.
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  4. phoebeisis

    phoebeisis Well-Known Member

    Very mildly wacko by my standards
    I have been MUCH MORE wacko in the recent past

    implausible for #1
    #2#3 reasonably plausible
    #4 maybe not

    1) car aero setup becoming more favorable as speed increases-unlikely but not quite wacko

    2)Ignition timing retarded at 50 mph-and top gear about 1300 rpms-not that unlikely-at "some load"
    and at low RPMs knock tendencies increase-so ignition timing decreases-dropping FE

    3)Rich mixture-see 2-rich mixture decreases KNOCK-drops FE-

    4)Fuel flow "meter" being less accurate-in the under one liter per hr range-not likely-but possible it would be "off" in just one direction-not likely
    2&3 are probably "right-ish"

    1300 RPMS top gear 50 mph-would have been knock and lugging range not long ago-
    dropping timing and richening mixture would decrease knock
    The lugging-well it is something else-
    The SQUAT and nose down attitude 50 vs 55-was more a joke than serious

    PS- The steady 60 mph is a GREAT indicator of inherent FE(hy and city).Dials out driving style.

    The HY EPA SPEED crossover-very useful
    1)predicts ease of getting EPA hy and city- or in our case-better than EPA
    2)indicator of GAMING EPA test to get better numbers than you deserve-those Fords back when-CMAX etc
    3)Might have indicated that VW was cheating-but TDs do cross higher than spark anyway-they have a bigger "higher load but lowish RPMs" efficiency advantage-which is why they are such good tow vehicles
    Last edited: Oct 16, 2015
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  5. RedylC94

    RedylC94 Well-Known Member

    If our goal is to evaluate the solidity of a car's EPA highway rating, the only certain way is to re-do the actual test and compare results, which is impractical for most, so we're talking about comparing results of complex variable-speed tests to results of relatively simple constant-speed tests. There are multiple ways that comparision could be summarized, of which your "crossover" interpolation (or extrapolation) is one, albeit a curiously indirect one. Would someone shopping for a car and interested in minimizing everyday fuel consumption find it more practical and helpful to learn that a model is capable of exceeding its EPA highway number by 34% at (for example) 60 mph, or to learn than it can equal the EPA number at 72 mph?

    That said, steady-speed numbers at various speeds like you report are far more valuable than the EPA highway result, because they're easier to understand, make the correlation of speed with consumption clear, and are harder to game. What a car actually can do is more interesting than what EPA says about it, anyway.

    Interesting about the "locked in" tachometer. Did it drop in direct proportion to car speed between the 2nd lowest and lowest test speed? If not, that would show the transmission picked a shorter ratio.
    Last edited: Oct 17, 2015
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  6. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi RedylC94:

    The crossover gives you an idea if the OEM was cheating or not. We still see it even today.

    Regarding the RPM, 5th gear from the Camry XSE has a rather large jump at 45 mph between 5th and 6th coming up from 1,400 RPM to ~ 1,750 RPM.

    At 60 mph, the tach read 1,640. At 50 mph, it was a steady ~ 1,375 RPM.

  7. phoebeisis

    phoebeisis Well-Known Member

    Crossover-and 60 mph mpg
    also might broadly hint that a vehicle needs a redo
    The poor 2.7 F-150
    20 mpg at 60 mph-case in point
    Perhaps that truck "had something wrong with it"
    I could certainly make a WACKO-ISH suggestion or two-and I will
    dragging brakes alignment HUGELY SCREWED

    Anyway it did 20 mpg at 60 mph-should have done close to the 30 mpg of the 3.6 Dodge
    so something was waaaay off

    1640 RPMS at 60 mph-4 cylinder
    Things have changed
    our 2001 Prism/Corolla did 2800 rpms at 60 mph(it was the cheaper 3 speed AT)
    Decent mpg 37 mpg at 60 mph or so-despite all the RPMS

    "just" the 60 mph mpg- would be enough to reasonably predict relative MPG "goodness" city and hy

    Cars/trucks that beat their competition at 60 mph-beat them everyw
    xcel likes this.
  8. RedylC94

    RedylC94 Well-Known Member

    1) Makes about as much sense as the guys who claim "My BMW (or F-250 or whatever) gets better gas mileage at 75 mph than at 55."
    2) Might be your least wacko hypothesis. Severely retarted timing for emissions reasons is one of the main reasons circa 1974 engines were so inefficient. (My '72 Subaru, for example, had a device to retard timing at light loads, instead of advance it, as was conventional.) I wouldn't expect Toyota to have to resort to that strategy on a modern engine.
    3) How could they burn a super-rich mixture without adverse effects on catalytic converters, or high emissions? Knock shouldn't be an issue at such a light load.
    4) Fuel rate at 50 mph and ~32 mpg would be nearly 6 liters/hour, well within normal range of air and fuel metering for that engine.
    5?) Maybe something funny going on with EGR (or lack thereof) at that speed? Wayne's subsequent comments seem to rule out obvious transmission-related theories.

    PS I agree. It does have the disadvantage of failing to account for the effects of weight on fuel consumption during acceleration or climbing, so we still need the EPA city test or some other weight-sensitive test.
    Last edited: Oct 18, 2015
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  9. phoebeisis

    phoebeisis Well-Known Member

    PS- On further review-
    maybe the retarded ignition timing and/or richer mixture
    have more to do with "lugging inhibition" or even NHV at those low low RPMs
    than suppressing a knock problem.
    Could be both of course-
    Poorer FE at a lower speed--is peculiar
    1370 RPMS top gear 50 mph-4 cylinder-normal flywheel effect-roughly V-8 RPMs from 8 years ago

    1370 rpms 4 cylinder 3200 lbs-top gear 50 mph-right on the EDGE of lugging
    I wonder if retarding the ignition has "something" to do with decreasing the tendency to lug??
    And if you retard the ignition-maybe you can't get away with an "on the edge of lean" mixture

    Has anyone here recorded a similar result-modern car?
    Wayne-that car doesn't have a "close off radiator" flap does it?? Not that that could make such a big difference?
    Doesn't the Ran 3.6-maybe some other pickup-have some sort of change of HEIGHT feature??
    I haven't completely given up on that one.
    The Ram-maybe it just lowers itself to allow easy loading of "stuff" and humans
    But on the fly lowering-seems to be too good an idea to ignore(guessing too expensive-too little improvement in MPG)

    Anyway-this is such a peculiar result
    And it is EXACTLY what Redy "jokingly" mentioned "my F-150 better mpg at 75 than 55mph"
    I have read this-truck forums-many times- they were mistaken of course
    but for some reason Toyota engineers lock this transmission up in 6th gear-when judging from what happens with more revs-at 55 mpg- there was no obvious MPG advantage

    Hey-why don't USA corps-use the "robot shifting automatic manual" transmissions like the pricy Euro brands?? Too expensive-too heavy-too jerky?? Nice solid lockup-all gears?

    Obviously-no job today-fed cats/dog-waiting for my body to be loose enough to ride my bike-so thinking out loud-

    But all is well with the world
    1)Saints beat Atlanta
    2)ND beat USC
    3)LSU beat Florida
    4)Seattle lost-always a good thing

    One sour note-Alabama-Alabama sucks- won-
    Last edited: Oct 19, 2015
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  10. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi All:

    Just completed the 2016 Scion iA Speed vs FE graph.

    Temps from 54 to 56 degreees with winds out of the North at about 10 mph.


    aFCD Offset = 0.984
    EPA Highway Crossover at 68.6 mph
    RPM@60 mph = 1,950 RPM
    OEM Speedometer vs. Garmin: 60 mph at 60 mph actual and 70 mph at 69 mph actual.

    I am not so confident in the 70 mph results as it was 04:30 am and there was more NB traffic than I would normally experience.

  11. hunter44102

    hunter44102 Well-Known Member

    Would love to see the new 2016 Accord 2.4/CVT, and the new 2016 Civic 1.5/CVT. They have both had improvments over the last gen's, with lighter materials and aerodynamic improvments
    xcel likes this.
  12. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Hunter44102:

    The 16 Accord CVT is on the list as is all three Civic drivetrains. Let us hope we can catch a few sometime this year or early next.

  13. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi All:

    2016 Chevrolet Silverado 2500 HD 4X4 - Speed vs FE


    From the graph, a 68 to 70 mph crossover occurs at ~ 19.6 to 19.2 mpg so 19 mpg would more than likely be its highway rating "if it were EPA highway rated."

    RPM@60 mph = 1,480 RPM

    Speedometer at 60 mph actual (Garmin) = 61 mph. CC was at 60 as well. At 70 mph actual (Garmin), the CC and Speedometer are both set and read 71 mph.

    The above was completed in temps from 52 to 54 degrees F with winds of 5 to 10 mph out of the West on the North/South Runs.

    Last edited: Nov 8, 2015
  14. phoebeisis

    phoebeisis Well-Known Member

    This is a true 3/4 or 1 ton??

    These results are a bit less than the Cummins RAM-which I think got 24 mpg
    but pretty close
    Never thought I would see a 25 mph-hy- 1/2 ton
    and sure as heck not HUGE TD pickups getting better than 20 mpg at actual-65mph- hy speeds
    And an actual 40 mpg 1/2 ton-Italian Ram
    Yeah who would have thought

    Wayne-any chance the poor Ford 2.7 turbo pickup will get a do over??
    Its numbers- were worse than this HUGE truck-
    must have been an aberration
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  15. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Charlie:

    This is the 3/4 Ton.

    I used the F-150 results as a template when building the Silverado HDs Steady State graph above. At each speed, the Chevrolet HD Pickup bested that F-150 with the 2.7L EB but as we both know, the extreme cold weather caused some of that strange low result for the Ford. I almost do not want to go through that 5-hour top off ordeal with the F-150 again either. That was completely unsatisfactory and a total waste of my time. :(

  16. phoebeisis

    phoebeisis Well-Known Member

    One of those weird gas tanks-a bit like the prius I guess
    Yeah it will be obvious-from ford forum members whining very loudly
    if the 2.7 doesn't deliver.
    Those TDs are amazing-all the TD pickups light duty trucks-
    deliver FE and work-tow- capability
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  17. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi All:

    Some very interesting results between the short geared MT and the tall geared CVT…


    For the MT, the Speed vs Fuel Economy graph shows the 34 mpg highway crossover occurred at around 71.55 mpg. This is a little high for a 34 mpg highway Compact CUV so its EPA highway results should be closer to 35 mpg.

    At 60 mph the speedometer matched 60 mph on the Garmin GPS.

    For the CVT, the Speed vs Fuel Economy graph shows the 35 mpg highway crossover occurred at around 67.05 mpg. This is a little low for a 35 mpg highway Compact CUV so its EPA highway results should be closer to 34 mpg.

    Both the MT and CVT at 60 mph per the speedometer matched 60 mph on the Garmin GPS.

  18. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    But if they rated the CVT lower than the MT , people would start to question "Why am I paying MORE for LESS MPG ?"
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  19. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi All:

    Here is one we have all been waiting for. The 2016 Toyota Prius II Eco trim Speed vs Fuel Economy. These are the highest results we have ever recorded so Toyota has a hyper efficient fuel saver on their hands!


    From the graph, the 53 mpg highway rating crossover occurs at 67.9 mph so the 53 mpg rating appears solid although with little room on the downside before falling 1.

    RPM@60 mph = 1,200 to 1,900 RPM depending on small shallow ascents or descents.

    Speedometer at all speeds between 50 and 70 mph were one mph over the actual speed as recorded on the Garmin.

    The above was completed in temps from 52 to 57 degrees F with winds of 5 to 10 mph out of the West on the North/South Runs.

    Just prior to the steady states just before midnight at a great hotel in Dana Point Calif.​

    I had to take some leeway estimating the individual runs as the all-new 2016 Prius can glide from 70 mph and under. SoC was therefore not steady with runs seeing 6 to 5 bars from on the Fly reset to on the fly recording. One of the runs began at 4 and ended up at 6-bars so you can imagine the headache this causes... I was completing the calibration drive and the Speed vs FE on two consecutive nights after 20+ hour days. It was not as fun as I had hoped due to the long hours.

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  20. phoebeisis

    phoebeisis Well-Known Member

    64 mpg at 60mph-at least 10 mpg better than my 2006 prius
    56 mpg at 65 mph-a more common HY speed
    over 50 mpg at 70 mph

    The 64mpg at 60 mph-
    What car comes in second??
    another Prius or one of the TDs??
    and in city driving-normal drivers will get 50 mpg probably
    perhaps 65 mpg with a little effort in stop light to stop light?
    xcel likes this.

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