Best Highway Fuel Economy

Discussion in 'Fuel Economy' started by Babsey, Oct 11, 2016.

  1. Babsey

    Babsey Member

    Which cars have the best fuel economy at highway speeds 100km/h (62 mph),
    I'm aware some hybrids and diesel hatches have highway figures arould 3.5lt/100km but some actual results would be appreciated too. I'm interested more in non hybrid cars.

    On a side note best economy at high speeds (>130 kmp/h) would be interesting too.
    I did some driving in italy recently (Hyundai I40 diesel) entirely highway travel,
    returning approx 6.1 lit/100km/h averaging 140km/h.
    Does anyone have any comparison for this?
    xcel likes this.
  2. fishnrib

    fishnrib Christian

    xcel and PaleMelanesian like this.
  3. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    I think Wayne needs a few clones AND give up sleep altogether. :D
    TheFordFamily, kbergene and xcel like this.
  4. Carcus

    Carcus Well-Known Member

    2017 Honda Civic Sedan EX-T 6 speed manual ---that's my guess for the conventional (non-hybrid, non diesel) steady state king.

    /It's probably going to be several months before Wayne can get ahold of one for testing.
    Last edited: Oct 11, 2016
    xcel likes this.
  5. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    For highway steady speed, I'd have to go with the automatic. It runs lower rpm. Once it's locked into top gear (and stays there), gear ratios and rpm make the only difference.

    Of course, nobody drives ONLY on the highway. I'd take the manual every time for its in-town potential.
    TheFordFamily and xcel like this.
  6. Carcus

    Carcus Well-Known Member

    From the other side of the argument,...

    - The EPA highway is the same for both transmissions 42 vs 42. So it's possible the CVT isn't able to make up for it's mechanical efficiency deficit through lower rpm. And (as has been mentioned elsewhere) we've already seen the 6 speed manual best the CVT in steady states on the 2016 HR-V, despite EPA ratings to the contrary. (EPA had the highway ratings: CVT=34, 6MT=33 (updated 2016 ratings), vs Wayne's Steady states at 70 mph: CVT= 33.7, 6MT=34.9)

    Plus, on CVT's I've driven, there is no "locking into top gear",... they just continually wander. So if there's any rolling hills, traffic, changing wind etc... that CVT just keeps walking around,... and I would wonder if it's not just the "less than best" rpm, but the changing rpm that results in inefficiency. (i.e. if that CVT is constantly on the hunt then I think that would be less efficient operation)
    xcel likes this.
  7. seftonm

    seftonm Veteran Staff Member

    I used to think so, but then saw this:

    Maybe there is significantly more frictional loss in the CVT when compared to the manual.
    xcel likes this.
  8. Carcus

    Carcus Well-Known Member

    Another thought on the rpm's:

    It's only a 1.5. So there's not going to be that much fuel flowing through even at the higher (2600-ish) rpm's on the highway. But what you don't want is that turbo stepping in, if the turbo engine is lugged (like at a lower rpm) there's going to be significantly more fuel introduced. So I don't think 500 less highway rpm with the 1.5t would necessarily be a good thing.

    Can all the computers manage the turbo and the CVT into a better "rpm vs boost" combination than a competent 6 speed driver? I dunno. It will take steady states and long term testing to tell ... because I don't trust the OEM's (even Honda) to be completely honest enough to tell me a less expensive transmission is returning better mpg.
    xcel likes this.
  9. ALS

    ALS Super Moderator Staff Member

    I agree with the CVT's, if my Prius had a lock up trans axle I could easily get another three to five mpg on the highway.

    My Volvo 960 2.9L pulls low 29 with its locking torque converter at 65 mpg. I couldn't pull 29 mpg in a stock 2.1L-2.3L Turbo, manual or automatic at 55 mph.
    The Non Turbo 2.3L models all came with locking automatics and 32-33 mpg was easily to do. My brother has a S70 2.5L w/locking torque converter non turbo and all he can pull is 32 mpg highway.

    Right now non hybrid or diesel I would look at the Honda Civic or Nissan Altima for highway mileage.
    xcel likes this.
  10. Carcus

    Carcus Well-Known Member

    "I agree with the CVT's, if my Prius had a lock up trans axle I could easily get another three to five mpg on the highway...."

    But this is a completely different setup than what Honda has in the Civic. Prius = hybrid, planetary gears, port injection, normally aspirated. Civic = "true" CVT, direct injection, turbo charged.
    xcel likes this.
  11. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    The Prius will drastically change the RPM depending upon load. But you can't really make an apples-to-apples comparison of the Prius "transmission" and a regular CVT. And I don't think you would even want the Prius to "lock up". It will find the lowest RPM for that particular load. Just my humble opinion.
    xcel likes this.
  12. Carcus

    Carcus Well-Known Member

    At the risk of being overly optimistic, .. I think it's possible the 1.5t 6mt civic sedan will show a steady state at 70 mph somewhere close to 45 mpg. (65 deg F or warmer).
    xcel likes this.
  13. xcel

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

    Hi All:

    In sedans, the 16 Civic with the 1.5-T and CVT and 17 Elantra SE with the AT. The 17 Elantra Eco may upset that balance. The MT may be a while...

    In CUVs, the Nissan Rogue and Murano with their tall ratioed CVTs would be at the top of my non-hybrid/non-diesel list for highway efficiency.

  14. RedylC94

    RedylC94 Well-Known Member

    If the programming is right, that constant hunting keeps the engine at the speed-torque combination that's most efficient for the level of power demanded, which you can't do with a manual (although you can approximate it if you know what you're doing and work at it). However, that advantage is counteracted in both a mechanical CVT and an "e-CVT" by greater internal losses than a manual has---mostly friction in the mechanical CVT, and electrical losses in the e-CVT.

    A manual would definitely give best steady-state mpg, IF it has a ratio that happens to be near optimum for the conditions. Otherwise, not necessarily so.
    Jay and xcel like this.
  15. BillLin

    BillLin PV solar, geothermal HVAC, hybrids and electrics

    Great topic. You got "everyone" speaking up. :) For me, highway speeds are almost never constant input for constant conditions. The premise behind pulse and glide and the way some hybrids work is to take advantage of the glide portions and not overdoing the pulse. In practice on the highway, there are almost always elevation changes that allow some level of pulse and glide practice without being too obvious. If you "lock" into the steady state mode of a cruise control or a steady foot and constant speeds, you may not fare as well as allowing some natural speed variations.

    Highly discouraged in this discussion group, but I understand your need. For those higher speeds, you may get greater benefits from taller gears and aero modifications.
    xcel likes this.
  16. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Ok, yes. I was thinking of a traditional automatic transmission that does "lock up". CVT is another animal that I have little experience with, so I'll go with the extensive discussion above for that.
    xcel likes this.
  17. Carcus

    Carcus Well-Known Member

    It's worth noting that Honda's CVT does incorporate a torque converter, and in the 1.5t it is an all new "turbine twin-damper design".

    Not that it's relevant to this conversation, but .... you will have computers talking to computers that are managing valve timing, turbo waste gate, fuel control, AND cvt ratio, .AND torque converter ratio ----- all of which have to work together. If you think that an independent shop is going to be able to figure a CVT issue out and get a repair done on the cheap ----- I'd think again.
    BillLin and xcel like this.
  18. Babsey

    Babsey Member

    Thanks for the input, I don't do those speeds where i live (Australia) but it is normal and legal in many countries in europe so I just mentioned it as a point of interest.
    xcel and BillLin like this.
  19. xcel

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

    Hi All:

    I just finished up an 82.1 mile drive in the 17 Elantra Eco with the 1.4L GDI-T.

    A new Sheriff is in town.

  20. all_about_the_glide

    all_about_the_glide Well-Known Member

    How does a 13 PIP stack up: 80% highway miles most likely 20% on the plug.
    Great condition, 27k miles, $15k...about the same $ as a regular Prius.

    My 2007 HCH with a newish bumblebee battery turns into the third car mainly for the 16 year old now with a DL I find living in my house.

Share This Page