Help with improving mpg

Discussion in 'Fuel Economy' started by bluemanalbert, Jun 1, 2015.

  1. bluemanalbert

    bluemanalbert just got scangaugED

    Hi, I drive a 2003 elantra MT averaging about 38 mpg with pulse and glide and coasting but I want to improve mpg over the coming summer months. What can I do to improve?

    Sent from my Nexus 4 using RssDemon
  2. Harold

    Harold Well-Known Member

    Good lrr tires is a good start pumped to around 40 lbs. H
  3. The Doctor

    The Doctor Old Dude, New Car

    Without doing any major modifications to my 2013 Kia Soul, 1.6L, I've done just three things to try to maximize my MPG. (and it works great!)

    1. I pumped my tires up to 42 psi, for better handling, performance and better MPG.
    2. I installed a K&N Air Cleaner, for quicker acceleration.
    3. I use Prolong Anti-Friction additive in my oil, which I change every 3k miles, for a smoother and cooler running engine.

    Best MPG I've gotten so far, on a road trip, is 43.9.
    I also use a "Scan Gauge II" so I can monitor my MPG, second by second, for max MPG.

    Only SOME of your MPG is the car.....the rest is the driver.:rolleyes:

    Cheers Mates!
    The Doctor :cool:
  4. waltermlee

    waltermlee Well-Known Member

    Drive in warm temperatures , use low rolling resistance tire, select a route with smooth road surfaces, and drive under 45 mph. plan your route to avoid doing a complete stop (driving without brakes + smart braking + time shifting) ..learn driving with load
  5. timw4mail

    timw4mail Well-Known Member

    Under 45 MPH? Seems like 50-55 is more reasonable, at least in my experience.
  6. some_other_dave

    some_other_dave Well-Known Member

    Not for fuel economy. Your best steady-state cruising FE will come when you are running at the slowest speed you can stand going in your top gear. And it's very rare indeed for engines to be geared so tall that going less than 45MPH will harm them...

  7. Gord

    Gord Super Moderator Staff Member

    ....and all the steady state speed vs fuel economy tests performed by show a direct relationship between slow speed and high mpg - see here
    Check out the graphs.
  8. brick

    brick Answers to "that guy."

    If we're just talking about raw efficiency, that doesn't really apply to newer vehicles with wide-ratio gear boxes that are programmed to keep engine RPMs as low as possible. Manufacturers have also done quite a bit to reduce drive train losses (smaller displacements, low-friction engine internals, torque converters that lock-up at almost any speed, etc.) such that aerodynamics dominate energy usage at lower speeds than they used to.

    But if you're talking about "reasonable" as in safe then you're absolutely right. You won't see me driving 45mph ahead of 70+mph freeway traffic. If I really want to do that I'll plan my routes along secondary roads. A lot of the time that turns out to be a nicer drive and fewer miles, anyway.
  9. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    I have no problem going 55 MPH on the highway when many others are going 70-80. They have two more lanes besides the right lane. Let them go around me or crash into me , I don't care. So far they've always gone around me.

    p.s. the speed limit on this road is 55 MPH.
  10. ksstathead

    ksstathead Moderator

    When doing around 50 or less on a 70/75 interstate, I like to use flashers when oncoming traffic is still well back. Just a couple of flashes wakes up most of them so they can smoothly change lanes. These are lightly travelled highways, as I would not go so slow if impeding others.
  11. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    I rarely travel on roads with a PSL higher than 55 , but when I used to travel Illinois Interstate highways with 65 PSL , I would go 55. Today , those same roads are 70 PSL and who knows how fast traffic is going ? I think I might also use my flashers in that situation.
  12. jcp123

    jcp123 Caliente!

    In the trucks, we are told to flip on the flashers if we can't maintain over 45mph on interstates or other high-speed roads. Big load and a climb means that happens
    More often than you'd think.

    When driving my personal car, I myself keep to about 55-60, anything below 50 and I'll do a courtesy acceleration, at least as far as interstates are concerned. I don't feel that bad as there is the passing lane.
  13. roothorick

    roothorick Active Member

    Wisconsin has been interesting ever since 41 was promoted to interstate status with the corresponding speed limit bump to 70MPH. Most drivers are still not comfortable with it and you're lucky if flow of traffic actually reaches 70.

    Cops here will harass you if going more than 10 under. I probably should cut down to 60, do my part to break traffic jams. But I tend to do 10 over (which has traditionally been flow of traffic cruising speed and outside of 41 still is) out of fear that going slower will result in a significant deviation from Google Maps' expected arrival times and therefore make me late. I should just math out what the 20MPH difference would do to arrival time and leave earlier. At speed limit 70 it's probably not all that big.

    -E- I just done did some math.

    I'm making the following assumptions:

    * I ideally want to go 40MPH
    * The GPS expects me to do 10 over the speed limit
    * Going more than 10 under the speed limit is ill-advised (I stopped doing this because I routinely got pulled over and lectured by police)
    * Therefore, the difference between my actual speed and the GPS-expected speed must be at most 20MPH.

    Here's how the table works out:

    * 40 instead of 45: 112.5% longer
    * 40 instead of 50: 125% longer
    * 40 instead of 55: 137.5% longer
    * 40 instead of 60: 150% longer
    * 45 instead of 65: 144.44...% longer
    * 50 instead of 70: 140% longer
    * 55 instead of 75: 136.3636...% longer
    * 60 instead of 80: 133.33...% longer

    As you'd expect, as the speed difference increases, the trip time increases, linearly, and at a pretty good clip. But once it caps out at 20MPH, something interesting happens. The trip time increase from going slower becomes smaller at what looks like a slightly exponential rate. As you know, the speed to fuel economy ratio has a similar curve. As you get faster and faster, each 5MPH is less and less worth it.

    And of course, these are theoretical worst-case. It will usually be less than this because various factors (mostly traffic, especially on two-lane roads) will prevent you from doing more than the speed limit, which are mostly nonexistent when going under. Also, Google Maps will factor in traffic wherever it has data (which, it will surprise you at times), doubling the hit to speed difference.
    Last edited: Jul 19, 2015
  14. worthywads

    worthywads Don't Feel Like Satan, I am to AAA

    Leaving a little early takes care of arriving late.

    From my experience driving in WI when it was max 65, the majority drove 9-14 (74-79) mph over speed limit, while MN, CO, NE where it was 75 the same people drove 3-6 (78-81)mph over. I imagine overall speed hasn't risen the full 5 mph increase that 70 allows.

    I drive 55-60 in CO with 75 mph speed limit all the time, with no incidence.
  15. roothorick

    roothorick Active Member

    I'm aware. The question becomes HOW early and that's what all that math was about. My conclusion is it's simply not worth it except for trips that will already take 3+ hours, which is state-crossing territory.
  16. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Another factor that favors 55 mpg instead of 45: any kind of elevation changes that would require a downshift. Anything less than top gear will destroy your mileage. Better to be a little faster and keep it in top gear than slower and require a downshift.
  17. roothorick

    roothorick Active Member

    Eh, CC lets you get a lot closer than 55. In my car it's absurdly good at keeping the TC locked and the tranny in the last gear even when right on the edge of the gear on pretty significant grades. And because of the nature of an auto, P&G is, really, not worth it, so you might as well pop CC.

    I gave this a quick and dirty test recently. The vast majority of a ~21 minute trip was on I-41, so I was going 61, except when I found a towtruck going 58ish, which I hung out a ways behind and matched speed. GMaps estimated arrival 15:37; actual arrival 15:42. That's ~114%, so this table is VERY pessimistic.

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