How are you making so many MPGs!?!

Discussion in 'Gen 3 Prius Fuel Economy' started by nullxposur, Jul 4, 2009.

  1. nullxposur

    nullxposur Junior Member

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    This question is not just for Gen3 but for Gen2 as well. I have a Gen3 II and am making 40-42 mpgs. Granted, I had a 2006 Civic before and I was making 26 on the city, 36 or so on the highway.

    On the Civic, I drove like a maniac on the city. On the highway, I'd range between 70, 80, or sometimes 100 when on free range. With the new Pri, I don't drive like a sh!thead, but I don't, by far, hypermile. I do slowish take offs but still get around 60-70 on the city (lots of interstate roads).

    My question is, how are you all making such huge MPGs? I must say, I'm quite please that I'm not driving as bad as before but still not limiting myself and am getting 40-42. That, to me, is impressive. Still, I see others making 60+ and I must just wonder.
     
  2. patsparks

    patsparks An Aussie perspective

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    Button off early, that's it.
    For me it isn't about accelerating slowly, it's about lifting my foot off the accelerator when I know I'm coming to a red light. Avoid the brakes.
    Read the MPG threads on PC for more information.
     
  3. DeadPhish

    DeadPhish Senior Member

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    DO NOT accelerate slowly from a dead stop. Just punch it and go.
    Accelerate normally even quickly and get up to speed at least as fast as any other driver.....then lift off the pedal and coast / glide as much as possible.

    Two other key issues:
    • if you see that you are likely to have to stop up ahead anticipate and let off the pedal entirely and coast up to the stoppage;
    • NEVER, EVER, EVER come to a dead stop, try to time it so that you're always rolling if possible and if safe and legal.
    OK the last suggestion is probably impossible to do but the point is that coming to a dead stop at any time requires a relatively massive amount of energy to overcome the inertia of sitting still. Stop signs and stop lights back to back to back are death on fuel economy.
     
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  4. yogadoc

    yogadoc Junior Member

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  5. bestmapman

    bestmapman 2010 Prius

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    Drive the speed limit. That should put you at or abovr EPA rating.
     
  6. ken1784

    ken1784 SuperMID designer

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    Following is a copy of my post.
    -----
    There are a lot of factors we see low mileage such as...


    • break-in period - We'll need at least 2000 miles to see a normal results, especially with new tires
    • short trips - We'll need an extra warming up fuel other than the driving fuel
    • A/C use - We'll need an extra fuel for the A/C system energy other than the driving fuel
    • hybrid driving skills - We'll see better and better mileage numbers after learning how to drive our Prius
    • highway driving - Above 46 mph, the engine is always spinning, therefore we see low mileage. Also, we see stronger air drag at higher speed
    • too many stop&go - The best one is non stop 25 - 35 mph driving
    • steep hills - A flat or very gentle up/down hills are good
    • cold weather - We'll see lower mileage on cold weather than the warm weather
    • low tire pressure - We have to set the tire pressure at least recommended value, but higher is better

    If you understand these, you have an opportunity to see more than 85 mpg results. :)
    1000miles a tank

    Hope this helps,
    [email protected]
     
  7. bwilson4web

    bwilson4web i3 and Prime

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    Another approach is to map out the vehicle performance, to look for any "knee in the curve" and "local peaks" (either minimum or maximum.) Once the vehicle performance is known, then drive on the side that favors your price-performance ratio.

    STEADY STATE CRUISE PERFORMANCE

    For my ZVW30:
    [​IMG]
    This chart is not complete, I still have to map the 25-50 mph region with more precision but it gives good planning numbers for cross-country driving.

    HILL CLIMB STEADY SPEED

    Many roads are not level so it is important to understand what speeds impact climb performance:
    [​IMG]
    Now this chart also shows the impact of fuel quality. The lower curve shows that a higher octane but lower energy gasoline reduces MPG but at the peak power production range, the higher octane fuel continues to produce power. The lower octane fuel requires the engine to 'detune' to avoid knock. But at any lower power setting, the higher energy, lower octane fuel is the way to go.

    The other important part is to note that higher climb speeds above 80 mph on a 6% grade requires drawing traction battery power. This is important because it puts the vehicle in a performance range that is not good for the traction battery health. The reason is charge and discharge cycles 'heat pump' the battery modules. So the greater the charge and discharge cycle, the greater the heat and more stress on the traction battery. This should be avoided if you want to achieve a long, long Prius life.

    DOES THIS WORK?

    When I bought my NHW11, 2003 Prius, I mapped MPG vs mph on the trip back and later, in weekly commuting:
    [​IMG]
    This chart showed that staying under 70 mph, cruising at 65 mph, was a great way to cover long distances without spending a lot of fuel. Of course one also needs to keep any eye out for head and tail winds. Also, it is important not to overfill the engine oil. But there was another, unusual dip at 42 mph.

    The performance dip at 42 mph corresponds to a transition point between hybrid mode, where the traction battery can power the car when the engine is not needed, and 'engine always on' mode. The data suggests that transiting this control point is less efficient than being safely below, -4-5 mph, or above, +4-5 mph. This is a guard band, a speed range to avoid.

    As you might expect, I also have hill climb data:
    [​IMG]
    Notice that there is a peak fuel consumption in the 65-70 mph range. This corresponds to maximum engine performance. Above this speed, the NHW11 sustains speed only by drawing power from the traction battery ... this is a bad thing. But look at 55 mph, an inflection point. It turns out that when on a cross country trip, climbing hills at 55 mph does an excellent job of converting gasoline energy into hill potential energy. This also, by happy accident, corresponds to the climb speed of a heavy, semi-trailer truck in the climb lane ... where I follow at a distance.

    By first mapping the vehicle performance, I've driven 70,000 miles with an average fuel consumption of 52.1 MPG. Best of all, my NHW11 has remained well within the design limits so the traction battery and drive train should last a very long time:
    [​IMG]

    MAXIMUM DISTANCE SPEED

    Although interesting, detailed modeling (thanks to [email protected] sharing the NHW11 drag formula) and testing, we've verified the maximum distance speed is 18-20 mph:
    [​IMG]

    A chart is nice but it needs to be verified in the field:
    [​IMG]

    Now there are other, obscure areas to investigate and some simple optimizations. But having a baseline makes it easier to conduct these experiments and tweak the system:

    • cold weather tricks - block heater, radiator block, thermistor hack
    • transaxle lubrication - using Type WS instead of Type T and more frequent changes
    • engine maintenance
    • tires - low rolling resistance, fully inflated, alignment, larger diameter (more of a shifting of critical speeds)
    The Prius is a great engineering puzzle and continues to offer challenges not yet fully investigated. It really is a fun car to figure out.

    Bob Wilson
     
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  8. nullxposur

    nullxposur Junior Member

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    Whoever posted that chart, it was really interesting when I saw it at the original post. It did make me think about driving the speed limit, but my switch to a hybrid is to limit changing my driving habits to that extreme. I had missed the disappointing MPGs threat. Very interesting!

    As for taking off fast, I noticed the harder I was driving it, the more MPGs I was doing as opposed to when I'd use it on ECO mode. Why do you suggest fast take offs? If the engine requires the most energy to go from 0 to pickup, wouldn't it be a big loss of energy? I understand reducing the time you're stopped though.
     
  9. donee

    donee New Member

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    Hi null...,

    I get good mileage by driving 53 mph on the highway, not 80. And by route selection that gets the car warmed up after a cold start quickly. Multiple long stop lights within 10 minutes of startup is a killer for mileage. Especially, if imediately after those lights your taking that cold engine out on an interstate highway.

    Accelleration rate is tricky. Some kinda instrument is needed to do it right. Possibly the "ECO" monitor in the Gen III Prius is that thing. Super slow accelleration only works well in instances where the goal is not to get going too fast as your just going to be stopping ahead. But, if you have enough clear road ahead to coast down to 15 mph, before the light goes green, an optimum accelleration rate will help a bunch.
     
  10. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    driving techniques and conditions are a make it break it situation. you might only be able to improve slightly from the 40-42 mpg you are getting now, then again, you might be able to get an extra 10 mpg by only implementing a few driving habit changes.

    my SPM, when i drove it, i averaged just under 55 mpg. in Nov 2007, i got my Zenn so SO became primary driver. this dropped the overall average to 52-53 mpg, but the SPM was still the "family" car so i drove it when all three of us were together. so it did the occasional long trip out of town, etc.

    now, i have the 2010. its now the family car. the SPM is basically used for commuting (RT is 11 miles) and its mileage is plummeting. the drive is short (5.5 miles one way) flat and at 35 mph in very heavy traffic. (she works during prime time 8-4.30 mon- fri). so add that, toss in much hotter than normal weather with A/C running most of the time and now her average is going to probably be around 48-49 mph (keep in mind, i could still easily do 52-53 mpg in same conditions so driving styles do make a big difference)

    so use the advice given in the previous posts, they are all ways to inch your mileage up. the biggest thing to remember is keeping your momentum. changing speeds is what hurts you. if you get on the freeway and set cruise control for 65 mph and never have to adjust, you will improve your mileage. PERIOD. but the key is, on the freeway, you are going too fast to put your foot on the brake and the reason is, you cant have your foot on the brake and the gas at the same time. if you want to improve your freeway mileage, NEVER TAKE YOUR FOOT OFF THE GAS. doing so simply is too much of a change in momentum (now keep in mind, to avoid a huge increase in insurance rates, it may be necessary occasionally...but the less you do it, the better your mileage will be)

    now, if you get on the freeway, get the attitude that no one is going to squeeze in between you and the car in front of you, your mileage will not improve (this attitude, btw, might get you to work, 2 minutes sooner) remember, EVERY TIME, you touch your brakes , and it does not matter whether you touch them hard enough to slow down, you are hurting your mileage. sounds weird huh?? try it some time... set your CC, and use the adjustment on the stalk to control your speed. it will change your set speed my 1 mph. if you can manage to not hit anyone or disengage CC (because you are about to hit someone) that only means you have learned to anticipate traffic conditions since you (like most people) will most likely not be able to maintain a constant speed on the freeway due to traffic.

    also, while in town, try this. start tracking how many times your foot touches the brake pedal. track this stat for a week. then try to reduce those touches. when i am on a 4 lane road (i try to take these as much as possible unless there is a less traveled back road i can take to my destination) always be timing the light ahead as early as possible. if you see a red light and 5 or more cars already sitting there, then start to coast. normally you would only spend less time waiting at a standstill, but you were able to regen more charge to the battery which does benefit you in a SMALL way (read this to mean that you dont want to do this on purpose...only do it because you have to).

    but occasionally, what will happen is the light will turn green, the cars will move out just in time for you to come coasting up, now you never came to a stop, never touched your brake pedal...what is the result?? on your trip, you probably increased your mpg for that trip 1-3 mpg depending on the length of the trip...probably increased your total tank mpg by a single tenth...not much i agree, but my tanks take me 2+weeks to burn off....

    that means how many chances to perform a perfect light timing in heavy traffic???

    now remember, only do this if there are multiple lanes of travel in each direction. by doing this, you will have people go flying around you just to cut back in front of you to slam on their brakes to avoid hitting the cars stopped at the light.

    as a GREAT source of entertainment, track these people. in 5 minutes, see how much time they have gained by wasting their gas jockeying for position. after i had done this several times only to see the same vehicle 3 cars ahead 5 lights later... this only reinforced by goal to drive all the way across town without touching my brakes once
     
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  11. JimboPalmer

    JimboPalmer Friend to those who want no friends

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    Time spent cruising = good gas mileage
    Time spent accelerating = bad gas mileage

    To maximize cruising time and minimize acceleration time, you need to accelerate briskly and get it over with.
     
  12. HTMLSpinnr

    HTMLSpinnr Moderator
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    Null, are you letting off the accelerator well ahead of when you need to stop or staying on and relying on the brakes at the end? Drivers who stay on (and consume) gas up to the last possible minute don't have a chance of getting great mileage.
     
  13. DeadPhish

    DeadPhish Senior Member

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    In 'quick' start ups a good amount of energy is used in burning fuel but a good amount of that energy is stored in the battery pack. When you then get 'up to speed' and let off the pedal and coast you are using little or no energy at all.

    OTOH if you try to crawl away from a dead stop you are depleting the battery at first until you reach the point when the ICE kicks in then it has to take over to continue to get you 'up to speed' and it has to replenish the depleted battery. Doing it this way uses more energy.

    As to being at a stop it's not so much how long you come to a rest...it's having to come to a rest, period. That's the problem. As Ken noted above the best results will come on trips where you never have to stop...ever. It's the stopping that causes the problems. It doesn't really matter if it's for a second or a minute.

    Newton's First Law of Motion
     
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  14. a priori

    a priori Canonus Curiosus

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    +1. I think this is a bigger issue than learning to glide (or at least talking about it this way helps more!). Looking ahead and timing are huge issues in saving gasoline. Next: Correct tire pressure (meaning as much as you can take, though not to exceed the posted maximum cold pressure rating).
     
  15. wfolta

    wfolta New Member

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    My simplified summary:

    * Accelerate at least fast enough to put the HSI display bar to the far right of the ECO area, perhaps peeking a bit into the PWR area. That is, accelerate briskly, but not like you're trying to beat the guy next to you so you can get in front of him.

    * Look for opportunities to glide. That is, when you can let off of the gas completely -- until you see the instantaneous MPG hit 100 -- then gently press the accelerator until you have no bar showing: no regen, no ECO.

    * Look at road conditions ahead and be smart about gliding, coasting, braking, and maintaining your speed. Consider cars behind you.

    * Keep the car in ECO mode, and the A/C at 78 (which feels much. much cooler than 78 degrees in your house).

    * Inflate front tires to 40 and rear to 38.

    Following these guidelines (in the summer), I get 50+ MPG in our 2010 Prius III without trying any advanced hypermiling techniques or timing stop lights, etc. I have a mixture of city and interstate (with a mixture of open road, where I go 55-70, and stop-n-go backups) and my commute is about 12 miles each way. The car's breaking in (about 750 miles now) and I'm up to 55 MPG on this tank so far.
     
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  16. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    well, i dont think fast accelerating is a benefit. so you basically want to accelerate fast enough to not be in EV mode, but slow enough that you do not hit power mode on HSI. at least that is what i did to get my last 60+ mpg tank. i usually go up to 25-30 mph at just under the power band, then ease off until i hit the target speed which is either 40 mph. i will accelerate at that rate until around 40 mph if on a 50 mph road.
     
  17. Rybold

    Rybold globally warmed member

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    Indeed. I've noticed other Americans driving around me are also timing the stoplights a lot more again (like they used to when gas was $4.50). Maybe it's also just because people are "taking it easy" during the Fourth of July weekend. But, when I can, I try to not have to come to a complete stop. Sometimes, a stoplight is long and you have no option, but when you can, slow ahead of time and often that light will turn green and you are still going 10mph+. :)
    (think of it this way: if you don't stop, you won't have to accelerate from zero, which in turn saves HUGE amounts of fuel)

    Nullxposur, pretend brake pads are extremely expensive and you are trying to save your brake pads - the more gentle you are with them, the longer they will last. Hard braking "devours" your brake pads. It's okay to use your brakes and "be on the brakes," as long as it is gentle braking. Think of it this way, mentally, and you will see your mpg increase significantly. (what's actually happening here? it will cause you to lift off the gas and begin to brake sooner when you see a red light. and sometimes, that red light will turn green before you get to it. :) )
     
  18. wfolta

    wfolta New Member

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    I think we're saying the same thing, though I allowed that you could peek into the PWR band a bit if traffic called for it. (I am very conscious of not being a jerk to those behind me. I won't trash my mileage because of a guy behind me in a sports car, but I do try to keep up, basically, with the flow.) If you take it to the right side of the ECO area (i.e. just below the PWR area), you'll accelerate fairly briskly, and at the same time get better mileage than if you naively try to accelerate as slowly as possible.

    The naive assumption comes from some hypermiling guides and also from how you might understand the HSI and instantaneous MPG gauges. And also from not fully appreciating what a full hybrid does for you.

    I think the original poster got MPG in the low 40's, so accelerating fast-but-not-furious, etc would probably pull him up to the low 50's without any tricks or inconvenience.
     
  19. nullxposur

    nullxposur Junior Member

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    That's interesting because I'd notice that going "fast" was giving me more MPGs on the digital display than when I was on ECO mode and taking off and driving slowly. So, it seems it's mainly on coasting, maintaining a steady speed and avoiding revving the engine to pass, and using the brakes the least possible as a light form of hypermiling to make use of the most energy and avoid the vast energy needed to take off from a dead stop.

    Thanks folks. I'm sure I knew some of what you all said. I just didn't know tha'ts what you all were doing. I read over the original window sticker and it said city averages between 42 and 52 (or close to that), so I'm at least in the minimum. This next tank gas, we'll see about that! ;-)
     
  20. patsparks

    patsparks An Aussie perspective

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    Please keep us informed.
     
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