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New Prius III not gliding as well as I thought it would...

Discussion in 'Gen III 2010+ Prius Fuel Economy' started by vanbran, Mar 31, 2012.

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  1. vanbran

    vanbran Hmm....

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    My Prius glides less efficiently than I thought it would.

    Some background: Our 2008 Chevy Malibu Hybrid was up on the lease this month, and I knew we wanted to do a Prius. So for the previous 3 or 4 months I've been pouring over the videos and threads about pulse and glide. I was practicing P&G in the Malibu and was getting about 30-ish MPG city, which I thought was pretty decent because it's only rated for 22.

    We got our Prius a few weeks ago, and while I love it, I'm really having trouble with the glide. It just slows down really quickly. I'm honestly a bit disappointed because the Malibu would seem glide a lot easier without losing much speed. I thought the Prius would up the ante because it was a full hybrid and had such a low coeffcient of drag, but I'm really finding the only way I can glide without losing speed quickly is when I'm going down a moderate hill or giving it extra gas.

    I'm gliding by taking my foot off the gas and gently applying pressure to keep the HSI bar out of the regen zone, but little if nothing into the EV zone. I don't think I'm doing that part wrong because the Malibu had VERY aggressive regen, so I'm pretty used to feathering the gas to get to the glide. My MPG is decent so far (around 50 MPG), and I know that it will go up as we break in the engine, but I just really expected a better glide.

    Is losing a Kilometer per second or two normal on a flat stretch while gliding? Will it get better when the engine breaks in over time? Did I just have unrealistic expectations because the Malibu never shuts off the engine and thus was probably helping to push even during its glide? (which I'm not sure if it does or not).
  2. F8L

    F8L Protecting Habitat & AG Lands

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    Gliding in the GenIII is both harder to do and less efficient than in the GeII. By less efficient I mean it will not glide nearly as far. I found myself getting annoyed when I would try to start a glide in my usual spot but lose so much speed that I would have to apply throttle again before reaching my stop.

    New tires roll less efficiently than worn tires. As the tires break in and wear down you will be able to glide further. Give it some time.

    Also keep in mind that at high speeds you will lose speed faster than gliding at low speed because of air resistance. So if you start a glide at 65mph you will lose speed quickly at first but the rate of loss slows down as speed is reduced and wind resistance is decreased. This is when tire pressure becomes most important as low pressure increases rolling resistance. Keep your tires air up properly.
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  3. walter Lee

    walter Lee Hypermiling Padawan

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    From how you've explained it - you have the correct idea down on how to initiate a glide on a Prius.

    * The Prius initially slows down really quickly in a glide during the first 3 to 10 minutes of operation from a cold start. The warmer the outside driving temperature the sooner the Prius will allow a full gliding function. Initially, the Prius gasoline engine will initally stay on to warm up the catalytic converter/emission system until the internal ICE coolant reaches 103 F. Even after that initial warm up period - the Prius needs to be warm up further to extend a glide unless the Prius is rolling downhill. After the gasoline engine coolant is somewhere over 140 degrees Fahrenheit the Prius starts to glide more effortless --- by that time I've normally driven over 15 minutes/4 miles.

    * A Prius glide is also affected by the type of road surface - rough/grooved road surfaces like a rumble strips or grooved roads before asphalt road resurfacing will shorten how long a Prius can glide. A dry newly resurfaced asphalt road tends to provide the best gliding experience.

    * A Prius glide is also affected by tire pressure. Anything lower than Toyota's recommend tire pressure setting (35psi front/ 33 psi rear) listed on the driver's door frame will cause the Prius glides to be shortened. At speeds under 40 mph, dry smooth road surfaces, with no headwinds- overinflating the tires by 7 psi (42psi front/40psi rear) can significantly extend your glides that are under 40mph.

    * A Prius glide is also affected by the road elevation angle. Going downhill extends a glide while going uphill shortens a glide. I have a 1.5 mile hilly downhill section of my commute where I can often glide entirely by starting at 25 mph - strangely this section of road is more round about path to my home and adds about half mile to my commute but because it gently sloping hilly nature and it doesnt have any stop signs or traffic lights I can use a hypermiling technique call DWL and use almost no gasoline or electricity - whereas the more direct 1 mile path requires quite a bit of gasoline going up a hill and dealing with stop lights and traffic.

    * A Prius glide is also affected by the initial velocity before the gliding session starts. Gliding velocities over 40 mph quickly slow down to velocities between 40 mph to 30 mph in almost all driving conditions unless one is going downhill. With a slight downhill advantage a fully warmed up Prius can glide indefinitely around 35 mph and generate electricity at the same time! For example, I have a .2 mile stretch of my morning commute where there is a slight 5 degree downhill drop - with a fully warmed up Prius, I can set the initial gliding velocity of 35 mph - I can let my foot off entirely off the accelerator so that the Prius is regenerating electricity and then the Prius will glide downhill at 35 mph for the entire .2 mile stretch while increasing the state of charge of the HV battery! There is no free lunch - the Prius mileage for this same .2 mile stretch going home (uphill) is about 35 mpg. i.e. with a running start of 33 mph the ICE has to burn about .90 gallons per hour /1344RPM.

    * driving weather can shorten or optimize a glide session. Driving temperatures colder than 60 degrees F can shorten a glide - the colder the driving temperatures the shorter the glide. Warm driving temperatures can extend a glide. Wet road surfaces caused by rain, ice/sleet, or snow will decrease you gliding while dry road surfaces will help optimize your gliding sessions. To keep the engine warm - I block my air intake grill to my radiator and monitor my coolant temperatures..( this is a whole new ball of wax and another topic/thread unto itself)


    HTH

    Walter Lee
    aka "HyperDrive 1" mileage log on cleanmpg.com
    ('skilled' hypermiler, top 100 hybrids)
    2010 Toyota Prius III Blue Ribbon/Dk Grey, oem floormats
    Yokohama Avid S33D (50 psi front, 48 psi rear)
    grill blocking (on and off)
    ScangaugeII (AVG, Soc,GPH,RPM)+(MPG/VLT, FwT, IGN,TPS)
    Odometer=+20600 miles/60.9mpg/avg 17 mph
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  4. vanbran

    vanbran Hmm....

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    Thanks for the info. I haven't checked the tire pressure yet at all, so I might try that. I'm glad to know F8L that the glide isn't like sliding a hot knife through butter, because that's the impression I was kind of getting.

    I'm just finding that on the same roads, in the same conditions, I'm having to keep the throttle open a lot longer than I used to. In the Malibu I used to be able to speed up quickly to about 60 kph (~37 mph) and glide to the speed limit of 50 kph (~30 mph) until the next red light or someone slowed down. In the Prius I have to keep it quite high in the EV range to stop myself from going to 50 in 10 or 15 seconds.

    Can anyone tell me in their warmed-up, broken in Prius (on a flat, dry, windless road) about how fast you typically slow down in a glide from say 60 kph (~40 mph)
  5. walter Lee

    walter Lee Hypermiling Padawan

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    To get the best fuel efficiency out of your Prius you need to avoid using the Prius' electric motors during a pulse(and glide) and when going up hill - that is you need to rely on using the gas engine rather than the Electric motors - Hence, the HSI display should be pass the 1/2 way mark on the HSI display. You want to avoid pushing the electric motors over the 1/4 way mark on the HSI display because they are less efficient when used over that level. The electric motors are most energy efficient at speed lower than 12 mph on a flat surface and between 20mph to 45 mph going downhill to extend glide session. There are tutorials on this on Priuschat.com, Cleanmpg.com, and on youtube.com

    If you have a Engine Block Heater(EBH) then you use can it to pre warm up your Prius (>=45 minutes/trip) for longer trips and your MPG should shoot up like a rocket and your P&G will be effortless. If you live in Canada and don't have an EBH you might consider getting one installed (especially if you have an outside AC plug to run it). An EBH can help you achieve up to 80mpgs on a Prius.
  6. macman408

    macman408 Electron Guidance Counselor

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    This sounds like one of those high school physics problems... "Take an elephant, whose mass can be neglected and whose shape can be estimated as a sphere..."

    I'm pretty sure in my 14,000-ish miles so far, I have yet to find a flat, dry, windless road. Even where it looks totally flat near me, I can look at a topographical map and discover that, indeed, it is slightly sloped.
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  7. SageBrush

    SageBrush Senior Member

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    VanBran, what speeds are you P&G'g at ? If you stay below 45 mph you will save about 2 kw of ICE drag during the glide phase. If you start the glide at speeds over 45 mph the ICE drag will continue until the car slows down to about 42 mph.

    I drive a Lexus CTh , which you can think of as a bit boxier Prius. This is the season of high numbers (warm, but no AC yet ..) so long as wind is not in the way. Today my round trip of 35 odd miles calculated out to 72 mpg on the ScanGauge. I live in foothills, so my trip downtown was 113 mpg, and my trip home 53 mpg.

    BTW, getting 30 mpg out of a car rated 22 mpg by the EPA is quite a feat. Congrats!
    Obviously you are an economical driver, so F8L's advice to check tyre pressures is spot on. I run my sidewall max rated 51 psi Michelin MXM (I think that is the name) tyres at 46/44 psi.
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  8. vanbran

    vanbran Hmm....

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    Haha, of course. I just mean a ballpark "normal road'. Anytime you as a question people always want to come up with a million reasons why they can't possibly answer it because of all the extra factors.

    Anyways, I was driving around today, and had the HSI screen with the energy flow screen on the display audio. Interestingly, I discovered that the point where I was trying to glide before (with almost no green showing in the EV bar) was still showing regen on the energy screen. I had to get a bit more into the EV section before the arrows reversed direction. The glides seemed better after that.

    I did check the tire pressure and they were all at 38 PSI. I know I could go higher, but the dealer definitely did fill them up.
  9. vanbran

    vanbran Hmm....

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    Thanks Sagebrush!

    What I'm basically doing is pulsing up to ~65 kms (40mph) and then gliding from there. I think I've even got into warp stealth above 70 kph (42 mph) a few times when coming off the highway, because even though the EV mode light stays off, my L/100 km gauge disappears (which is the equivalent of the USA model MPG gauge filling up all the way)? That definately has more drag then when I go into a real stealth.
  10. B. Roberts

    B. Roberts Hypah Milah! Ayuh.

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    Just a technicality here, but on some of these posts about tire inflation pressures, I've noted the term "overinflate" or "overinfaltion" used to denote tire inflation above the door sticker recommended inflation pressure level.

    All tires are marked with a maximum tire inflation limit on the sidewalls. This figure can vary by tire type and manufacturer. The Prius Yokohama Avid S33 tires on my Prius have a Maximum "cold" Inflation limit of 44 PSI (cold tire = to ambient air temperature, so at rest, not driven, at least for couple of hours or more) marked on the tire.

    The term overinflation usually refers to tire pressure that exceeds the tire manufacturers recommended Maximum cold tire Inflation that is found the tire sidewall. This "cold" tire pressure maximum should never be exceeded! Ever.

    You may inflate the tire above the car's recommended tire pressure found on the sticker located on Prius driver's door jamb, but never above the tire manufacturer's Maximum Pressure limit that's printed on your tire. Very dangerous. Can and will lead to structural tire failure.

    Please don't confuse these terms, or fail to clarify what you mean, since there may be some readers here that could be new to this kind of tire information and could misinterpret.
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  11. F8L

    F8L Protecting Habitat & AG Lands

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    Please keep in mind that there has been no evidence, in the Prius or hypermiling community, of tire failure caused by inflating a tire above the tire manufacture's cold max PSI rating. So the statement you made above is not true. It should be replaced with the word may otherwise it could be construed as FUD.
  12. massparanoia

    massparanoia Active Member

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    I find it is easier for me to glide when I'm in eco mode. I have heavy/big feet and it lessens the throttle response just enough for me to easily keep it in the "glide" range.
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