My MPG

Discussion in 'Gen 2 Prius Fuel Economy' started by JeremyRay, Jun 12, 2013.

  1. JeremyRay

    JeremyRay New Member

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    - Have you read This Thead Yet?

    Yes, but the link to actually read doesn't work anymore.

    - What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)

    32-36mpg and both.

    - What fuel economy are you expecting and why?

    mid 40s. EPA est

    - What are the approximate outside air temps?

    right now, 100 f

    - How long are your trips?

    anything from 7 minutes to 45 minutes (3 miles - 30 miles). (I haven't gone longer than that yet, but plan to next weekend)

    - How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving?

    So far, majority is city. Avg speed is 45-55 depending on the streets I take. Stop and go, yes, not traffic but stop lights.

    - What region/state are you in? (if you haven't set your location in your profile)

    Southern California, Palm Springs area.

    - What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)

    Mostly flat.

    - Is your oil overfilled? (i.e. above the full mark on the dipstick)

    No, right at the second dot.

    How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here)

    I am not sure how old. I checked the battery now, after 5 hrs of sitting, and it was 12.3 and 11.9 under load.

    Have you had your alignment checked? Any pulling or abnormal tire wear?

    I just got the car a few weeks ago, havent had it check, but no pulling and tire wear is normal.

    - Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).

    No. MSR Rims, Nexen 215/45r17 tires (cheap tires, they were on the car when I got it)

    - What are your tire pressures?

    My pressure reader is out of batteries, so I couldn't check. What should they be at?

    - Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)

    Ford Mustang GT 2004 4.6l 5 speed manual
    13-15mpg depending on how I drove.

    - How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?

    Drive normal besides I have been using cruise control. I do try to stay in electric only just when I pull into my community, its 15 mpg zone and like 200 yards to my house. I break easy and slow.

    - Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?

    No

    - Are you driving using D or B mode?

    D

    - HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?

    AC set at 78 (not auto) with the medium fan setting (its hot out here, ha)

    I know the wheels and tires could drop MPG but I wouldn't imagine it dropping down as far as I am getting. I would like getting in the 40s, im low - mid 30s..
     
  2. SteveLee

    SteveLee Active Member

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    As sensitive as the Prius MPG is to anything outside of its norm, I wouldn't be surprised if these wheels and tires alone made 5-10 mpg difference. I assume they are not low rolling resistance tires, they are 3 sizes wider than stock, increasing drag though the circumference is similar, and the weight of the wheels may be more. Swapping them out with the stock wheels and tires or with those of a friend should provide more information. The battery is not strong but I don't think it would make all of this difference, though it could add to the deficit. Stop and go traffic is not the best driving condition for the Prius mpg but if all other factors were positive it should still get in the low 40's. Sounds like a number of potential issues that could add up to your loss.
     
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  3. Britprius

    Britprius Senior Member

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    I agree with Steve though's tyres and rims are going to be reason for your poor mpg. The UK/EU rating system puts the tyres at an E rating for rolling resistance on a scale of A to G. A being the best this is a poor rating made worse by having 17 inch rims.

    John (Britprius)
     
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  4. JeremyRay

    JeremyRay New Member

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    to be honest I am not a big fan of these wheels anyways (they were on it when I bought it) BUT, I know this is just purely speculation, if I had a LRR tire on those same rims what difference do you think that would make?
     
  5. Rokeby

    Rokeby Member

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    JeremyRay,

    Thanks for filling out the MPG form.

    As previous posters have pointed out, the rims/tires on your car are probably
    having the greatest effect on your MPGs. Easily 5 MPG, possibly 10 MPG.
    That said, your A/C use and lowish 12V battery are also having significant effects.

    The effect of a low 12V battery is not intuitive. Essentially, when the 12V battery is low
    the control algorithms run the DC-to-DC converter continuously to try to charge the
    battery and/or carry to DC loads. If this is happening, the engine will run continuously,
    or nearly so, when the car is stationary, the A/C is off and all the normal 12V loads
    are turned off; lights, radio, fan, etc.

    Your A/C use is understandable, but it's a MPG killer -- and it would be the same in
    any other, make that every other, vehicle as well. I have noted that just the manual
    use of the fan without any temp reduction via A/C also leads to the condition of
    the engine not shutting of when the car is stationary and down go the MPGs.

    Lastly, overiding the control algorithms to move the car 200 yds. using EV mode will
    result in reduced MPGs. Granted, this is non-intuitive. Essentially the car will recharge
    the HV battery and incur a number of conversion losses as energy is converted from
    chemical (gas) to mechanical (turning the motor generator) to electrical going into the
    battery and the same losses in reverse order when you run in EV. Yes, it's a lot of fun,
    but no, it is not very efficient.

    Bottom line: all in all, the MPGs you are seeing do not seem greatly out of line for the
    way your car is set up, the rim/tires, and the way it is being operated.
     
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  6. Britprius

    Britprius Senior Member

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    Work done by F8L has shown even when using LRR tyres on 17 inch rims looses around 5 mpg however your pesent tyres could easily be loosing another 5 mpg.

    John (Britprius)
     
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  7. JeremyRay

    JeremyRay New Member

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    I forgot to mention, I have the touring model which I believe is 195/55-16, instead of the standard 185/65-15, is the 5-10 mpg drop the same for the touring as the standard with the 17" rim?
     
  8. Britprius

    Britprius Senior Member

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    No, I run a UK gen2 Prius and all models come with 16 inch rims as OEM running 195/55/16 tyres although surprisingly going up one size to 205/55/16 has given me better results. This size having lower RR than the 195's.

    I am getting 65 mpg (UK gallons) now the weather has warmed up.

    John (Britprius)
     
  9. dorunron

    dorunron Senior Member

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    Take a look at this string. Another PC forum member experimented with 17" rims and noted a drop in MPG. In the end he went back to stock and his MPG came back.

    Huge loss in fuel economy with wheels | PriusChat

    Also, as Rokeby pointed out above, the A/C usage definitely drags down the MPG. Here in Texas A/C is mandatory during this time of the year. If I run A/C and make it comfortable, I see a good 5 to 10 drop in MPG and sometimes more. If I hypermile with no A/C I can easily get 60 MPG, but if I run the A/C, I have seen low 40's and upper 30's at times. Your A/C usage is correct (78 medium fan speed), but even at that it will still contribute to some loss. Finally, your 12 volt is weak. It is not to the point where it has to be replaced, but it is putting an additional strain on the system which could cause a SMALL amount of loss to MPG.

    Bottom line, between the tires, wheels, A/C, driving styles, and 12 volt status I would say your Prius is operating pretty much normal for those conditions. If you can change the tires to a LRR type, you should see a big difference. If you can go back to the 16" rims, you might see even better MPG. F8L has documented several times where he tried different wheels, and he found that 17" rims did contribute to MPG loss as well as the link above states. I don't recommend you not to use A/C as it is hard on you and hard on the traction battery.

    Good luck to you and I hope this info helps.

    Ron
     
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  10. JeremyRay

    JeremyRay New Member

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    My 5 day forcast has the avg high temp of 103 degrees, so A/C is a must right now. I filled up my tires with some air, they were just a little low, and I noticed a slim mpg difference just in my driving yesterday, which I guess could be a coincidence.
    I don't know how much driving I will put in there, but I will be in San Diego this weekend, mid 70's weather, so I will see how much difference that will make with no A/C.

    I am currently in the process of trading on craigslist my rims for stock rims, had a few people interested but nothing so far.
     
  11. dorunron

    dorunron Senior Member

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    You should see a definite difference with no A/C. If you add hypermiling to the mix the numbers will climb even higher.

    If you do go back to OEM rims, try to wrap them with a good LRR tire. F8L posted a good list for reference. You can access that list from my signature file.

    Good luck to you!

    Ron
     
  12. uart

    uart Senior Member

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    Hi Jeremy. One tip with the prius A/C is that it consumes a lot less power if you don't put the temperature setting too low. Some people like to have their A/C always on full blast, and that's their choice, but I find I can set the temperature fairly high (as high as 77F) and it's still quite comfortable. I think just the fact that it dehumidifies the air makes it a lot more comfortable, even if the air is not freezing cold. This really saves on power an often makes the MPG hit close to negligible for me.
     
  13. JeremyRay

    JeremyRay New Member

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    So.. I really didn't do any driving while in San Diego, maybe 6 miles total once I got there. But I drove this route (basically, give or take 10-15 miles)
    Portola Ave to S Coast Hwy - Google Maps
    which is up and over a mountain and same route on the way back. On the mountain roads I was going anywhere from 45-60mph, on the major freeways 70-75mph, on the smaller freeways 55-60mph. I had to use the A/C on the first 45 minutes there and last 45 minutes back due to the heat. Total on the trip I averaged 45.88mpg for 196 miles (according to manual calculations).
    I am happy with those numbers to be honest with you.

    I do have a question, I found that while coming down part of the mountain in B mode, I pushed the accelerator pedal down but only a little and was gliding, going 60mph.. and then again going about 70mph.. Is the normal to happen? is it bad for the car to glide going that fast in B mode?