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Highway driving, better MPG with or without cruise control?

Discussion in 'Gen 3 Prius Main Forum' started by Mrpcar, Mar 12, 2013.

  1. Mrpcar

    Mrpcar Active Member

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    I did a search and couldn't find anything useful.

    Does anyone know if using cruise control in the Prius for long trips on the highway will result better MPG vs no cruise control?

    What's the best MPH to cruise at? Never mind the speed limit.
     
  2. css28

    css28 Senior Member

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    Conventional wisdom is that you'll get better mileage avoiding the cruise control if you're encountering hills. Your advantage is that you can see the upcoming hills and (traffic permitting) build up a little speed approaching and let it bleed off as you ascend. I will use cruise control for dead flat terrain.
    Best speed for mpg is probably around 30 mph of you can pulse and glide. On the highway 50 is better than 60 which is better than 70 because of the work pushing the air around.
     
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  3. Mrpcar

    Mrpcar Active Member

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    Thanks, that's what I thought so too, manually attack any incline. And use cruise on flat or downgrades.

    See this What is the Speed limit on the highway in Nevada?

    Looks like 60 is out of the question, probably around 80+ to avoid blocking traffic.
     
  4. tumbleweed

    tumbleweed Senior Member

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    Cruise control off is better for mileage if you pay attention if you don't your better off with CC on. CC is much nicer to other drivers and I usually use it on highways when there is traffic. On open highways with higher speed limits I usually set the CC for 2 or 3 MPH over the speed limit to compensate for speedometer error, that seems to keep me at the same speed as most of the other cars.
     
  5. mjones12

    mjones12 Member

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    On my 80-mile weekday round trip here in the flat part of North Carolina, I set the cruise on 55 (limit is 55 and 60), stay in the right lane and get about 62 mpg in summer (low 50's in winter). A lot of people pass me, but I don't cause a traffic jam.
     
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  6. David Beale

    David Beale Senior Member

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    Best MPG is actually similar to most cars, 45-55 MPH.

    Building up speed for a hill doesn't save fuel. Coasting over the top letting the speed drop as you approach the top is what helps mileage. Cruise doesn't do that.

    Other than that, running on cruise is not noticeably different from using the pedal manually, mileage wise. At least that's what I see.

    The Prius engine is most efficient at about 80% full throttle. So near full throttle is actually good, provided you can then coast for awhile.
     
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  7. Mrpcar

    Mrpcar Active Member

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    thanks for all the input. I will report my MPG after my road trip.
     
  8. F8L

    F8L Protecting Habitat & AG Lands

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    Here is Bob's famous chart. It's fairly accurate given the variable nature of driving conditions.
    Prius mpg vs. speed.jpg

    For me, the difference between driving 80mph (40mpg) vs. 65mph (55mpg) would cost me over $700 annually (30,000 miles / mpg * $3.8). No one else is paying for my fuel so if they don't like me driving the speed limit then F' them. :)
     
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  9. Mrpcar

    Mrpcar Active Member

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    WOW! That's pretty accurate, which explain why we are getting 40 mpg on our Prius as we always drive around 80 mph.
     
  10. F8L

    F8L Protecting Habitat & AG Lands

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    Aye. I've been driving a Prius since 2005 and excluding severe conditions, the graph is pretty accurate. On my long trips to LA I generally try to maintain 80-85mph as much as possible. Average displayed speed is usually in the 70mph range and mpg is around 42mpg or so and that was with great tires. :)

    High speed kills mpg. :(
     
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  11. Mrpcar

    Mrpcar Active Member

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    So looks like going with bigger 17" wheel didn't really impact MPG much. :)
     
  12. F8L

    F8L Protecting Habitat & AG Lands

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    Ohh no. It does. I've tested it over and over again. 3mpg minimum loss unless you are using the OE 17" tires. 6+mpg loss if you are using something more performance oriented. lol
     
  13. Mrpcar

    Mrpcar Active Member

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    Side note, I put 100 miles on the X5M yesterday from 71 to 60 to 10 to 405 to 105 to 91 back to 71. Pretty much a big circle around LA. Mostly traffic all the way (LA traffic sucks), and I averaged 16.1 MPG on the X5, my average speed was around 25 mph... if you look below you will see that's pretty good gas mileage. Which makes sense according to the chart. :)
     
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  14. outhouse

    outhouse Member

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    F8L your 12 prius was clean in person.


    Normally the cruise drops my economy.

    But my best trip from Auburn to Rocklin 10 ish miles downhill I made my best trip at 100mpg with cruise on.
     
  15. -1-

    -1- Don

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    :)I prefer cruise control when doing interstate driving. More so with the Prius. I find it difficult to maintain a constant speed without it. I like, "steady as she goes"...
     
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  16. fuzzy1

    fuzzy1 Senior Member

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    Last month I was able to cross Nevada in my winter gas guzzler without going over 65 mph. When cars overtake at an average rate of just one every five to ten minutes, there is really no pressure to maintain any particular speed. And between speed limiters and fuel prices, most commercial trucks were sticking to similar speeds.

    As the earlier graph shows, Prius' best MPG is at the slowest speed you can otherwise tolerate, down to about 15-20 mph.
     
  17. F8L

    F8L Protecting Habitat & AG Lands

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    Thanks! Makes me sad that it's gone though. Someone is probably cruising it around Auburn now.
     
  18. David Beale

    David Beale Senior Member

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    I don't see better mileage at speeds lower than 60 km/hr (around 40 MPH), rather I see worse mileage. But I've never been able to maintain motion at 50 km/hr for very long due to lights and traffic. I've always thought the reason the mileage I see drops at speeds below 60 km/hr was because of "parasitic losses". Systems running using power but not providing motive power to the wheels.
    I see the best mileage around 70 km/hr, on cruise or not. And good mileage at 80 km/hr even on very wicked mountain roads.

    So I guess I disagree with the posted graph.
     
  19. F8L

    F8L Protecting Habitat & AG Lands

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    I believe it is meant to illustrate steady state mpg over time. During short distance cruising at low speeds <45mph, the engine may cycle on and off. At times this will put you in EV mode and you'll see "infinite mpg" but when the ICE fires back up to recharge the HV battery, your mpg will drop into the 40s or 50s?. Over time, however, your average would be something over 80mpg. While doing my pulse & glide marathon I was able to get 109mpg with a 35mph average speed for 2+hours.
     
  20. mnsweeps

    mnsweeps Member

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    Got 78.1 MPG driving on LA freeway..Half of it was cruising.