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Old 05-19-2016, 03:50 PM
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Impressed with MPG, but speed is huge factor

If you are not in a huge hurry, just set the cruise to 55 instead of 75 and see the difference indicated on the dash mpg.

On perfectly flat highway (lots of that in south FL), I was showing 33mpg, up from 22mpg. The numbers aren't exactly matching reality, but they exactly relate to each other. That is a 50% reduction in fuel consumption for a 27% slowdown.

Next time I go up to Orlando, the turnpike has a few 100-mile stretches of pure flat highway. I'll experiment different speeds and then graph it out from 55 up to 85mph.

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Old 05-19-2016, 03:59 PM
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Re: Impressed with MPG, but speed is huge factor

Yup, they say small increases in speed have significant effects in drag and with an SUV it means a lot to fuel economy.
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Old 05-19-2016, 05:59 PM
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Re: Impressed with MPG, but speed is huge factor

That looks about typical, and occurs on all cars. Here is a site that has averaged and graphed the mpg loss for many cars based on dept of energy studies:
Mpg For Speed - Fuel Efficiency Vs. Speed

And it has a calculator to show how much you could save by driving slower.
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Old 05-19-2016, 06:41 PM
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I think its especially true on thd hemi upto about 65 mph you can return some pretty impressive numbers because the MDS is kicked in a good bit of the time and you are riding on 4 cylinders. Above 75 not much MDS time at all and the mpg starts noticably trailing off.
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Old 05-19-2016, 08:05 PM
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Re: Impressed with MPG, but speed is huge factor

Does anyone know approx what would be the most efficient speed to cruise at for the WK2 Regardless of all the main variables? 55ish?
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Old 05-19-2016, 08:56 PM
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Re: Impressed with MPG, but speed is huge factor

JTS', I get great highway mileage at 65 and no more than 70. I suspect there may be a slight incremental improvement at 55, but that's not practical on the Interstate.
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Old 05-19-2016, 09:24 PM
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Re: Impressed with MPG, but speed is huge factor

Really for a barn door the drag of a GC is not that bad, CdA is about 11.6 (31 sq ft FA, .37 Cd) and makes a smooth transition onto my camping trailer.


Best MPG is usually at the lowest speed you can get into top gear and can stay out of PE.
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Old 05-20-2016, 07:42 AM
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Re: Impressed with MPG, but speed is huge factor

For all the cars I have, I always test their relative fuel efficiency at 60 mph, occasionally also at 70 mph. I've found that around that speed of 60 mph the fuel efficiency is maximized, and beyond 70 mph is drops 2-3 mpgs for every 5 mph above 70.
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Old 05-20-2016, 07:54 AM
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Re: Impressed with MPG, but speed is huge factor

That jives with my unscientific experience, too, f1anatic. 70 seems to be the "magic line" and I pretty much don't cross it outside of occasional passing needs.
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Old 05-20-2016, 08:20 AM
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Re: Impressed with MPG, but speed is huge factor

Heh, here in VA, unless I'm running around town I'm rarely cruising under 70. Speed limits up here are 55 on the main lanes, 65 on the HOT lanes. HOT lanes are usually running closer to 80, main lanes run around 70. Once you get farther south, the speed limit opens up to 70, which means everyone does 75-80, except for the occasional left laner doing 90+. I get around 24mpg when I'm headed south doing between 75-80. 17-18 running around town and back and forth to work. '16 V8.

Doing 55 around here will get you killed lol.
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Old 05-20-2016, 12:44 PM
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Re: Impressed with MPG, but speed is huge factor

Are we all in agreement that the in-dash MPG calculator is fairly accurate?
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Old 05-20-2016, 01:00 PM
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Re: Impressed with MPG, but speed is huge factor

I've noticed here in North Florida (being more hilly than south Florida) that my GC is happiest 60-65 mph as far as mpg goes. However up here being more rural people have a tendency to do 80+ on the highway.
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