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Old 10-06-2014, 04:23 AM   #1 (permalink)
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What is the optimum speed for highway / Motorway travel?

Hello all,

First time poster long time website reader!

I travel to work on a long highway for about 20 miles and I do 56 mph. As I have read and been told this is the optimum speed for fuel economy. A lot of the lorries (trucks!) go at this speed and they need to drive for fuel economy!

Or is 56 mph not the golden number? Is it 65 mph? I have heard people say that.

I am getting 64 mpg from my Ford Fiesta 1.6 TDCi I am very pleased but of course I would like a higher MPG! I have started turning the engine off and coasting down hills. I live in a very hilly part of england which is great! I have also started block gear changing from third to fifth and also doing 30 mph in top gear. I am sure those two techniques will improve my personal best go 64 mpg!

I mainly do motorway driving for my commute to and from work.

I am also getting about 450 miles out of 3/4's of a tank. I never fill the tank as this adds weight! I am considering only filling half a tank but 3/4 lasts me a week and I hate going to the fuel (gas) station!

I am looking into modding my diesel with a remap and some new low rolling resistance continental Eco Contact 5 tyres. This I am sure will get me over the 70 mpg which is hybrid territory!

I also want to get some moon caps! but I can't find any in the uk. Is it easy to make them?

Thanks for your help!

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Old 10-06-2014, 04:59 AM   #2 (permalink)
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Sounds like a job for http://ecomodder.com/forum/showthrea...you-15182.html!

I have heard 55 MPH many times, although I have not read it in these forums, just that it is better than 60, let alone 65, or eighty. Generally speaking, the slower that you drive, the better, but about a liter of gas an hour just idling. The best way to know for sure is with instrumentation, which can be as simple as an OBD-II dongle and Torque or another app. You can get an idea of this in: http://ecomodder.com/forum/showthrea...0-a-30169.html
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Old 10-06-2014, 05:45 AM   #3 (permalink)
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I do know that the US mpg is different to the mpg in the UK. So my 64 mpg will be different than the US mpg. A gallon of fuel in the uk is 4.5 litres I am not sure what the US conversion is!

I am very happy with my diesel it cost 42 to do 450 miles very good! could and will be better! lol
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Old 10-06-2014, 06:38 AM   #4 (permalink)
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A US gallon is 3.79 liters, so US mpg is considerably lower than a UK mpg.

That said, the charts Xist linked to still will show the exact same trend, regardless of US mpg or UK mpg. Speaking very generally the best mileage is the slowest speed that top gear can be held.
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Old 10-06-2014, 07:57 AM   #5 (permalink)
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Quote:
Originally Posted by mada88 View Post
I am getting 64 mpg from my Ford Fiesta 1.6 TDCi I am very pleased but of course I would like a higher MPG! I have started turning the engine off and coasting down hills. I live in a very hilly part of england which is great!
Be careful you don't kill your turbo by turning the engine off while it's hot. You don't need to turn off your engine on a steep hill anyway as if you leave it in gear the engine won't use any fuel anyway, and you'll save the brakes. If the hill isn't that steep, just put in in neutral. Your car probably uses only 0.6l/hr at idle.
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Old 10-07-2014, 07:37 AM   #6 (permalink)
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Using ScanGage on the Honda Accord V6 I found that 50-55 mph got the best mileage. Previous Honda (1986) seemed to be better at 45 mph. So you got to look at the charts to see where to start your testing. YMMV.
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Old 10-07-2014, 11:23 AM   #7 (permalink)
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The best speed for economy is generally the slowest you can go in top gear. Anything higher than that is compromising to there faster.



There's a thread on here somewhere about speed vs MPG. I think the only notable exception was in a Corolla, which actually delivered its best economy in 4th gear, rather than 5th (?)

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