What's seen as the optimal highway speed..? - Fuelly Forums
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Old 02-24-2008, 03:38 AM   #1
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What's seen as the optimal highway speed..?

Last weekend I went to visit my parents, and the bad visibility made the whole 1 lane highway going pretty slow, I'm taking between 70-90 KM/H most of the time. I had to drive in 4th gear often too as my car just bogs in 5th at 2000 rpm (a bogging car with AWD will shake the entire car).

I drove like that for 135 KM and I had just tanked before the trip, and tanked at my "pit stop", and re-filled it...to my suprised I had reached 32 MPG...! That's 5 MPG over my EPA rating for highway (it's in my gaslog). It suprised me as we're still using oxygenated fuel and it was around -5 celcius if I recall.

That really struck me as how speed affect mileage...specialy my car which wants to build boost as the rpm gets higher..!

I know some of you got scangauges, what's the average optimal speed that you get the highest MPG..and at what speed you get the EPA rated MPG.?


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Old 02-24-2008, 05:39 AM   #2
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Your Impreza must be OK in 5th gear at 90km/h. If so, I bet you would do 30+ all the time.

And YES, the speed really affect fuel efficiency! When the gas price is going to be way up, people will start to slow down, maybe, or they just gonna eat less good food, and still drive 120kmh (75mph),

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Old 02-24-2008, 08:18 AM   #3
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I don't agree. People will go as fast as their time is valued.

Gasoline was well below $1.00 about six or seven years ago. Now, it's about four to five times as much, if not more, depending upon the region. I would challenge one to come up with data that shows average speeds have been reduced as a result of the cost of gasoline or even diesel.

Either way, as speed is doubled, the air's affect is squared. Seems as though as one breaks through 60MPH, the consequences are getting bigger more substantially. I don't have data, but I think that was some of the support for the 55MPH speed limit that came out of the manufacturer shortages of the 70's that continued on for quite some time.
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Old 02-24-2008, 08:41 AM   #4
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I will agree with you SD26 that time is a big issue, even though I like saving fuel sometimes when I'm in a hurry or just don't have much spare time I will drive really inefficiently, Over 100km/h, more acceleration and breaking than normally.

At some times if you are paid well for your time it's no use saving one euro in fuel and lose another to dead time in the car.

When I increased speed from 90 to 100km/h the mpg went from 40 to 35mpg but I also had the waterpump and block heater broken and winter instead of summer so it's hard to tell the real difference.

Handy gas mileage and automotive calculators at MilesGallon.com lets you find out the real mpg of your vehicle, calculate the fuel consumption and cost for a trip and how about a tool that gives you the total cost per mile for a specifice vehicle over its lifetime.

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Old 02-24-2008, 09:50 AM   #5
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with the turbocharger, there's a whole additional realm of variables to account for. the turbo will heat the air some, and the IC will cool it off. you'll cool it off more the faster you're moving so you see how the variables add up.
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Old 02-24-2008, 12:03 PM   #6
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around 55-60 is the best for mileage.
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Old 02-24-2008, 03:24 PM   #7
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Originally Posted by Hockey4mnhs View Post
around 55-60 is the best for mileage.
I agree, I've seen the best numbers so far doing this.
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Old 02-24-2008, 05:17 PM   #8
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In my car, I think anything over 50 is excessive. But thats just my gearing and if I did that on the interstate I would get run over. I try to stick to the backroads for just that reason.

And I disagree, I think the educated people on the streets will slow down if we get another unexpected gouging at the pump. I remember like a year ago when we hit a record high in this region, everyone was driving about 50. EVERYONE...
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Old 02-24-2008, 05:30 PM   #9
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I gotta disagree with you on that one. I haven't noticed anyone driving any slower than they did 5 years ago. Think of the national savings in oil dependency if there was a 60mph national speedlimit. Period. No leeway. If you're doing 61, you get a ticket every time. People would ***** and moan for the first year or so, then everyone would get used to it. I bet there's a lot less fatal accidents on the highway also.
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Old 02-24-2008, 05:47 PM   #10
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I only noticed it when we got hit overnight. One day it was $2.89, the next it was $3.17. I think that sudden increase shocked people and thats what made them slow down. Currently, it is more than that, but people are still driving fast. SO, I kinda agree that people arent going to slow down do to price (they get used to it), but those sudden spikes do slow them down.

Wake up tomorrow and gas is 5bucks, there will surely be a difference...

ANd your idea would never work, too many people would make a stink and it wouldnt get passed...

The autobahn with no speedlimit actually has a low accident rate..ironic...

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