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Old 12-14-2012, 09:05 PM   #1
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Surprising Fuel Savings at 55 mph

On our last roadtrip, I miscalculated the distance to our next fuel stop and decided to slow down a little to save gas. (Not as bad as it sounds, since we carry 5+ gallons in a marine tank to refuel our generators, which can be used for emergencies.)

When I slowed from 60 to 55 mph, I reset the computer on our 2008 Tundra CrewMax (5.7L, 2WD) to see if this would help any.

Before resetting the computer, we were getting 12.2 mpg. After slowing to 55 mph, the computer reading at the next gas stop indicated that we had gotten 15.2 mpg over the previous 150 miles (at 55). And, this average held steady over the next 100 miles to our next stopover. I expected a slight improvement, but 3 mpg was a real surprise.

I really don't want to drive slower, but a 24% improvement in fuel economy is making me reconsider our cruising speed. And, that 5 mph didn't seem to make much difference in the traffic passing us.

Is anyone else driving 55 to save fuel?
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Old 12-14-2012, 09:11 PM   #2
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On our last roadtrip, I miscalculated the distance to our next fuel stop and decided to slow down a little to save gas. (Not as bad as it sounds, since we carry 5+ gallons in a marine tank to refuel our generators, which can be used for emergencies.)

When I slowed from 60 to 55 mph, I reset the computer on our 2008 Tundra CrewMax (5.7L, 2WD) to see if this would help any.

Before resetting the computer, we were getting 12.2 mpg. After slowing to 55 mph, the computer reading at the next gas stop indicated that we had gotten 15.2 mpg over the previous 150 miles (at 55). And, this average held steady over the next 100 miles to our next stopover. I expected a slight improvement, but 3 mpg was a real surprise.

I really don't want to drive slower, but a 24% improvement in fuel economy is making me reconsider our cruising speed. And, that 5 mph didn't seem to make much difference in the traffic passing us.

Is anyone else driving 55 to save fuel?
A great addition to a tow vehicle, is an "Air speed indicator".

If it reads higher than the speedo, then slow down, when towing. If it reads lower than the speedo, then you can increase the towing speed.

You will find that it adds additional mileage to what you have already experienced.

Andy
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Old 12-14-2012, 09:19 PM   #3
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It's the wind resistance that does not increase proportionally with increased speed. It becomes a larger and denser wall to push at higher speeds.

I like 60-65 mph but drop down if heading into the wind to save fuel (money).

doug k
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Old 12-14-2012, 09:39 PM   #4
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Driving 55 mph

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... Is anyone else driving 55 to save fuel?
We routinely tow at 55 mph. There is the fuel savings to consider, as well as the safety factors. I feel much more in control at 55 mph, can react to emergencies better, and can slow down or stop in shorter distances. We have never had a tire failure, and I believe that towing at the slower speed is a factor here.
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Old 12-14-2012, 09:47 PM   #5
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Doug is correct. I usually drive 63, but if I have a lot of time, I'll back it off. Usually the rule of thumb for a solo vehicle is 10% improvement by reducing 5 mph.....so, I guess with the additional frontal area, rear suction and weight, your findings don't surprise me too awful much.
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Old 12-14-2012, 09:58 PM   #6
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It gets even better at 45. Like the time I forgot to fill up at McDermitt, NV and coasted into Winnemucca on the last remnants of diesel fumes in my truck and nursing it along at sub 40 mph speeds . But then, wow, it takes forever to get anywhere. That is a major reason I don't visit Ca towing.

Sometimes I go for mileage and sometimes I just want to get where ever it is I am heading. Like from Tucson to the Rim, who cares what the mileage is, just get us out of the freakin oven and into some cooler temps.
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Old 12-15-2012, 12:07 AM   #7
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Surprising Fuel Savings at 55 mph

Fifty-Five miles per hour is my normal cruising speed when towing either my Airstream, Argosy, or car hauler. With this as a known, I set my travel day accordingly and the trip becomes a time to relax and enjoy the changing scenery. I find that with the Suburban, towing the Overlander reduces my fuel economy by 2 MPG over the solo fuel economy cruising at 65 MPH; the Minuet only reduces the fuel economy by 1 MPG when compared to the solo fuel economy cruising at 65 MPH. I rarely travel Interstates while towing as I don't find them conducive to vacationing and relaxing so much of the time, the posted speed limit maxes out at 55 MPH.

Kevin
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Old 12-15-2012, 07:50 AM   #8
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From an undergraduate physics class, there's a change in the nature of aerodynamic drag on a vehicle that occurs around 60 mph. Up to the change, the drag has a linear relationship to speed, above the break point the drag changes to a square relation. Below the breakpoint the drag increases in proportion to speed and above it the drag increases in proportion to the speed squared (goes way up with a little increase in speed). That's exactly why Pres Carter lowered the national speed limit to 55 mph back in the 70's during the oil shortage, because slowing to that speed uses a significantly lower amount of fuel.
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Old 12-15-2012, 08:22 AM   #9
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Thumbs up 55-58

We tow with an 06 8.1 Burb. 15960lb combined wt.

55-58mph steady cruise, 2500mi trip got 11.1-12.2 mpg.

65mph over an 800mi trip, 8.6-9.2mpg.

Small brain conclusion.....55-58.

Bob
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Old 12-15-2012, 08:24 AM   #10
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On our last rally from Valley of Fire to White Sands, NM our caravan needed to travel at 45mph due to posted limits and the fact our wagon master didn't want to lose anyone. Got 22mpg!
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Old 12-15-2012, 09:34 AM   #11
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That's exactly why Pres Carter lowered the national speed limit to 55 mph back in the 70's during the oil shortage, because slowing to that speed uses a significantly lower amount of fuel.
I was still in school when President Nixon signed the double nickel law in 1974. Interesting reading how the mileage savings weren't so good -- many states wouldn't enforce the 55 limit as tightly as they had at higher speeds. So yes, it certainly does come down to actual ground speed.

I'm still mulling over Andy's airspeed indicator. This could get positively Rube Goldbergian...
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Old 12-15-2012, 10:01 AM   #12
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So that is how we got 14.5 mpg traveling 750 miles down to the Great Smokey Mountains np and back on the Blue Ridge Parkway. The BRP speed limit is 45 mph.

Dan
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Old 12-15-2012, 10:07 AM   #13
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We are 17000# combined. I tow between 55-58. Yes it takes forever to get there but we use lots less fuel, feel more in control, and the kids see more...
The faster you drive the bigger the parachute.
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Old 12-15-2012, 10:41 AM   #14
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Is anyone else driving 55 to save fuel?
Not to save fuel, but I've done what you did because we had some time to get to our destination and got the results you mentioned - 15+ mpg! Tundra 5.7L 2WD.

Coming back from Death Valley a few years back when gas prices were almost $7 in DV, I slowed down to 55 on my Goldwing motorcycle and got 56 mpg!
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