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10-01-2007, 02:00 PM
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#1
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Guest
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Speed vs. MPG in Real World
I've taken some fairly long trips and have travelled at different speeds, to compare the effect of speed on fuel economy. I suspect some here may be interested.
All tests were done with a Chevy diesel pickup.
1. No trailer, 80MPH "indicated" (Officer, I'm sure I go much slower than that, I'm sure the speedometer is off...): about 15 MPG
2. Towing 2619 at 70 MPH: about 17 MPG
3. Towing 2619 at 60 MPH: about 20-21 MPG
I haven't tried long distances at 60 or 70 MPH without the trailer, and there's no way I'd tow at 80 MPH, so I don't know what the TM is doing to MPG, but I suspect it's very little. Much more significant is how fast I'm driving the thing. It's nice to have such a fuel efficient trailer (when I tell other Chevy diesel & RV owners that I can get 20+ MPG while *towing* they are shocked - I've heard plenty of things like, "I really like the diesel because I get almost 10 MPG when towing!").
All tests were at about 5000 feet above sea level, about 65-75 degree temperatures.
Some other calculations... Assuming diesel costs about $3/gallon, and a 2000 mile trip with my truck:
At 80 MPH (no trailer): $400 of fuel
At 70 MPH (with trailer): $352 of fuel
At 60 MPH (with trailer): $300 of fuel
Of course it'll take about 25% longer to get there at 60 MPH, assuming no stops - but who doesn't make stops? You're also filling up at least one less time at 60 MPH, which probably eliminates some delay. If you want to get there fast, do what a truck driver friend of mine (who's an independent operator - so he drives 60 MPH in his truck, he likes to make money) says: "To get there quick, you just have to make sure you don't use one control: the left door handle."
That all said, I'm definitely in favor of people stopping when they need to and generally taking it easier. You'll still get there, you'll see more, and you'll be more relaxed. Oh, and save a bunch of money (including money on things like maintenance of the vehicle and tires).
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10-01-2007, 05:18 PM
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#2
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Site Sponsor
Join Date: Jul 2003
Location: MD
Posts: 410
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Quote:
Originally Posted by Texas_Camper
I for one am having difficulty understanding the revelance of the above post....
anyone else?????
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Not me. I like hearing anectodal evidence of the relationship between speed and MPG.
__________________
Tim
2004 2720SL TrailManor, 2 X T105, Trimetric 2030RV, TST TPMS
2003 Tundra Access V8 2X4 w/Tow Pkg
Equal-i-zer 1000, Prodigy, McKesh, UnderCover
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10-01-2007, 09:03 PM
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#3
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Former TM Owner
Join Date: Jul 2002
Location: Greenville, WI
Posts: 517
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Quote:
Originally Posted by Texas_Camper
I for one am having difficulty understanding the revelance of the above post....
anyone else?????
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The gent has discovered a previously unknown phenomenon; namely....speed kills...mpg.
The excitement of the discovery was too much to keep secret.
Even I, yes I, have noticed this phenomenon, but until now had failed to fully comprehend the significance!
Denny_A (TIC )
__________________
2002 2720SL ....
New (old) 2002 Silverado 2500 Duramax Diesel (7/13/07) 2008 Copper Canyon 32' Fifth Wheel TT
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10-02-2007, 08:32 AM
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#4
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Site Team
Join Date: Feb 2003
Location: The mountains of Scottsdale, AZ, and the beaches of Maine
Posts: 10,088
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Now c'mon, guys. We all know that higher speed cuts mpg. The government and the consumer agencies have been telling us that for years. But it is always presented as a general statement, like "the moon is far away". No one ever puts any numbers to it. And as a numbers-oriented guy (an engineer, in other words), I appreciate hearing some documented quantified real-world experience.
Bill
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10-02-2007, 11:52 AM
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#5
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Guest
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And just an additional note on this: Wind drag plays a big part in mpg, especially at higher speeds (50-60 and up). Note that drag from air resistance increases as the SQUARE of the speed -- not a linear function, so that's why mpg is better at lower speeds (up to a point -- engine efficiency plays a part, too, and I suspect best engine efficiency is in the 45-55 mph range, though I have little data to corroborate that, other than experience).
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10-02-2007, 12:29 PM
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#6
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Guest
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This is an interesting thread.
Comparing a trip last month via interstate hwy to CT. @ 65 mph, and an recent trip via 2 & 4 lane "55 mph" roads to Harpers Ferry WVa., I think that my truck worked much less this time, even with steeper hills. It just seemed to glide along with no effort, and much less downshifting, albeit I did run with OD off for part of both trips in the hillier (sp) areas. I had already contributed the more relaxed mechanical effort to less wind resistance. Just imagine if you had to push all of the air that a larger RV does.
Chap
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10-02-2007, 01:55 PM
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#7
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Guest
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Engine characteristics, perhaps, also play a role.
I remember many years ago driving my brothers 1968 GTO, with automatic transmission. On flat ground it would idle at 35 mph. Anywhere with a posted speed limit of 30 mph or less required that you ride the brakes.
My TV is way more truck than I need for the TM. If I just gently rest my foot on the gas pedal I will be going 65mph. I have to hold my toes up to drive slower than that. This is very tiring on my leg, so I use cruise control as much as possible.
6 liter engines are not very good at low speeds, on flat ground, at sea level.
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10-02-2007, 03:15 PM
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#8
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Guest
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I tow a '05 3023 with an'04 Mercury Mountaineer with the 4.6L V8. Normal highway driving alone I get around 19 mpg @ 70 mph. Pulling the TM with my wife, 2 kids and all our gear, I get 13-14 mpg @65 mph (around 1,800 rpm) in the midwest with limited hills. This past summer we travelled from the Detroit area to Cape Cod and my overall MPG came in around 11.8.
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10-02-2007, 08:01 PM
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#9
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Guest
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Interesting anecdotes. My Sequoia towing a 3124KS also has the "sweet spot" at just about 60 mph. It's about 19-20 based on instantaneous mileage readouts on the Sequoia, during flat stretches with the cruise nailed at 60 mph.
I figure that unless I'm in a big hurry (which ain't going to happen while towing) I'll try to keep it in that range of 60-65 much of the time. No doubt a long stretch of days out west would tempt me a little higher, but it's good to know where you get the most from your fuel.
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10-03-2007, 05:29 AM
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#10
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TrailManor Master
Join Date: Aug 2004
Location: Ada, OH
Posts: 254
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Has anybody else noticed a substantial increase in milage when following a semi truck?
I have a 2007 Explorer and it has the instant MPG readout. When I follow a semi on Interstate I immediately notice a 2-3 MPG increase if I pull in behind an 18 wheeler. Here in Ohio they are are supposed to go 55 and usually go about 62.
This is with out the TM behind me, but even with the TM I see 1-2 MPG increase when I follow a semi.
I know it is the draft, like you hear them talk about at every race but it still amazes me and even though I don't like following something I will on occasion.
The other thing I notice is that I get a 2-3 MPG change depending on if there is a wind behind me or I am going into the wind. The Explorer is kind of like a box on wheels and the wind makes a big difference.
Keith
__________________
Keith and Kathy
'07 Explorer 4.6 V-8 - '07 2720SL
Equal-i-zer 1000 - Prodigy - McKesh
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