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Old 04-29-2008, 09:09 AM   #43
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At 55 I get 15 with the Duramax, at 65 -70 I get 12.5. Noticed people driving a little slower coming out there this weekend. Maybe fuel is get expressive enough.
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Old 04-29-2008, 09:10 AM   #44
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Fuel Economy Factors

Thought I'd add a few thoughts and observations. Before retiring I worked in a field related to the auto industry and had the opportunity to discover that fuel economy is not a simple issue. Aerodynamic resistance goes up with the square of the speed so increasing speeds and headwinds do have a significant effect - especially for something as big and unstreamlined as a truck and trailer. Rolling resistance and mechanical friction is not as effected by speed, I used to consider it a constant for simple calculations. However, tire rolling resistance is a function of weight so all those extra pounds of trailer and truck do add up. It has been a while, but I think that we assumed 8 to 10 pounds of resistance for each 1000 pounds of vehicle mass. (This varies with tire design and temperature. I drove a test vehicle 1200 miles to a test site in August and had to repeat the trip in December - same vehicle, route and drivers using cruise control - about 10 percent lower economy with cooler temperatures.)

Engine efficiency is also complicated. At full power, peak efficiency typically is close to peak torque RPM. However, we don't need full power when cruising. Each engine has a different "map" but lower engine speeds are usually more efficient - run the highest gear you can given other constraints.

Having said all that my fuel log has a lot of variation. But slower speeds tend to correspond to hills and curves with senic drives. My best fuel economy was at 55 mph on flat Indiana expressway 18 mpg with the 75 trade wind. (2003 Chevy 6.6 diesel, 3.73 giving about 1600 rpm.)

Hope this is of interest.

Whit Nash
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Old 04-29-2008, 09:22 AM   #45
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Quote:
Originally Posted by BillTex
Hi Silver (or should I say Hi Ho?),
Whud you just call me?
[/quote]

...Do you have any numbers for towing mpg recently?

Bill[/quote]
No towing milage - for the first time in a year we missed a month without camping
I hope to get some real figures if my axles come in (due yesterday) and the stars align properly...we are looking at a 4300 mile trip out west in the next month or so!
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Old 04-29-2008, 09:32 AM   #46
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Whit,

Great info, thanks. My Wrangler's aerodynamics would have to improve to be as good as a brick, a brick is smooth on the bottom.



I have often wondered, is it better to be in a higher or lower gear when either one would do the job.



I get 10 mpg between COS and Divide CO towing the Minuet but will average 14-15 for the trip loaded towing between 60-65 mph. Most of the trip to Divide is 3 gear of 5, 45 mph and 3500 rpm, fair bit of elevation gain. Next trip out I will run 55 mph when possible and see what difference it makes.
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Old 05-17-2008, 04:48 PM   #47
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One downside of driving slowly I have found is I've been run off the road by semi's twice while driving my B-190 in two years going the speed limit. This was on two lane roads. Once in the Michigan UP, the other time in Nevada.
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Old 05-17-2008, 08:19 PM   #48
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Most mileage efficiency comes down to driving habits. As noted above, wind resistance is non-linear-the faster you go the worse it gets-faster. Secondly, acceleration costs, so take some time to get up to speed and drive "ahead" so you don't squander your hard earned inertia on unnecessary braking. Pare down the unnecessary weight on your rig- it costs more to lift it up hill and to accelerate it.
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Old 05-18-2008, 03:51 PM   #49
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do 50 -55mph.wind resistance increases after this speed.i can suggest turning off the ac,opening the windows,and wearing ear plugs so the wind doesn't give you a headache ,but who's going to do that.....except me.also driving during optimum weather and road conditions with an excellent radio works too.
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Old 05-18-2008, 04:13 PM   #50
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if you want to save gas on the highway, turn the a/c on and close the windows provided you have a/c and it works.
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Old 05-18-2008, 04:20 PM   #51
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Originally Posted by richie rich
do 50 -55mph.wind resistance increases after this speed.i can suggest turning off the ac,opening the windows,and wearing ear plugs so the wind doesn't give you a headache ,but who's going to do that.....except me.also driving during optimum weather and road conditions with an excellent radio works too.
Speed limit = 75 MPH
Temperture = 103 (today)

If the heat doesn't get you the 18 wheelers will...
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Old 05-18-2008, 05:41 PM   #52
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if you want to save gas on the highway, turn the a/c on and close the windows provided you have a/c and it works.
your myth was busted by them two guys on tv.they did the test and ac off,windows open won.my ear plugs and ray jo woks.
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Old 05-18-2008, 06:01 PM   #53
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Yes, isn't interesting that the drag of the atmosphere on the open windows is worse than the drag on the engine when using A/C? Who'da thot?
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Old 05-18-2008, 06:21 PM   #54
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Yes, isn't interesting that the drag of the atmosphere on the open windows is worse than the drag on the engine when using A/C? Who'da thot?
on the contrary.windows open,ac off is less atmospheric drag.lucyand ricky{they changed his name to nicky in the movie)rode top down .they's ray jo woked too.
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Old 05-18-2008, 06:47 PM   #55
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I have AC and a nice quiet ride in the burb. Windows open and radio blasting is just too tedious. 100 miles of that and I need to pull over for the day. The old adage "If it's too loud, you're too old" not withstanding.
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Old 05-18-2008, 06:52 PM   #56
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your myth was busted by them two guys on tv.they did the test and ac off,windows open won.my ear plugs and ray jo woks.
two different vehicles, two different drivers @ 45 mph, they need to go back to school.
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