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Old 11-15-2020, 08:10 PM   #15
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I've always been of the mindset that lowest RPM in the highest gear gets you the best fuel economy. 1600 sounds about right.
Personally I like not having to turn off my cruise control until I reach my destination.
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Old 11-15-2020, 08:15 PM   #16
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Originally Posted by wolfe10 View Post
For a fact-based look at what affects MPG as well as speed expectations on grades:


https://www.prevostcommunity.com/PDF...%20economy.pdf
Great read, thanks for posting!

Never owned a DP, really interesting to read how they broke all those numbers down.

Always read if fuel economy is #1 goal, under 55MPH is where it’s’s at, some state 53MPH.

You might drop 1 mpg going 10 mph faster? When I had my last coach, gas 38ft, I would try to travel 70-73mph when I could, usually need to draft or have a good tail wind.... lol..... I would get 7.5-8 mpg at 55 mph, sometimes below 6 at 70+ All while pulling a wrangler.

For me being able to travel 50-100 + miles MORE in was worth the drop in fuel economy, it would shorten the drive by several hours in long trips....
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Old 11-15-2020, 08:23 PM   #17
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Great read, thanks for posting!

Never owned a DP, really interesting to read how they broke all those numbers down.

Actually, this applies to all coaches, irrespective of fuel.


Said another way, the "wheel demand HP" to do a job can be from any source.


Ya, some gas engines may be turning 5,000 RPM to do the same job a diesel could do at 2,000, but if it can produce the HP, the resulting speed on grade will be the same. Won't say the same for MPG!
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Old 11-15-2020, 08:37 PM   #18
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65 is the sweet spot with this truck/trailer......gets 14 plus, most of the time in the 17 area.....1600 to 1800 rpm's....and I can get to N Carolina in a reasonable amount of time....
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Old 11-15-2020, 08:53 PM   #19
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What Crasher said!
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Old 11-15-2020, 09:04 PM   #20
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As cheap as fuel is, I wouldn’t let fuel economy dictate my speed. You’d have to drive a whole lot of miles for 2mpg difference to effect your budget. Plus if you’re driving across the country you’re possibly adding an extra night stay somewhere along the way. Do the math.

2 weekends ago On I-10 west of Ozona Tx My 430hp 40’ DP pulling a 7,000# Excursion was averaging a steady 6.9 mpg at 70mph. As an experiment and because I was bored, I bumped the cruise up to 80 and the fuel mileage increased to 7.0 . Speed limit is 80.

I would commit suicide if I had to drive 60 out on that lonely stretch of highway.

I usually let traffic dictate my speed more than anything.
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Old 11-16-2020, 06:49 AM   #21
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I drive at 63 to 66 MPH, depending on traffic speed.

I want to be the slower guy so that the blocks of traffic pass me by, leaving me clear roads.
If you keep up with the flow, your buried in the crowd of erratic drivers fighting to get thru it.

Don't like my ( above the posted minimum ) speed, go around me.
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Old 11-16-2020, 07:18 AM   #22
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Here are some quick numbers to consider:


The mileage from Harrisburg PA to Key West FL is roughly 1300 miles.



If you were able to milk it with a tail wind and get 9 mpg you would burn 144 gallons. If you really flogged it and got it down as low as 6mpg you would burn 432 gallons. Both of these extremes are fairly unlikely and you are more likely only talking about a mile or so difference. Anyhow to illustrate the difference in cost if you were paying $2 per gallon:


6mpg =burned 216 gal = $432 fuel cost
9 mpg =144 gal =$288 fuel cost

The difference in this example is a savings of $144




As I mentioned above, I am doubtful that you could realize a fuel savings this large, but it could be possible. I am all for saving money, but if I were concerned about saving $144 I would stay home.
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Old 11-16-2020, 07:41 AM   #23
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Our RV is a 360HP, we pull an F150 toad (~5600lbs), drive about 65-68MHP on the freeway. On a recent trip to the Keys (on I95 and the TP), running the generator for AC we averaged about 8.2MPG. So far on each tank fill up I am in the 7.8-8.2MPG range.
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Old 11-16-2020, 08:11 AM   #24
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I drive at 63 to 66 MPH, depending on traffic speed.

I want to be the slower guy so that the blocks of traffic pass me by, leaving me clear roads.
If you keep up with the flow, your buried in the crowd of erratic drivers fighting to get thru it.

Don't like my ( above the posted minimum ) speed, go around me.

My Father used to call those groups of aggressive drivers wolf packs lol. In the RV I bump the cruise to just below the speed they are going so they are pulling away from me but not so slow that the next “pack” catches me immediately. In a car I get ahead of them unless they are going more than 10 over the speed limit. Staying out of the “packs” also means you are leaving yourself an escape route should an evasive maneuver be necessary. It’s amazing how many times merging cars try to merge right into the side of my rv/toad. Apparently Merging is a lost art.
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Old 11-16-2020, 08:15 AM   #25
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What DiverBob57 said!

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Old 11-16-2020, 08:16 AM   #26
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My Father used to call those groups of aggressive drivers wolf packs lol. In the RV I bump the cruise to just below the speed they are going so they are pulling away from me but not so slow that the next “pack” catches me immediately. In a car I get ahead of them unless they are going more than 10 over the speed limit. Staying out of the “packs” also means you are leaving yourself an escape route should an evasive maneuver be necessary. It’s amazing how many times merging cars try to merge right into the side of my rv/toad. Apparently Merging is a lost art.
And now days, big rigs are part of the wolf pack.
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Old 11-16-2020, 08:51 AM   #27
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So I’m cruising down I95 from Harrisburg,PA to the Keys, towing my Jeep in my 43 foot motor home with a 475 hp Cummins. I have my cruise control set at 60mph. The tach is reading 1600 rpm. I’m getting passed by other RV,s (and everyone else) like I’m going backwards. I have that setting strictly to conserve fuel. BTW, I haven’t touched my brakes since PA! I’d love to go 70 like everyone else, but how much more fuel would I burn? What is the “sweet spot” with a rig like mine. I think I was passed by a little old lady on her way to church!
Do you have a 5 speed transmission?

At 55 mph I'm running 1,200 rpm's. Generally, I'll run 65 mph at the fastest. The coach weighs in at 55,500 lbs. plus pulling a 4,200 lb. tow vehicle so I just don't see the need to go faster.

Sure, I'll roll up to 70-75 mph rolling down a hill but not often or if I need to pass a truck to get it done quickly.

At 65 mph, going steady on a long interstate, I can get 6.5-6.8 mpg. In CA where the speed limit is 55 mph while towing, I can get 7.0 mpg.

Your rpm's seem high at 60 mph.

Safe travels!
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Old 11-16-2020, 11:07 AM   #28
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So we all buy a Motorhome that cost more than most folks homes then like the other gentleman posted we look for a free place stay and we worry about our fuel mileage.
My feeling is drive how ever fast I feel the conditions allow and do my best to not hold up traffic. Most of the time I drive the speed limit whatever it is up to about 78. My last two coaches seem to like the 75-78mph speed when conditions allow but rarely do I drive under 70 again unless conditions don’t allow for it. If you think about it you drive your coach to a destination and then unhook and run around in your towed, in my case what I put on the back of my trailer. I personally think driving 60 when the speed limit is 70-75 is a bit slow and is as big of hazard as someone driving faster than traffic allows.
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