zmotorsports
Utah
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Joined: 11/29/2007
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When we went to Cortez/Durango and Moab two weeks ago we had my brother-in-law following us and he drives 55 MPH. Every time we tried to speed up a little he just disappeared in the mirror. So I stuck between 55 and 60 with our ISL pulling our Jeep. When we filled up I checked the mileage and we went from 6.62 MPG to 8.69 MPG. This was exactly the 30% increase that Roger was told about by the Monaco engineer. It was nice getting that kind of mileage but I just don't know if I can do that very much to get that kind of mileage. Just me personally but I will stick to around 65-68 MPH. Mike.
Mike & Chrystal (F315002)
2003 Monaco Dynasty/ 26' Haulmark Edge trailer
1996 Jeep Grand Cherokee toad
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texasbaskets
Frisco, TX
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Joined: 10/06/2003
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It is the easiest way to improve mileage.
There's far too much data to support slowing down saves fuel, but when gear ratios are spec'd for higher anticipated speeds, you may be in RPM ranges your rig won't like. You do have to realize too that other factors such as wind direction, driving techniques and terrain have a lot to do with it. If you have a tailwind and it's hilly, run at a speed where your engine is happy and the transmission downshifts less.
I've posted the link many times, but Cummins will tell you that below 55, tires are the biggest contributor, and above that, aerodynamics is. Their data is based on millions of miles, not just one fillup between trips.
If you don't want to slow down, look at your driving technique. It's no secret that some driver techniques between "like" vehicles show a 30% difference in the best and worst economy. Slower starts, easy acceleration, anticipating your stops/starts and not idling a lot all help.
 
Michael, Kay, Hans (our Mini-Schnauzer co-pilot) and Prissy (Hans' Malti-Poo co-pilot)
'05 Coachmen SportsCoach SE 372DS a.k.a. "Mana's Cabana"
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hershey
Albuquerque,(fulltime) NM, USA
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Joined: 06/04/2003
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I've tried 55 mph and my 5 spd Allison just rocks between 4th and 5th with the terrain and the fuel mileage drops considerably. My sweet spot seems to be 60 to 62 mph. 270 hp Cummin's and Allison 5 spd 23,000 mh and 3100 lb toad.
hershey - albuquerque, nm
Someday Finally Got Here
My wife does all the driving - I just get to hold the steering wheel.
Expedition - Suzuki Grand Viagra
NASCAR 20 - - 99
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tsisco
SoCal
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Joined: 09/29/2006
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I find that, not only is there a significant diesel savings backing off from my usual 65-70 to 55-60, I'm a lot less tense and there are fewer white knuckle moments. No semi has passed me at a high rate of speed because we're all in the same boat. I like the fuel savings and the slightly later arrival time is no big deal. I'm sold and stickin' with 60.
Dutch Star DP 4025 w/ 4 slides
370 HP Cummins
6 sp Allison
Spartan chassis
Magellan GPS
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cruzgal
Arklahoma or somewhere warm/cool
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Joined: 06/20/2006
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We've found that 62 on the interstates gives us the best mileage because that seems to be the "sweet spot" for our engine/transmission combo. Since that's the speed many of the major truck lines have theirs governed to, we don't seem to pass or get passed by as many trucks because we're traveling the same speed as more of them. We've also noticed many of the owner-operator trucks on the road have also slowed to that speed--guess they've discovered the fuel savings, too!
"Time passes but memories remain"
Fulltime since Jan. 2004
40' Allegro Zephyr
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Two Jayhawks
lenexa ks
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Joined: 03/17/2003
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Beavis wrote:My experience tells me your plan will fail.
I tried 55 mph but checking the tach told me that I was in 5th gear,
mileage sucks in fifth gear. Check it out.
I know a few folks have already commented that their experience is contrary to yours and mine is also. I need to obtain about 63 mph to catch 6th gear. After that I can slow to 45 mph and stay in 6th. The instant read out on my Silverleaf shows about 13 mpg at that speed.
2002 Safari Zanzibar
CAT C12 455/1550
Allison 4000
Saturn Vue w/ReadyBrake
FMCA# 390819
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uncle t
reno,NV
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Joined: 04/17/2002
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What is your time worth? I guess it depends on your employment/retired status, your financial status, and for some, the size of your ego.
Let's do some math. I just got back from a 1050 mile trip on mostly flat terrain. I religiously stuck to 55 mph as best as I could. My mileage for the first 28,000 miles on my Cummins 330 was almost a perfect 8.0. On this trip it was right at 9.5. A whole lot of semis passed me on the interstate portions of my journey and they may have been doing 60-62 on average.
On a 300 mile day, doing 62 you get there in 4 hrs 50 minutes.
Doing 55 you get there in 5 hrs 27 minutes.
You save 37 minutes doing 62.
If fuel is $5.00 gal, and 62 gets you 8 mpg it costs $187.50 in fuel.
If 55 gets you 9.5 mpg, the fuel costs $157.85.
You save $29.65 and it costs you 37 minutes.
That means your time is worth $48.00 hr.
That works for me.
06 Monaco Knight 40PLQ
08 SATURN VUE
BE PREPARED- NEVER BRING A KNIFE TO A GUNFIGHT.
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kenbert
Long Island,NY
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Joined: 06/11/2007
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Skid Row Joe wrote:I run 60 to 65 on the Interstates and run 55 to 60 on non-freeways. My life is worth more to me than getting rear ended by an eighteen-wheeler running up on me at 65 - 75 mph, while I'm doing a mileage test at 55 mph in the right lane. These slow moving RV people are an accident waiting to happen.
Where did you ever see, hear or read about an accident because some rv was going 55mph in the right lane. Accidents happen from high speed. To believe you are at risk in the right lane doing 55mph is ridiculous.
Ken
95 Georgie boy Encounter 37ft 5.9 cummins DP
Saturn SC2
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Gale Hawkins
Murray, KY
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Joined: 07/22/2007
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uncle t your math does work in your rig's case and also running 7 miles slower is a plus when the bad stuff hits the fan.
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Ivylog
Blairsville, Ga. USA
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Joined: 06/30/2004
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Zmotorsport said "we went from 6.62 MPG to 8.69 MPG. This was exactly the 30% increase" Not sure I'd base this on one fill up as my Dynasty will take an extra 20 gallons if it is not level side to side. I often lean it to the right so I can put an extra 20 gallons in it when traveling. It's bad about burping if I lean it to the left. I've found that reducing my speed from 70mph to 60 will increase my mileage from 7 to 8. Did a test on a lonely road in WY and got 10MPG at 45mph over 100 miles. Could not wait to get up to speed as I did not want to take an extra day to get home.
04 Monaco Dynasty 42' quad slide
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