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Old 08-19-2013, 01:40 AM   #127
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Maybe... Maybe Not?

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I find the biggest impact on my MPG is actually side-winds , not so much my speed. Probably because to counter the wind I need to turn my tires in to it, which causes the front tires to scrub a bit... Aerodynamics would do nothing for this ...
I believe a rounded shape like an Airstream would help with cross winds to some degree. Don't you think?

Instead of modeling Class As after buses, why not after bullet trains, or jet planes?

David
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Old 08-19-2013, 04:25 AM   #128
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I talked to the owner of a 45-ft., 2006 Prevost who's here in Homer, AK, at the moment. Driving from Connecticut, he's been getting 6 to 7 mpg, he said.
A buddy with a Prevost and 600hp Detroit similarly topped 6 to 7, driving with his hair on fire.

With my thirsty C13, using his complete repertoire of drifting, limited use of exhaust brake, uphill speed fade, etc. coupled with my grandmotherly 63 mph cruise, I can barely hit 6.

Two things that seem to inch up my Silver Leaf mileage, which is shown in hundredths of mpg: changing our dolly toad from a Crosstour to a Prius; and adding to the tire manufacturers' specified psi for our axle-end weights.


Great thread!!


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Incidentally, seems Bobio's greatest mpg secret was drafting behind semis... anyone else try that?

David
I'm somewhat curious, have experimented with trailing semi trucks, didn't see a discernible difference. Just how close in trail is needed?
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Old 08-22-2013, 08:49 PM   #129
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Old 08-22-2013, 09:01 PM   #130
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High jake brake rpm's will cut into mpg. My theory anyway?
No fuel is flowing when the exhaust or Jake brake is used. Don't know for sure about the variable vane units but I'm guessing it's the same.
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Old 08-22-2013, 09:48 PM   #131
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I can tell you that if you draft a semi he will be pissed because he has to work harder to push the air in front of him with you hanging off the rear. I also wonder why we are all so worried about fuel mileage in our excessively heavy, big engine motorhomes? IMHO I didn't purchase my C13 525hp CAT to worry about the difference in fuel mileage. I bought it because I wanted to climb any mountain while maintaining a safe speed without overworking the motor and I get what I get. If I was that worried about it, I wouldn't own a Motorhome...... Just saying.....
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Old 08-22-2013, 09:51 PM   #132
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Also, when the throttle is closed while the Jake is on, the injection system is in deceleration enleanment which means that there is no fuel flowing to the engine and the engine is basically a large air compressor. You will get fantastic mileage if you just go down steep hills all the time......
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Old 08-22-2013, 10:27 PM   #133
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In June we made 5050 miles from Houston through the inter-mountain west in our '11 Damon Astoria 40' DP with a Cummins ISB-XT 360 and an Allison MH 3000 towing an '09 Chevy 1/2 ton crew cab and running 65-70 we averaged 8.3 mpg. Also, of note on the return trip battled 30-45 mph head to quartering winds for 2500 miles.
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Old 08-23-2013, 04:34 AM   #134
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I can tell you that if you draft a semi he will be pissed because he has to work harder to push the air in front of him with you hanging off the rear. I also wonder why we are all so worried about fuel mileage in our excessively heavy, big engine motorhomes? IMHO I didn't purchase my C13 525hp CAT to worry about the difference in fuel mileage. I bought it because I wanted to climb any mountain while maintaining a safe speed without overworking the motor and I get what I get. If I was that worried about it, I wouldn't own a Motorhome...... Just saying.....
... and yet you know exactly what kind of fuel mileage your coach nets.

For us, mileage was a very important factor when we were considering whether or not to get a motorhome. The difference between 11mpg and 6 mpg would be the difference between going or not going on certain trips. We could have never afforded our last trip of 6200 miles getting 6mpg. Not everyone has the same income to fuel expense ratio. It's awesome that you have achieved a level of success where you don't have to consider the cost of fuel in your rig, but it's just not that way for some.

We bought a motorhome to spend time together as a family seeing the country... It would be great if our motorhome was newer/bigger/faster/nicer, but I consider it a privilege and a blessing to own a motorhome that we can afford to drive, even though it's old and not really all that nice compared to most of the ones I've seen out there on the road. Everybody has a different lot in life... I work hard for what we have, and I do my best to stretch our dollar as far as possible... and fuel mileage makes a difference to us... just sayin'...

enjoy what you have...

-cheers
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Old 08-23-2013, 05:46 AM   #135
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Piker, Well said! Kudos!
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Old 08-23-2013, 05:51 AM   #136
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I certainly didn't mean to offend....... I am just saying that I bought what I have because I wanted the comforts that came along with it and accepted the lower fuel mileage. I do like your answer and feel blessed that my family and I can own a Motorhome and make the memories that we have. Have a great day....
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Old 08-23-2013, 07:35 AM   #137
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I can tell you that if you draft a semi he will be pissed because he has to work harder to push the air in front of him with you hanging off the rear.
Not so. The air doesn't get magically thicker in front of a truck when another vehicle is behind. What is happening is you are driving in the 'hole' created by the truck so the following vehicle doesn't need to push aside the air. You are actually reducing the truck's drag caused by the lower pressure air behind the truck.
So actually BOTH vehicles see an improvement in fuel economy. The drafting vehicle will see a much better improvement than the drafted vehicle but both will improve some.
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Old 08-23-2013, 08:20 AM   #138
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Not so. The air doesn't get magically thicker in front of a truck when another vehicle is behind. What is happening is you are driving in the 'hole' created by the truck so the following vehicle doesn't need to push aside the air. You are actually reducing the truck's drag caused by the lower pressure air behind the truck.
So actually BOTH vehicles see an improvement in fuel economy. The drafting vehicle will see a much better improvement than the drafted vehicle but both will improve some.
Absolutely. Why do you think that the Nascar boys form those trains? Because it is more aerodynamic for all the cars in a line rather than one car by itself. I think that the truckers just get pissed having someone on their bumper (unless maybe it is another truck). Even though I am not worried about being rear-ended, I still don't like anyone following too close to us.
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Old 08-23-2013, 08:36 AM   #139
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Absolutely. Why do you think that the Nascar boys form those trains? Because it is more aerodynamic for all the cars in a line rather than one car by itself. I think that the truckers just get pissed having someone on their bumper (unless maybe it is another truck). Even though I am not worried about being rear-ended, I still don't like anyone following too close to us.
Fuel mileage and tailgating should never be in the same sentence.

I hate it. Passionately!

A tailgater can remain 1 car length behind me, as long as the driver does not mind that I gradually slow to encourage finding another draftee.
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Old 08-23-2013, 08:45 AM   #140
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... and yet you know exactly what kind of fuel mileage your coach nets.

For us, mileage was a very important factor when we were considering whether or not to get a motorhome. The difference between 11mpg and 6 mpg would be the difference between going or not going on certain trips. We could have never afforded our last trip of 6200 miles getting 6mpg. Not everyone has the same income to fuel expense ratio. It's awesome that you have achieved a level of success where you don't have to consider the cost of fuel in your rig, but it's just not that way for some.

We bought a motorhome to spend time together as a family seeing the country... It would be great if our motorhome was newer/bigger/faster/nicer, but I consider it a privilege and a blessing to own a motorhome that we can afford to drive, even though it's old and not really all that nice compared to most of the ones I've seen out there on the road. Everybody has a different lot in life... I work hard for what we have, and I do my best to stretch our dollar as far as possible... and fuel mileage makes a difference to us... just sayin'...

enjoy what you have...

-cheers
We are retired and have all the funds we are ever going to have. We need to make them last. Packing our own meals, saving on hotels, avoiding kenneling our dog, using electricity at a resort, etc help stretch dollars. Mileage matters beyond 8-9 mpg. We have a450hp cummins and haven't tried mountains yet but doubt we will ride a semis butt. Tailgating makes me nervous. My reflexes are not what they used to be especially with a 43 foot MH under my family.
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