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Old 04-23-2010, 03:53 AM   #1
rlwhit
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A strange number

The other day I towed a TT several hundred miles. It has an empty weight of 5500#. Got the same mileage as I do when towing the Montana. It must be the frontal area and not weight that has the most effect on milage. The numbers were just from the on board computer, not the old fashon way.
 
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Old 04-23-2010, 04:27 AM   #2
H. John Kohl
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Cummings did a study on big rigs and found that rolling weight resistance turns into Air resistance over 55. They said they found that for every mile over 55 you lose 0.1 mpg.
Thanks for posting.
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Old 04-23-2010, 08:26 AM   #3
mtheo
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Dick
I found the same thing last year when I towed my freinds 25' ulta lite TT to the desert, a place that I go to at least twice a year. I got poorer mileage pulling his TT than when I pull my 3000RK. Think it has to do with the way the air flow comes off the truck and hits the front of the TT. Kind of like an air dam.
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Old 04-23-2010, 10:25 AM   #4
skypilot
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Yeap - that frontal area is a giant parachute just holding the air back. As Mark said above, it is the air flow but also the actual frontal area that hurts. The air flow is one of the reasons that the air wings that we see on some trucks don't really work all that well. Our trailers are too far back from the airfoil so the air just 'burbles' back behind the truck and ends up creating a great deal of drag. There is a product that was spoken about here in the forum some time ago called "airtabs" that reduced that burble and supposedly resulted in improved mileage. As memory serves, several members were going to add them to their TV and Montanas, but no one ever reported back. The web site for those is http://www.airtab.com/en/35.html .

One other thing -- resistance squares as MPH increases -- so the faster you go, the more air you have to push out of the way and the more resistant it is to moving. Ideally we'd all be driving 45 to 50 mph, however that is not realistic -- we'd be a traffic accident just waiting to happen as someone comes up behind us!!!
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Old 04-23-2010, 02:07 PM   #5
pbahlin
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Doesn't Montana claim a high tech, special shaped front end that reduces drag? Maybe that is having an effect too.

I wonder how Montanas compare to SOB for air resistance.
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Old 04-23-2010, 02:20 PM   #6
Wild Horse
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When we were looking at rv's, one of those I liked was a tt with a "wedge" front end. I couldn't help but thinking it would improve mileage.

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Old 04-23-2010, 02:42 PM   #7
KathyandDave
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Here's the Cummins analysis John Kohl mentioned. There's a ton of info here on many issues discussed on the MOC! There's a diagram showing the effect of the gap between the TV cab and the trailer which may explain the TT results.
http://www.everytime.cummins.com/ass...Whitepaper.pdf
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