Trailer weight vs. aerodynamics

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leheath8

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I am considering purchasing a very small travel trailer and cannot find reliable information regarding the relationship between trailer weight vs. aerodynamics on towing. Would one be safer and/or get better gas mileage if one was towing a slightly lighter, but not aerodynamic trailer (eg. typical boxy travel trailer) or a slightly heavier, but much more aerodynamic trailer (eg. teardrop shaped)?

Thanks in advance :)
 
Hello:
Others will follow with good experience.

My experience as well as conversations with others, especial individuals who pull Travel trailers from Indiana west for the manufacture's, against the wind, is that aerodynamics is responsible for DRAG or resistance (MPG performance) more than weight.

 
Mr Bojangles is correct. Drag determines your gas mileage much more than weight. For example, people who tow a 3000 pound car behind a motorhome report their mileage drops about a half a mile per gallon.
 
You're getting some good info. 

The weight of the trailer will effect starting and stopping performance based on the type of tow vehicle, but once the trailer is moving at speed it's the aero drag that will affect overall mileage.  A way to think about it, if you could mount a sheet of plywood to the roof of your car so that the wood was like a sail, the plywood weighs near nothing compared to your car, but that big sail on the roof would cut deep into your mileage.
 
I had two TTs, one a 17' that weighed 3800 lb loaded going down the road and the other a 30' that weighed 7850 both pulled with a Toyota Tundra.

The 17' seemed to pull much easier than the 30' but probably because of the lower weight it was easier to pull up hill. Because of that I thought that I would get much better MPGs with the smaller trailer. I didn't.

I would get, maybe at best, 1 MPG better. I was getting 11 MPGs with the 30' trailer and only getting 11.5 to 12 pulling the 17'. This was pulling them over the same exact roads at 60 to 62 mph. A big surprised to me.

Now I'm interested to see how my new 5th wheel will do.
 
Drag is the main impediment to fuel mileage, but you probably won't see a whole lot of difference in an "aero" design versus a boxier one for a similar size trailer. Maybe 1 mpg. Maybe. That's because the frontal area is huge regardless of how aero the shape is, so there is still major drag. 60 sq ft of frontal area is still 60 sq ft even if the corners are rounded and the roof sloped.  The only way to really beat the frontal area drag is to reduce the height, e.g. with some sort of fold-down trailer, and thus reduce the sq ft of frontal area substantially.

Weight does matter for mpg, but mostly only when accelerating or climbing hills. A larger, heavier trailer has to have larger tires, and the tires carry more weight, both of which increase the rolling resistance of the tire. However, the rolling resistance of a properly inflated tire is small, so a slight increase has only a small effect.
 
Gary,

I'll agree w/in limits, but remember that  coefficient of drag is a direct factor in that calculation ( D = 1/2 pv^2 csubd times area). To put that in context, a flat front gives a csubd of 1.0 while many autos have a csubd of 0.3. They don't put all those fairings on top of trucks for no reason!

I'd also point out that 1 mpg is a 12 -15% improvement, not insignificant.

Ernie

Note that streamlining is almost as important to the back end as the front.
 
I get about 1-2 better mpg with my new 5th wheel than I did with the old one.  The new one is about 3,000 lbs more in weight and about 1 foot taller.  The old one had a square front the new one has an aerodynamic nose cone.  Wind drag is by far the most important with large trailers.  At the end of the day the mileage going up and down hills probably is less than 5% of the days total towing miles.  Plus the down hill run does help offset the up hill run.
 
leheath8 said:
I am considering purchasing a very small travel trailer and cannot find reliable information regarding the relationship between trailer weight vs. aerodynamics on towing. Would one be safer and/or get better gas mileage if one was towing a slightly lighter, but not aerodynamic trailer (eg. typical boxy travel trailer) or a slightly heavier, but much more aerodynamic trailer (eg. teardrop shaped)?

Thanks in advance :)
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I find that, with my Airstream, I am actually able to achieve the fuel economy people post on the internet for their box TTs.
 
Thank you for the very helpful replies. The two trailers I am considering have extremely different front profiles, so I suspect the more aerodynamic one is probably worth the extra cost. One is a teardrop shape (known to be an "aerodynamically ideal" shape, in general) and the other more resembles a square box; I would estimate that the teardrop shape has perhaps one third to half the frontal area of the other trailer. The teardrop weighs slightly more, but I am guessing the vastly better front end shape and the lower side profile would improve gas mileage and reduce effects of cross winds.
 
I like curves, aesthetically.

There's more to aerodynamics than the front profile.  You also want the trailer to sit as low to the ground as possible, avoid higher profile A/C or other rooftop accessories, and curve the side walls to reduce the effect of crosswinds.



 
Many 18 wheelers attach air foils to the roof of their cab to reduce drag and increase gas mileage. So the trailer with the curvier front end should get better mileage than the boxy one.

http://www.nosecone.com/
 
Unless the aero design is actually tested in a wind tunnel, it is difficult to now whether it is really aerodynamic or just pretty curves. And a nice flow over the front can become a fuel-eating suction (vacuum) at the back. Still, I would opt for the less boxy design on general principles - some chance of aero improvement is nearly always better than none!

Basement air and other features that reduce protrusions on the roof are also important. As are lower profiles, which unfortunately also lead to lower ceiling and fewer overhead cabinets. No good deed goes unpunished!
 
... or just slow down and then aerodynamics isn't the big factor any longer.  Speeds above 55 MPH are super critical about aerodynamics where speeds below 55 MPH are more about rolling resistance.

I typically tow at 55-60 MPH and see much better MPG number at 55 MPG vs. 65 MPH. (Last entry in the fuel logs 14.1 MPG).
 
So the two campers I am now considering are a small tent trailer or a T@B teardrop camper. Assuming both are roughly similar in weight, would either be significantly better or worse from an aerodynamics/gas mileage perspective?
 
leheath8 said:
So the two campers I am now considering are a small tent trailer or a T@B teardrop camper. Assuming both are roughly similar in weight, would either be significantly better or worse from an aerodynamics/gas mileage perspective?
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Probably very little difference, but it will depend on whether one trailer you are considering has more exposure to the wind than the other.  As others have said the culprit in mpg loss is mostly associated with aerodynamic drag.  So when evaluating trailers, you might hook each up behind your tow vehicle and observe how much, if any of the trailer sits above and/or to the sides of your vehicle. 
 
I am inclined to believe that the aero design is the most important. Others may have different experiences and there may be differences between brands and styles. There may be variances depending on the driver also.

We have owned 5 RV's since 1960. Each one was an upgrade, including size and weight. Four have been 5th Wheel models. All were enjoyed and we were happy with all of them.

Our present 5th Wheel RV is a 2010 Montana 3750FL, a little over 39 ft long and the heaviest. However,  I notice that it seems to pull much easier than our previous RV's, as I remember them. In fact we get approximately the MPG pulling our Monty as we get when not pulling anything. The weather (wind) and terrain affect the MPG but on our normal trips we get about 15 to 17 MPG pulling or Monty over average.
 
Rancher Will said:
Our present 5th Wheel RV is a 2010 Montana 3750FL, a little over 39 ft long and the heaviest. However,  I notice that it seems to pull much easier than our previous RV's, as I remember them. In fact we get approximately the MPG pulling our Monty as we get when not pulling anything. The weather (wind) and terrain affect the MPG but on our normal trips we get about 15 to 17 MPG pulling or Monty over average.
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Wow....I have not had a chance to pull our 5th wheel any real distance yet but we are getting ready to take it on its maiden voyage next week (800 miles). I hope I can get something even close to what you are getting. So far the best I have been able to get on other trailers I have pulled is 12 mpgs. 15 would be over the top.

Oh BTW....that 3750FL is a really great layout. My wife and I saw one for the first time at the last RV show. We fell in love with the living area. Unfortunately my truck wouldn't handle the weight nor would my pocket book handle the price but maybe someday. Love the trailer.
 
Here's a photo of my old rig:
http://i262.photobucket.com/albums/ii103/cvhoss/IMG_6549102009.jpg

With the UTV on the rack and pulling the 12,000 lb. trailer, averaged 10 mpg.  Without the trailer and only the UTV on the rack sticking up above the truck, averaged 12 mpg.  Empty truck averaged 17.4 mpg.  Seems obvious to me that aerodynamics has much more effect on mileage than weight.

Randy
 
Excellent advice. Driving slower while towing increases safety substantially, reduces tire wear, reduces wear on your vehicle's engine, transmission and differential, and significantly improves fuel mileage. Remember, air resistance increases at the square of the velocity. The sweet spot while towing is between 50 and 55 mph. If you are towing over 60 mph, you are reducing your safety level, and wasting a lot of fuel! Slow down and enjoy the scenery! BTW, the people who say they get the same fuel mileage regardless of the speed driven, either do not know how to calculate fuel mileage, or are lying.

Mopar1973Man said:
... or just slow down and then aerodynamics isn't the big factor any longer.  Speeds above 55 MPH are super critical about aerodynamics where speeds below 55 MPH are more about rolling resistance.

I typically tow at 55-60 MPH and see much better MPG number at 55 MPG vs. 65 MPH. (Last entry in the fuel logs 14.1 MPG).
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