Travel trailer opinions wanted

[slowmover]

Okay let's look at the numbers. What is needed is the FF and the RR GAWR, plus the GCVWR from Toyota (owners manual, door jamb sticker).

First, the trailer

The VISA 19RSD has a dry weight (with zero options, no water, no propane, etc) of 2,832-lbs. It has a CCC of 1,028-lbs for a GVWR of 3,860-lbs.

As the standard 10-15% TW recommendation for American spec trailers is reflected in the TOYOTA 3,500-lb rating, that means they expect a TW of no greater than 525-lbs.

In a recent quote from an engineer (one of a number who like to do this problem solving), "Our members who have reported TV and TT weights, on average, load their TTs to about 85% of the GVWR. And a typical range of values for tongue weight percentage is 12-14%.

85% of GVWR for this trailer is: 3,260-lbs
14% TW is 460-lbs

All looks good, right?

Well, the empty weight of a .32 cd Sienna (stripper, no options, no driver, no fuel) is 4,275-lbs (same as my 1971 big block V8 Chrysler, ha!); and at a rule of thumb for driver, full fuel and options we can add 450-lbs:

4,725-lbs

With wife and two children plus a bit of junk, we can take that, conservatively, to

5,125-lbs.

GVWR is 5,995-lbs
CCC is now at 870-lbs (as distinct from original 1390)

We have added 850-lbs to the van as equipped and loaded. Thus, our Maximum Trailer Weight comes down to 2,650-lbs and the MTW is down to 397-lbs.

The standard answer, the standard analysis is that your trailer is likely a bit much for the van. The loaded-for-camping weight needs to be carefully checked.

The standard answer is that this is how it works on a pickup truck where the WD is 75% on the rear axle (or, about 345-lbs) and 25% to the TT axles (about 115-lbs).

Let's call it The Theory of Squat, the difference between the old and the new, as the "new" involves pickemups and the "old" involves cars.

On a truck the ideal is to have the Steer Axle retain the EXACT same height and weight both empty and hitched.

The way we used to set up WDH in the era pre-1980 when it was with cars we towed was known as the One-Third Rule:

Steer Axle: 1/3 of TW
Drive Axle: 1/3 of TW
Trailer Axles: 1/3 of TW

Or, roughly 2/3 to the car (303-lbs) and 1/3 to the trailer (156-lbs). The 2/3 on the car needs to be divided 50/50 FF/RR (151-lbs per axle), with a discrepancy of 10% or less, the bias preferred to the drive/rear axle.

This is more the way that Andrew Thomson looks to set up tow rigs. It works with low-payload vehicles (not trucks) as the TV re-distributes the weight more efficiently than the 75/25 bias of a truck.

This is roughly said I hope you understand. Thomson's understanding is deep.

You'll want to know the GAWR of each axle, and the empty and loaded weights represented by each from a certified scale. Weigh it with only the driver, full fuel and the stuff that never leaves the van. It will need to be weighed again, loaded for camping. Same for the trailer where empty is represented by full fresh water, propane, and stuff that always stays in trailer (hoses, tools, etc; but not food, etc).

The TW of the trailer is a separate weight that needs to be established.

You'll also want to find out how others are setting up the Sienna for towing (thus the recommendation of Thomson), and get it perfect for your combination.

This takes a stack of scale tickets to accommodate the range of hitch adjustments necessary (from a variety of loadings and trips; just stop off every time for the kids potty break and top off the fuel tank) until you can about guess at it.

Then, you will definitely achieve the best possible fuel mileage as you now have a balanced, well-handling rig where performance is maximized. Disc brakes will allow you to stop the rig faster than the van solo, with no brake fade.

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[slowmover]

Originally Posted by Frank Lee

I don't think any of the trailing edges benefit from radii, nor do the bottom edges but, yes, everything on the leading and top faces besides that rearmost edge.

Crosswinds. Anything that allows wind to pile up against and push is deleterious to all measures of performance.

The wind literally stacks against a non-radiused edge.

A semi, traveling either direction, pushes a bow wave that can easily upset a trailer of non-aero design. It does not hit head-on, and is far longer than the semi itself. The wind is reversing directions many times over a short period on the trailer surfaces.

The bottom is not so important, granted, but ground clearance must be low for this to be in force. A square white box, on beam axles, with the usual high clearance and narrow roll center is nothing more than a target, in a manner of speaking.

As you run the roads note that truckers will inform each other of a slow moving RV, and that as they pass they will move even farther away from it. It would be no trick -- but evil -- to pass at a high rate close up. One shot, one kill . . . .

For the same reason that once crosswinds reach 25 mph or above you will see 5'ers and the boxes pulled over for the day. I've towed in 35-mph constant with gusts to 60 and hardly noticed the trailer as it was the truck that was being pushed.

I have somewhere a quote about radiused edges and trailers. I'll see if I can find it.

[Frank Lee]

Radii don't help on the back.

[miket]

Originally Posted by Frank Lee

Radii don't help on the back.

tell me about it, but diets suck.

[dpero]

I'll reply with my thoughts when I get some time however for now...

Sienna SE Curb weight:
4460 lb.

Cd:
.309

Tires:
235/50R19
Load Index 99 = 1709lbs (775kg) per tire

[slowmover]

Originally Posted by Frank Lee

Radii don't help on the back.

Crosswinds. Period. Trailers don't exist in a wind tunnel. Granted they may not "help" mpg, but any cross-section that will shed sudden hard wind loads is to the better.

Radii are part and parcel of good trailer design. It must get from Point A to Point B un-eventfully.

The trailer rear effectively becomes the front with overtaking big truck traffic.

The economics of big trucks, or of cars, in re fuel economy is not the same as with trailers. The first is restricted by what it does, the second is a relatively small vehicle with a low sail area also featuring a low center of gravity. The ratio of COG and sail area is tiny compared to a trailer. It is also self-powered. The trailer is none of these. Any small penalty is irrelevant by comparison to control of the trailer by the driver. All edges rounded is key in this. Vehicle control trumps all other considerations.

And, as long trailing exits compromise space (teardrop) the interior efficiency is lower and the sail area is raised, incommensurately. A trailer that widens and narrows makes a bit more sense, as does a humped back. but only to a point. Construction costs make them moot for the most part.

But, again, this is a travel trailer where most of it's time and use is stationary. Interior space and overly long length compromised by aerodynamic concerns doesn't make sense at all. It's still a box. But is the box one with melted edges and corners, or sharp ones? Square construction is dirt cheap which is why you see it. There was but a short period where aero played a part in designing travel trailers, and only then in high end rigs.

The quotes below primarily describe commercial equipment, not RV's, and provide some context. The quote I had in mind was more of description than prescription.

Aerodynamics Research Revolutionizes Truck Design

Rounding all four front edges yielded a 52-percent drag reduction, while sealing the bottom of the vehicle gained another 7 percent. The engineers estimated the potential gain in fuel economy to be between 15 and 25 percent at highway speeds.

Rounding the vertical corners on the front and rear of the cab reduced drag by 40 percent while decreasing internal volume by only 1.3 percent. Likewise, rounding the vertical and horizontal corners cut drag by 54 percent, with a 3-percent loss of internal volume.


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Standard semi-trailers have edges rounded with a 20mm radius. Research by DAF has shown that the ideal body or semi-trailer has roundings with a larger radius: the leading edges of the semi-trailer should be rounded with a minimum radius of 150mm, and the side edges with a minimum radius of 60mm.

Container Platform for Aerodynamic Road Transport

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The Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains, Vol. 1*

By Rose McCallen, Fred Browand, James Carl Ross

The aerodynamics of heavy vehicles ... - Google Books

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When designing the truck, the aim is therefore to increase the radius of the corners and to create more rounded shapes, thus avoiding the slipstream effect.

“There is a rule of thumb that says that the radius of the corner should correspond to 10 percent of the width. If we design the truck with these proportions, we will have fulfilled priority number one. Or rather, we will have avoided creating a poor aerodynamic design.”

Volvo Trucks Magazine

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The Aerodynamic Drag of Road Vehicles
Past, Present, and Future
by William H. Bettes

http://calteches.library.caltech.edu/528/2/Bettes.pdf

The back end of a typical 1980 car had fairly well~rounded trailing edges, which, ironically, is the wrong way to go here as opposed to the front end. Rounded trailing edges, by allowing the separation lines to fluctuate, produce a mean wake that is larger than one that would result if you fixed the separating streamlines at the lowest point. If hard edges are properly placed so as to minimize the size of the wake and prevent the fluctuation of the separation lines that occurs with rounded edges, the overall drag of the car would be reduced by about 5 percent.

On a straight truck, one with the van body attached to the cab, rounding the edges of the van with a 10-inch radius makes a difference in drag of almost 3 percent over one with sharp edges. Rounding the vertical edges with a 10-inch radius on a typical trailer pulled by a conventional tractor lowers the drag by almost 17 percent.

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These quotes differ in time. But none address forces other than those encountered in a wind tunnel, and, if so, only tangentially.

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[Frank Lee]

Rounded trailing edges, by allowing the separation lines to fluctuate, produce a mean wake that is larger than one that would result if you fixed the separating streamlines at the lowest point.

Thank you.

[slowmover]

You persist in missing the point Frank Lee? Less than ideal "wake separation" with a 5% penalty is irrelevant with what is important in a travel trailer. Even a tripled penalty is offset by frontal treatment and edge treatment.

Show us the production trailer where squared rear edges match, must less outperform, the acknowledged ideal the past 80-years for all situations to be found on the road concerning winds.



Some other stuff:

A European trailer no longer sold here, but a good design, and pretty good reports from owners in re road manners (Leaks were another thing). The page points out design considerations worth knowing for a travel trailer.

AWARD Travel Trailers
Welcome to Award Recreational Vehicles


An extended discussion in re aero from RV.net. Wes Tausend does a good job, IMO. (The contributors are other trailer owners with a lot of miles).

*>*Wind Drag: V-Nose or Sloped Nose?
Trailer Life Directory Open Roads Forum: Wind Drag: V-Nose or Sloped Nose?


With both the OP's trailer, the BRENDERUP and the AWARD, the front is "V'd" (or splits the air) up & down versus right to left. Is it because of sidewall drag? Or construction/space considerations? Or does it matter?

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[Frank Lee]

Nonna my aero reference material says radii on the BACK are good.

[Christopher Jordan]

What timing! Yesterday an antique dealer told me his hobby was old trailers, and he showed me many old photos (before Airstream). One, which he has, is very thin in front to wide in the middle, then thin in back. Pictures of it new looks like a new design- very streamlined: something I would have thought was about 10 years old. But it was being towed by about a 1934 car. I did not think about that.

He is restoring his and showed me a photo. All stripped. Pre-restore.

"Neat! How old is it?" I asked.
"1936"

Early eco-modding