Towing Aerodynamics - just for grins

Jimbuffalo2 · Aug 20, 2018

I will be hauling the following with my 2016 TDI:

A VW Tiguan on a UHaul trailer with
(2) 14' kayaks,
(2) bikes (on the Tiguan trailer hitch) and
(1) roof box.

So, for grins (and any air flow engineers out there)….what do you think would be the optimal configuration to reduce drag/turbulence (*whatever)

a) Mount the kayaks on the Touareg with the roof box on the Tiguan?

b) Mount the roof box on the Touareg and the kayaks on the Tiguan?

c) Mount them all on the Tiguan?

d) Mount them all on the Touareg?

All said, I suspect whatever I do won't matter a whole lot, but opinions don't cost much. Anyone understand slipstream? Thoughts?

It's a 2600 mile trip...I'll be real interested to see how the mighty Touareg holds up. A small percentage increase in miles per gallon might pay for my coffee!

Cheers

Patr80l · Aug 20, 2018

More important is the weight distribution.

Jimbuffalo2 · Aug 20, 2018

Yes,,,,the vehicle is about 3400 and trailer about 2000#. I'll spread additional cargo weight between both vehicles. Figure another 300# of bikes and kayaks and roof box another 500# of other stuff.

All in, 6200#.

I suspect no matter where I put stuff, it won't really make a difference, but figure I'd ask. I'm leaning toward putting the kayaks on the Touareg as they are more pointed than the roof box.

Should be a good test

FSJ Guy · Aug 20, 2018

Whatever you do, be sure to take photos and post them here!!!
:- p

buckwheat · Aug 21, 2018

I would put it all on the Touareg, except the bikes. The towed vehicle will sit higher than the tow vehicle, so you are adding to total frontal area by putting things on the roof of the vehicle on a trailer.

I've towed similar set-ups (albeit not with a Touareg), and I shifted the roof gear as much to the rear in an attempt to get it to act as much like a fairing (like on tractor trailers) as possible.

Jimbuffalo2 · Aug 21, 2018

FSJ Guy said:
Whatever you do, be sure to take photos and post them here!!!
:- p

My previous handle Jimbuffalo and I have been on this forum since 2005. Other than the avatar, I still cannot discern how to post pics!!

I'll be sure to take plenty as the kayaks and bikes are for the return trip.

Buckwheat's thoughts make sense...Another thread has convinced me to pack some additional Ad Blue along with my Power Service.

nickyt · Aug 22, 2018

Jimbuffalo2 said:
My previous handle Jimbuffalo and I have been on this forum since 2005.

A good try to deceive us #2, but the truth is more like this...

Make sure the the big guy takes some extra ad blue on the trip and remind him that you are not cargo. You get to ride in the front also, not in the rear compartment. >

Jimbuffalo2 · Sep 12, 2018

Towing Update:

Been pushing the Touareg. Fully loaded.

Chassis is stout, diesel power is great, insofar as concerns about engine braking, etc. -- no issues.

Able to comfortably tow at speeds from 70-74 .....Averaging about 14mpg that way

So here's the deal, something to ponder:

I had the vehicle serviced at 50000...l.o.f, adblue, etc.

Started trip at 52000.

At about 53100, the 600 mile AdBlue warning shows up in Orange. Every 10 miles, it reduced by 50. Hmmmm….I'm in the west end of Nebraska...Denver 300 miles ahead.

I unloaded the trunk and installed the 1/2gal small VW canister I'd brought along.

I then scored another 2.5 gal at a truck stop and added it, cleared the Vehicle Status message - all good - carried on.

Now, 700 miles later, my AdBlue warning comes on in white, saying I have 900 miles.

Hmmm! I drained at least 3 gallons of AdBlue in only 700 miles? Maybe these post-fix cars are not cut out for dragging a load like that.

I just added an additional 2.5gal. Will have a VW shop top me up if I can find one.

Hmmm...seems like something else is happening besides 14mpg based AdBlue consumption and heavy torque application.

Thoughts?

As comparison, post fix I had 8000 miles before a warning message appeared.

buckwheat · Sep 12, 2018

Hmmm. My first thought is that the dealer forgot to fill at 50,000 miles. The one time that I had my dealer fill the ad-blue (for the emissions modification), I had a low DEF warning on my way home, barely 200 miles later. The dealer admitted that they forgot to fill up.

I also had an episode where the estimated range dropped rapidly (not 50 miles every 10, but 200 every 100 miles). After refilling, the level did not reset for about 4 days. I never attempted to reset via VCDS, but I did the 30 seconds of key-on, engine off. Magically, the level reset a couple days before I thought the car was on its way to a no-start condition.

My gut says you cannot consume this much ad-blue, but who knows how the vehicles were reprogrammed. I will be watching for updates. Theoretically, DEF consumption is supposed to be 1 - 2% of fuel consumption, but apparently can be as high as 3%. Worst case, at 3% consumption at 14 mpg, you should be getting 466 mpg of DEF, or approximately 2,100 miles per tank. Your mileage may vary, as they say.

tadpole · Sep 12, 2018

Interesting ,because a poster here said his consumption on his 2016 was lower after the fix. My 2012 would go 10,000 mi without a warning. My new 2016 has 2000 miles on the meter so I'll be following closely because I have a 1500 mi trip coming up,but not towing. My ad blue was topped up now and I will check it when my trip is finished. I will report back.

gazaflash · Sep 12, 2018

JimBuffalo2
Back to the airflow theory...!
The most aerodynamic shape is a aerofoil. Wider at the front and tapers off at the back.
I would go for the roof box on the Touareg, bikes behind the Touareg and kayaks on the trailered Tiguan. Only issue is the space between Touareg and Tiguan is too long!

Xcentric · Sep 12, 2018

I posted this a few months ago in the emissions fix thread:

"I pulled a car hauler 2,500 miles. Sarasota - Fort Worth round trip. Performance differences pre and post fix: zero.

The AdBlue "1,000 miles" left message flashed about 600 miles from home. This was less than 4,000 miles post fix.

Then in about 200 miles, it flashed 650, 500, 350, 150, each with added urgency. "Car will not start."

I bought 2.5 gallons of DEF at a Love's. $15.

Either the dealer did not fill the DEF tank when he did the fix, or DEF consumption is way higher than expected. I suspect the dealer, but we shall see.

Don't count on 1,000 miles to go when the first warning appears. Get a jug of DEF as soon as you can. Five minutes to add."

I haven't pulled a trailer since, but now I'm concerned that towing drastically increases DEF consumption. Pre-fix, the car never needed DEF between oil changes even with extensive towing.

Your 14 mpg is as expected. If you have ST tires on the trailer, at 70-74 mph you are exceeding the speed rating. Slow down to 65 and you'll get 15.5-16 mpg and reduced risk of a blowout. I've towed 5,500 lbs 35,000 miles with the Touareg.

Jimbuffalo2 · Sep 13, 2018

Thanks for the input. I'll put together some data points for all to ponder.

Aside from the inconvenience/cost of feeding this new lust for AdBlue, the Touareg is performing in Beast Mode. I discovered some sections of highway I definitely want to drive again.

@buckwheat: The percentage info is not that far off...and I am seriously using the power band. In my head, I might be close to the 4%.
@gazaflash: Airfoil. Yes. Almost obvious in retrospect. Where were you when I was loading this thing? (If I could, I'd post a pic,)

@Xcentric: Good advice to slow it down.

Shout out to Josh at Findlay VW in St. George Utah. He topped it with 2.5USG of the VW approved juice and I was quickly on my way. For those keeping score at home that's 7.5 gallons in 4400 miles....again with towing at near capacity for half that distance

I'll be able to compare pre and post towing consumption and will update.

In the meantime, pack some AdBlue if you're hauling a load. Again, I have nothing to compare to towing pre-Fix...but the "fix" is clearly doing its job dosing AdBlue n these quantities to compensate for 14mpg diesel consumption

Cheers

Ionman · Sep 13, 2018

I've done this with my 2004 V6. I did full calculation with similar dimensions as well, hauling similar.

Trailer was a 4ft x 8ft utility, modified with a 16in set of tires and new axle to match.
(2) 14' Hobie Outback kayaks
(4) MT bikes
(1) dual solar panel for boondocking.

So, to answer the questions:

a) Mount the kayaks on the Touareg with the roof box on the Tiguan?

No. If you can, mount it to the sides, with the top of the kayaks flushed to the body. Wish I saved the pictures before my phone ended up in the deep lake to snow.

b) Mount the roof box on the Touareg and the kayaks on the Tiguan?

Mount the box on top of the trailer when possible. Don't do it for the Tiguan. Drag is greater at the front than it's at the back, assuming your trailer is lower than your Tiguan. If your kayaks can't be mounted on the side of the trailer, then mount them on top of the trailer, with the box on top of the Tiguan. The drag on the box will minimize any drag from the kayaks.

c) Mount them all on the Tiguan?

Your roof won't be able to handle them all, or rather, the overall weight will exceed the roof's capacity. Drag will also be horrendous.

d) Mount them all on the Touareg?

Same as C.

We hauled our trailer fully loaded over 10k, up to Washington and over to Texas from California. Fuel data was closely observed as well, with and without the fully loaded trailer, with and without the setup.

As many have said before me, the gap between trailer and vehicle must be as little as possible. I measured mine out to be 38in for the gap between the hatch, with a 38° deflector hatch to streamline the top of the trailer. Best configuration I have so far.

Towing Aerodynamics - just for grins

Jimbuffalo2

Patr80l

Jimbuffalo2

FSJ Guy

buckwheat

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Jimbuffalo2

nickyt

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Jimbuffalo2

buckwheat

tadpole

gazaflash

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Xcentric

Jimbuffalo2

Ionman

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