LM- Aerodynamic drag effect on tow rating

I tow an enclosed trailer ALOT for work with most recently a '14 Suburban that has a tow package. It has been a great truck, just turned 235k miles but it has had enough and it is time for a new truck, bad timing. The tow capacity is ~8000#, our trailer is 5000# and has brakes and a weight distribution hitch. I always felt I was was in the "ideal" weight range for a 1/2 ton truck, as in I wasn't maxing out the tow vehicle's systems. Until recently I hadn't thought about drag possibly adding "weight" into the tow capacity equation. I know that my open trailer with a 3500# car on it (~5k# total) is just barely noticeable behind the truck but the enclosed 7' x 16' at about the same weight puts some serious strain on it. So is there a general rule of thumb that "X" square footage of frontal area adds 1000# to the towed "load weight" at 60 MPH? Or is it just a case of the engine and transmission having to work harder due to the poor aerodynamics with no "weight" difference? I understand the faster you go the more the drag increases, most of the trailering I do is at highway speeds. 

TLDR; Does aerodynamic drag effect tow rating "weight" ? i.e. a 5k# enclosed flat nose trailer really "weighs" 8000# to the engine and transmission at 60 MPH. 

Am I overthinking this?

This a screenshot from the Ford Towing Guide - you might be able to extrapolate 

In reply to Rons :

That is a cool chart and I went to Ford's site to see what else they mention, but nothing is said about how this effects the overall weight rating. Although based on the above it does appear that drag needs to be figured into the equation. 60 square feet seems pretty small, the grille on an F250 has to be almost that big!

IIRC, the tow testing is done with something that simulates the "worst case scenario" which would be a bumper-pull box trailer.  The GMs I saw testing used a Wells Cargo (or similar) trailer that was loaded with those big caged poly tanks full of water.

Having said that, my biggest concern is not aero drag, it's billboard sails.  When you do a travel trailer or enclosed trailer, you're dragging a billboard.  The concern I think is that it will push you sideways into a ditch before the drag causes issues.

But yes, aero drag will make the truck think you're pulling more weight than if it were a flatbed with a corvette on it.  I never concerned myself with "overloading" because of drag because there is often a generous dumb-ass factor built in with ratings.  It just stands to reason to my logical brain having worked in that industry (on the design side more than engineering) that if a manufacturer is going to make a blanket statement about tow ratings, they have already assumed that the number is equally suitable for a 16 year old towing a travel trailer and for a seasoned pro towing a flatbed with a few pallets of something on it.

In reply to Curtis73 (Forum Supporter) :

My thinking has been the aero effect can be overcome with more engine/trans... the billboard effect requires a better chassis, or better sway control. 
I've never narrowed it down to numbers, but have experienced lacking in all of the above!

Most "newish to towing" folks tend to focus on either one or the other. And I've seen factory ratings be off of safe numbers by thousands - in either direction  So my trust in their testing methods don't go far 

In reply to 03Panther :

We definitely agree on that.  Case in point:

1996 Caprice with tow package = 5000 lb towing
1996 Impala SS, which includes all the tow package options, plus adds 3.08 gears, stiffer springs, an additional PS cooler, and better shocks = 2000 lb towing.

Their testing methods aren't the problem.  The engineers spend years crunching numbers, following ASTM-prescribed testing, do real-world testing in Alaska and Arizona, then the accountants and marketing team step in and assign their own numbers.  In the case of the Caprice/Impala above, the marketing team knew that most people weren't buying the SS to be a tow pig, and the accountants knew that lowering the tow rating could save them millions in warranty claims and liability, hence why the SS got a lower tow rating despite being arguably better-equipped to tow.

Regarding the chassis/sway vs drag/engine, I do know that OEMs test with kind of worst-case scenarios for the most part.  They would have serious egg on their face if they tested an F150 with a flatbed at 9000 lbs, then customers put a 7500-lb travel trailer behind it and it constantly overheated, or the transmissions burned up.

It's all a big numbers dance.  Ever wonder why every single truck on the planet has a GVWR that corresponds exactly to the DOT weight class ratings?  If you take a truck from each manufacturer, all of them rated for 8500 lbs, and put payload in them to make them that exact weight, they will all handle the load completely differently.  Couple that with the fact that you can (in most states) legally register your truck for the weight you want instead of what it can actually handle and you can see it's more of a money/numbers game.  But to say that a Toyota Tundra will handle the same weight in exactly the same way as a Silverado, F150, or Nissan Titan is somewhat obtuse.

You also have to consider a lot of other things.  My 02 F150-7700 (heavy half) kinda sucked towing my 3500-lb boat.  That was because the previous owner replaced the factory D-range tires with.... not C-range, not even standard LT.... but P-metric passenger tires.  When I bought the 94 Branger, it was actually better at towing the same boat because it had proper tires.  Although, I will say the 5.4L in the F150 was certainly better than the 4.0L in the Branger at overcoming drag.

Thanks for all the input. As I originally thought, I was over thinking this. Sure, the engine and trans may work a little harder towing the enclosed trailer but well within their capabilities.  However, I have had enough of towing with 1/2 tons and will be moving to an F250SD. That should mean much less stressful trips when towing in the future. The work trailer was initially very skittish but I discovered i had it loaded poorly and once the load was distributed better it tracks very nicely. It even handles heavy wind gusts and truck wash well when loaded. Thanks again 

I just did some quick math (subject to error, so do your due diligence), and here's a simple metric. At 70mph, the drag is 2.4hp per square foot, assuming a drag coefficient of 1. Simply multiply that 2.4hp by whatever coefficient you deem appropriate. So if you have a boxy trailer that is 8.5'x5'=42.5ft^2, then it will cost about 100hp just to pull at a steady 70mph. This obviously doesn't account for the weight of the trailer and load or friction, so it is just to give a ballpark. Also remember that even with a torque engine, you won't be at peak power at cruise. If you are cruising at 2,500rpm and only have 150whp available at WOT, you're transmission will be busy.