Tow Capacity and the 80% rule

[KYAvion]

Many say not to exceed 80% of a vehicle's max tow capacity. I'm curious how many follow this, and if not, why not?

I imagine on flat terrain, towing at 100% of a vehicle's max tow rating wouldn't be that big of a deal. In hilly or mountainous areas, however, I imagine the 80% rule comes into play. Question is where to draw the line? Thoughts? How much is too much? What if one doesn't pull their trailer very often? How often can one tow at the max and it not be an issue?

[Rostam]

IMO, very few vehicles shine at their max towing capacity (even if its a diesel dually). So the the 80% rule makes sense to me. Incidentally, we are towing exactly 80% of our vehicle's max towing capacity (towing 6000# with a vehicle rated at 7500#).

IMO, how much a vehicle can tow depends on a lot of factors. Terrain matters a lot. Towing in flat lands that does not get too hot is very different than towing grades in heat of the summer. How much you tow matters as well. If you tow infrequently and mostly locally, IMO, you can push the towing limit. Not so much if you travel coast to coast every year. Experience matters as well. IMO, drivers that have vast towing experience are more comfortable pushing the towing limits. Tow vehicle wheelbase and weight (relative to the weight of the trailer) also matters. Finally, a properly installed/setup weight distribution hitch with sway control can make a big difference -- It does not increase towing capacity, but will make towing safer and less stressful.

At the end of the day the 80% rule is just a rule of thumb. And different thumbs look different It could be that someone is not happy towing at 70% of max towing capacity and someone else is happy at 100% towing capacity. The only way to find out is to tow and after a while you'd know if you are OK or you need a more capable vehicle. IMO, most people upgarde their tow vehicles because towing with an under-powered, under-braked, and under-chassised vehicle is very tiring.

I would try a setup before jumping to any conclusions, as long as important towing numbers are not exceeded. What you can pull depends on towing capacity and GCWR (GCWR is usually more restrictive). What you can haul in your tow vehicle depends on axle ratings and GVWR (GVWR is more restrictive). You also need a receiver that can handle the tongue weight of the trailer.

[silverloaf]

Many say not to exceed 80% of a vehicle's max tow capacity. I'm curious how many follow this, and if not, why not?

I imagine on flat terrain, towing at 100% of a vehicle's max tow rating wouldn't be that big of a deal. In hilly or mountainous areas, however, I imagine the 80% rule comes into play. Question is where to draw the line? Thoughts? How much is too much? What if one doesn't pull their trailer very often? How often can one tow at the max and it not be an issue?

Until fairly recently, calculating towing capability was a crapshoot among automakers. There was no standard to compare one vehicle against the other. That changed with the introduction of SAE J2807: "Performance Requirements for Determining Tow-Vehicle Gross Combination Weight Rating and Trailer Weight Rating." Toyota implemented it in 2013, followed by the Big 3 in 2015. Here's a website on the subject:
https://www.edmunds.com/car-reviews/fea ... tings.html

While at Ford, I spent a few weeks doing hot weather development testing in Arizona. The "Davis Dam" test mentioned in the article is brutal. Pulling a load, AC on, foot to the floor, 11 miles up a mountain pass at 100 degrees ambient temperature. It's done 3 times to qualify the vehicle under a specific load.

The test is only a reference point. Even with this procedure, it is difficult to determine how it relates to real-world towing, especially over time in service. This is why the non-scientfic 80% rule has some degree of credibility, especially vehicles built prior to the standard being implemented. The cooling, in particular, becomes very finicky over time.

I ordered a new truck last Saturday to pull our Avion. It has a 48% (or 5100 lb.) towing capacity reserve between the trailer and tow vehicle. I didn't spec it out as much for max towing as for features to keep the powertrain running more efficient with less transmission shift busyness/lugging in mountainous terrain.

[Overdrive]

I don’t think I ever towed the max capacity of my diesels. I’ve towed some pretty big trailers and some not big but very heavy. I have two 7.3 diesels same configuration on the body and drivetrain except one is a single wheel auto Trans and the other is a dual wheel manual Trans with a gearvendors overdrive.
The dually is a way better tow vehicle overall. The single wheel is a F250 and it tows great. It’s rsted for less power than the F350 even though they are both 7.3. And it’s noticeable. Not bad but I can notice it
The dually simply out tows it uphill and overall because it’s running 4:10 vs 3:73 gear ratios and a manual combined with the gearvendors gives me that much more throttle and gear control.. And with no gearvendors engaged the F350 gets about 4-5 mpg less than the F250 which gets around 18/19. Once I use the gearvendors that narrows to about 16 mpg from a 11/12 mpg from the dually.

I wouldn’t want to tow the max with my trucks.

[66Avion18]

While rather late to the thread, we only just purchased a '66 Avion Sportsman. Before purchasing it I checked with our dealership on towing capacity of our Jeep Cherokee equipped with a factory towing package. They suggested not to exceed 2/3 the stated towing capacity. In our case that is 4500 lb, so 3000 lbs.

This number (proportion) meshes with a 'towing' course I took many years ago while working for a major US based seed company. We regularly towed research equipment with both 1/2 and 3/4 ton trucks. The course instructor suggested never to exceed 70% of stated towing capacity.

Kevin

[silverloaf]

Yours is certainly prudent advise.There is a tendency to think the towing specifications on the door jamb have no limitations on time in service. Many people are perplexed when their new tow-friendly vehicle takes a dump 6 years later in the mountains of Colorado.

There is a lot to be said about having a dedicated tow vehicle. It is easier to manage its maintenance history than using it as a daily driver. I don’t have that luxury but am fully aware of its expectations and limitations when assigning it to tow mode.

[Roy Turbett]

What many people don't realize is that the manufacturer's stated tow capacity assumes that the only thing in the tow vehicle is a 150 lb. driver. I tow my 28 ft. Avion that has a GVWR of 7900 lb. with a seven passenger 2016 Lincoln L that has a stated tow capacity of 8300 lb. and a maximum payload of 1479 lb. According to the 80% rule, I should only be towing a 6640 lb. trailer. And this is a good rule of thumb because it accounts for the additional payload you're likely to carry in the tow vehicle that also includes the tongue weight of the trailer. For example, if I deduct the weigh of another six 150 lb. passengers (900 lb.) and the tongue weight of a 6640 lb. trailer (approx. 664 lb. to 996 lb.) I end up slightly over the 1479 lb. payload capacity. But I usually travel with only one other passenger.

I took my truck and trailer to be be weighed in order to see if I'm within the stated towing and payload capacities. The first trip I just weighed the truck that just had me and some tools and other miscellaneous items I always carry. The second trip I took the truck and trailer that was loaded with all my standard trailer supplies but no water or propane. Here are the specs and actual weights.

2016 Lincoln Navigator L Factory Specs per stickers
GVWR 7900
Front GAWR 3700
Rear GAWR 4330
Payload 1479
Curb weight 6421 (7900 - 1479)
GCWR 14900 (per owners manual)
Max tongue 600 base or 900 lb. w/ wt. distribution hitch

Per towing guide
Max tow wt. 8300 (Assumes 150 lb. driver and no cargo)
Tongue wt. = 10% to 15% trailer wt.
Max. Trailer wt. = 6000 lb. to 8300 lb. considering all factors

14900 GCWR (per owners manual)
-150 lb. driver
-6421 curb weight (my 2016 Lincoln Navigator L)
= 8329 tow capacity

My unconnected weights
Truck 6780 (Just me and a few tools I always carry)
Steer axle 3400
Drive axle 3380

My connected weights
GCW 13420
Steer axle 3420
Drive axle 4020
Trailer axles 5980
Trailer wt. 6640 (1979 Avion 28’ inc. essential gear)
Tongue wt. 640 = 9.6% of trailer weight

Remaining payload in truck
7900 (GVWR of truck)
-6780 (Includes driver and a few tools)
-640 - 790 (hitch weight assuming 10% of trailer)
= 150 - 480 lb. remaining passengers and cargo

Remaining trailer capacity
7900 (GVWR of trailer)
-6640
1260 lb. gross remaining trailer payload

Likely remaining trailer payload
1260
-542 (65 gallons water)
-80 (propane)
=683 lb. remaining trailer capacity

The bottom line for my trailer is that the Navigator won't have any trouble towing it as long as I watch my weights. I'll be taking a trip west with just one passenger so I'll remove the two rear captain's chairs to save some weight for the passenger. I'll still have the third row seat if needed.