Tongue Weight and trailer GVWR

[wulfraat]

I go by axle ratings. My axles at 4,400 lbs each. I make sure that I don’t place more than 4,400 lbs load on them when hitched up period. My GVWR is 8,800, which is determined by Max axle rating.

For instance, the only material structural difference between my 2017 8,800lb GVWR 30’ international and the 2017 30’ classic with 10,000 GVWR are the axles. The 30’ classic has 5k axles and the international has 4.4K axles. I’ve reviewed structural diagrams provided to me by airstream / discussed with airstream and consulted after market uplifted timeless travel trailers when I was loading 275lbs of Lithium batteries and equipment under the rear bed.

Don’t over think it. Just make sure your axle loads are at or below GAWR when hitched up. For what it is worth when hitched I only load about 7400 lbs on the axles wet and ready for camping (~8,500lbs total trailer frame load when you include tongue weight on the truck, but I know my frame/shell is good for 10k lbs [emoji6] ). GAWR is what matters most due to the rubber used in dexter torsion axle along with brake drum size.....along with relatively even load distribution inside the trailer

That’s my opinion and I’m sticking to it [emoji4]

[NickA]

Thanks for all the replies! Along with them, I've read so many articles and I'm still unclear. We started RVing recently and did head to the cat scales on our first trip. The numbers were all higher than we expected, so I started to weigh everything to make sure I understood.

The factory unloaded weight we expected from the Airstream website was 5868lbs (with propane and batteries) and the GVWR is 7600. However the sticker on the trailer shows 6245lbs which I think excludes the ~110lbs of propane+tanks. That means we’ve lost 28% of the expected cargo capability before we even start. We did select the second AC unit and the rear hatch, but I didn’t expect that to sum to nearly 500lbs!
We’ve since added a 200lb Hensley hitch and solar with 3 lithium batteries, summing to a further ~200lbs. Fill up the fresh with 37gal (another 308lbs) and add another 150lbs I can’t account for and everything else that I can, and it matches what we measured at the CAT scales. That leaves us just 400lbs left for everything excluding trailer/hitch/solar/water.

While the 200lb hitch is mounted on the trailer, half of its weight and half the solar batteries under the bed (at the front in a 27FB) is borne by the truck, especially with a weight distribution hitch like ours, and is not on the axles. The axles combined are rated to the same 7600 number. As such, I really struggle to understand why that doesn’t effectively come off the trailer rating, and that extra margin (~200lbs) would really be nice! Unless it’s a limitation on the Jack, which seems unlikely and isn’t specified, how can weight borne by the truck via the tongue still be counted in the trailer number?

As a silly example of - if I placed a 100lb weight on the hitch receiver (ie on the trailer) or the same weight on the tow bar 2 inches nearer the truck (ie on the truck), this argument would say one subtracts from the trailer’s GVWR and one doesn’t. However, in all meaningful ways they are identical while driving, and would be on the jack while not. Doesn’t make much sense to me. What am I missing?

[knight-rider]

GVWR and tongue weight topics are so much fun to discuss. GVWR is the actual weight of the trailer. Tongue weight is the downward weight exerted by the tow ball on the tow vehicle at the pivot point. Same things with axle load - it’s the weight exerted at each axle. Silly analogy - think of your grandpa with a walking stick. The combined weight might be say 80 lbs, but he might be putting 10 to max 20 lbs pressure on the ground through the tip of the stick - depending on how strong grandpa is - but that doesn’t mean grandpa’s weight keeps changing. His weight on each foot might vary, and that’s similar to axle load. Combined weight is always constant, but the downward pressure might change; however, it cannot exceed a certain limit. Grandpa would never put more than 80-100 lbs of weight on his foot, even with a backflip, unless he puts on extra weight. Bottom line - don’t mix up GVWR with tongue weight. If you transfer more weight to the front of your trailer, then tongue weight would increase but GVWR would remain the same! If you transfer weight to the rear of the trailer, tongue weight might reduce, but it’ll make your rig highly unsafe. I don’t want to get into the details of how all of this is calculated. As folks mentioned, stay under OEM specs for axle load, GVWR, and tongue weight. TW is a bit debatable. Some say if axle load is under OEM limit, TW is not a problem. I don’t necessarily agree. The way you load the trailer and the critical points where pressures are exerted changes axle load and tongue weight. If you use a long pulley, you can lift 50 lbs by putting say 5 lbs pressure, but without a pulley, you need to put 50 lbs pressure. Same logic - axle load and TW is based on downward pressure and weight distribution. If you put 100 lbs on tongue versus 100 lbs in TV cargo, it would put different amounts of pressure on the axles. The former option would put more pressure on the rear axle through hitch pivot point. The latter would be easy on axles because the weight gets evenly distributed by the TV. If you transfer 100 lbs right near the tow bar, it would put more pressure on rear axle.

[dog_and_cat]

Originally Posted by NickA

"The factory unloaded weight we expected from the Airstream website was 5868lbs (with propane and batteries) and the GVWR is 7600. However the sticker on the trailer shows 6245lbs which I think excludes the ~110lbs of propane+tanks. That means we’ve lost 28% of the expected cargo capability before we even start. We did select the second AC unit and the rear hatch, but I didn’t expect that to sum to nearly 500lbs!"

Not that it's to be trusted but the Airstream website shows the base weights as including "LP and batteries".

[NickA]

Originally Posted by knight-rider

If you put 100 lbs on tongue versus 100 lbs in TV cargo, it would put different amounts of pressure on the axles. The former option would put more pressure on the rear axle through hitch pivot point. The latter would be easy on axles because the weight gets evenly distributed by the TV. If you transfer 100 lbs right near the tow bar, it would put more pressure on rear axle.

Our hitch is a Hensley hitch (not the standard ball), and pretty rigidly holds the two together. Isn't that half the point of the weight distribution aspect of the hitch? As such putting weight just one side vs just the other should be the same from a weight distribution perspective.

Originally Posted by knight-rider

think of your grandpa with a walking stick. The combined weight might be say 80 lbs, but he might be putting 10 to max 20 lbs pressure on the ground through the tip of the stick - depending on how strong grandpa is - but that doesn’t mean grandpa’s weight keeps changing. His weight on each foot might vary, and that’s similar to axle load. Combined weight is always constant, but the downward pressure might change; however, it cannot exceed a certain limit. Grandpa would never put more than 80-100 lbs of weight on his foot

This is kind of my point. He’s unable to lift his whole weight on his legs (equivalent to GAWR), so he exerts some of it on the stick (like the tongue). As such, his GVWR would have to be the sum of his legs and the stick or he'd be exceeding it when leaning on a fence (the jack). To me this seems the same as the trailer exerting some of its weight on the TV while staying under the axle limits. Here’s an example…

- Trailer weight 7000 standalone before hitching (including axles and jack)
- TV weight 5000 ignoring tongue weight
- Trailer weight exerted on TV tongue 1000

Here, TV axles supports 5000+1000=6000lbs and trailer axles 7000-1000=6000lbs. TV GVWR has to and does include the extra 1000. That 1000 isn’t supported by the trailer axles, so why does it have to be included in the trailer GVWR? Otherwise it’s counted twice – in both TV and trailer GVWR. Our trailer GVWR is the sum of our two GAWR numbers, so it’s not like they already took this into account. The extra weight still isn’t on the axles when decoupled, as it moves to the jack.

[superChop]

I probably should not ask this question, but here goes. I enjoy all discussions about TV's and their ability to tow different types of trailers and this is a discussion on the trailer weights. So I took your recommendation and read your excellent explanation on your blog, "Married with Airstream". It was very informative and should be available on this Air Forum as a must read for people new to towing, since your explanation is not limited to Airstreams.

Quick question that may be based on mis-reading your article. Payload was defined on the blog as subtracting Curb Weight from GVWR. In your example of your F150, listed GVWR is 7700 lbs and Curb Weight 5586 lbs. Using your explanation this should provide a payload of 2214 lbs, however the payload listed for your F150 is 1533 lbs? Confirming your formula, my F250's GVWR is 10,000 lbs with a Curb weight of 6495 lbs. Payload on the truck confirms payload at 3,505.

This might be too much trivia, but I got the time and curiosity so it is time to hit the "submit" button.

[knight-rider]

Originally Posted by NickA

Our hitch is a Hensley hitch (not the standard ball), and pretty rigidly holds the two together. Isn't that half the point of the weight distribution aspect of the hitch? As such putting weight just one side vs just the other should be the same from a weight distribution perspective.

Hensley locking system helps with the sideway movement by projecting the pivot point to rear axle. The connection is still at the tow ball, and the weight distribution system is just like any other system. It transfers some weight to the front axle, depending on how much you tune. When I called Hensley, they told me to not even consider the hitch weight while calculating the tongue weight, but either ways if you stick to their manual and keep it at mid setting in the vertical jack, the weight transfer might be 20-30%. But that doesn't mean the trailer axle is free of tongue weight. For ex: If you have a 20' long tongue (hypothetical), then your trailer axle would bear the majority of the tongue weight. So it's not a simple math of adding tongue weight to TV's GVWR.

Originally Posted by NickA

This is kind of my point. He’s unable to lift his whole weight on his legs (equivalent to GAWR), so he exerts some of it on the stick (like the tongue). As such, his GVWR would have to be the sum of his legs and the stick or he'd be exceeding it when leaning on a fence (the jack). To me this seems the same as the trailer exerting some of its weight on the TV while staying under the axle limits. Here’s an example…

- Trailer weight 7000 standalone before hitching (including axles and jack)
- TV weight 5000 ignoring tongue weight
- Trailer weight exerted on TV tongue 1000

Here, TV axles supports 5000+1000=6000lbs and trailer axles 7000-1000=6000lbs. TV GVWR has to and does include the extra 1000. That 1000 isn’t supported by the trailer axles, so why does it have to be included in the trailer GVWR? Otherwise it’s counted twice – in both TV and trailer GVWR. Our trailer GVWR is the sum of our two GAWR numbers, so it’s not like they already took this into account. The extra weight still isn’t on the axles when decoupled, as it moves to the jack.

Some part of 1000 lbs is actually carried by the trailer's axle. This is why you notice that dual axle 23' trailers have less tongue weight compared to 20' or lower single axle trailers. For ex: FC 23' FB has 6000lbs GVWR and 430 lbs tongue weight, but 20' BC 20 has 4300 lbs GVWR and 530 lbs tongue weight, and Bambi 16' has 430 lbs tongue weight. If the entire tongue weight is on TV, then dual vs single axle should not make any difference to the tongue weight. But that's not true. When we are cutting close to axle load, some people play around with tire pressure to handle the risks of understeer/oversteer, and some people don't mind cutting close. Please also note that you would never evenly distribute the load on TV's front and rear axle when you are hitched. The rear would ALWAYS take more load compared to front. If you tune WD to max to distribute 50-50, you would have a very rough ride. But whatever it is, the reading you get from CAT scale for axle loads is the most accurate assessment of your rig.

[SYC2Vette]

I know this has been covered to death, but especially for those new to trailer towing and camping in general the GVWR (or more directly and importantly payload) and max GAWR is super important to understand and very often where we hit the limit (rather than hitting max trailering limit).

When we were looking at tow vehicles and potential AS before we dialed in on our 20' FC and our mid size Canyon, I was astonished that several of the F150 Ford trucks I looked at had lower payload ratings than the midsize Canyon/Colorado. If we ever go to a larger Airstream we will likely go to an F150, but thanks in large part to this forum, I have learned to really pay attention to the payload which in the case of the Ford F150 apparently ranges from 1150 lbs (yikes that is pitiful) to over 3,000 lbs! (HD towing HD payload).