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Old 12-10-2012, 08:23 AM   #1
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What do you do with the extra "water" impact on payload?

My status as newbie remains in place as I have only towed the unit home from the dealership through the low mountains out of Los Angeles along I-1- to Phoenix and parked in an under roof storage location. I will be back home from the "refreshing" cool air of the Midwest to the warm air of the desert SW next week. My first trailer activity will be to rotate the five OEM GYM "ST" tires through the Costco tire facility and magically transform them to Michelin LTX (P) 235/75R15 XL tires that I paid for several weeks ago.

I know my existing tongue weight from a hydraulic scale I bought before picking the trailer up at the dealer and it weighs with virtually no "stuff" 1,150 pounds. I plan to dump the few gallons of water the dealer put in the fresh water tank and remove any of my non fastened "stuff" (except for the sheets cause they were an interesting experience to put on) like tools, Dish TV antenna etc go to the CAT scales and get a true nearly empty weight without the TV attached. Then I will attach the TV with my current Hensley settings and see the numbers on the axles.

Next I will fill the fresh water tank to determine the net useful load by crossing the scales in a similar manner as before.

I have not seen any posts concerning the decrement to useful payload load generated by full black and gray water tanks. If there is no dumping facility when leaving a location and one goes onto a public road, the GVW now includes, in my case, 39 gallons of black water [guessing 390 pounds here] and 37 gallons of gray water [guessing 320 pounds here] or about 710 pounds of temporary load in addition to the balance of fresh water still in that tank (39 gallon capacity at about 330 pounds) that is located between the axles. Those two tanks are forward of the axles so there will be some more weight added to the tongue weight as well. There would still be six gallons in the water heater and perhaps two gallons floating around in the pipes.

The factory specification for my trailer without options is a 1,748 pound payload.

Obviously, the real world would not generate all three tanks at maximum capacity at the same time. What percentage of the, in my case, theoretically 1,110 pounds of water in various flavors, do you use when calculating the useful load for your trailer? BTW, I do know there are some models of AS with a single combination gray/black water tank, but the thought process is still the same.

This thought process impacts tire selection when considering the various safety margins discussed in this area.

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Old 12-10-2012, 08:42 AM   #2
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Fresh Water 39 gal, Black Water 39 gal, Gray Water 37 gal.

I guess that allows you to fill up the fresh tank again before needing to dump, assuming that the used water divides pretty evenly between gray and black. But you're never going to have all three tanks full at the same time. Worst case is a full fresh tank and the black and gray tanks half full. From that point on, the fresh tank is going down and the black and gray are going up. I don't see any practical camping scenario where you will have more than 78 gallons of water on board.

It will be an exception if you get to 78 gallons. When you fill up the fresh tank, you will most certainly be able to dump the gray tank, even if you can't dump the black, so you might wind up with 39 gallons of fresh, 20 gallons of black, and zero in the gray.


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Old 12-10-2012, 09:31 AM   #3
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You can figure water (fresh, gray, or black) at about eight pounds a gallon. You'll be very close.

A lot (if not all) of the figuring on tank weight issues will depend upon how you use your trailer vis-a-vis water usage.

I personally have never had all tanks full or even nearly so. Note that on most units, the fresh water tank full can be emptied into either or the gray or black tanks entirely (not usual every to do this, but in case you left a faucet running .... etc.). Usually, there is a differential about where the water goes, so in most cases, if and when you run out of fresh water, it's just distributed between the gray and black tanks. The distribution varies on how and what you wash / bathe, and toilet facility use. I think that the received wisdom is that given an unlimited amount of fresh water, the gray tank will usually get more flow and will tend to fill before the black tank ... that has certainly been my experience.

In my case, unless it's cold weather, I always start a trip with empty black and gray tanks, but full of fresh water. From there, things change, depending upon whether I'm boondocking or not. If I'm boondocking (which is usual), I might have along a 7 gallon extra water container. In this regime, I've never filled either gray or black tank, and the total trailer weight never changes, except for the weight of the additional 7 gallons of water ... and when I get to the nearest place to dump tanks, the weight actually goes down below where I started. If NOT boondocking, you might have a fresh water spigot available, so that you COULD in theory fill all tanks to the brim. I've never done so, but it's possible. But then most places that have fresh water available on-site also have a dump station so that you can dump the gray and black tanks occasionally and at least before departing. That way, you're going down the highway homeward bound with (worst case scenario) a full fresh water tank, just as you started out. So fundamentally, when I think about trailer carrying capacity, I just base it one ONE full tank.

I expect that you'll see when you weigh with fresh water tank full, you'll be able to pack a lot of clothes, food, cooking gear, etc. into the trailer.

Based on scale weighings, in this sort of usage, with one full tank and with my weight distribution set where I like it, with the trailer full of the "stuff" I use when camping (for up to a month or two at a time), I'm always several hundred pounds (500-600) below max. trailer weight. And since I tow with a 3/4 ton diesel, I can pack a LOT into the truck ... and have never even come close to GVW for the truck.

So load up, go weigh, set the hitch right, and then get out there and have fun!
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Old 12-10-2012, 09:32 AM   #4
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I agree with Zep, well sort of, and I never figure more than the water in the fresh tank plus the water heater, which in our case is 56 gallons. As you use that water, it just gets sort of moved to the other tanks, and at 8.35 lbs/gal that's 468lbs.

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Old 12-10-2012, 10:22 AM   #5
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When making a tire selection I would consider all of that and add 10%. You don't want the load to exceed the combined tire weight rating.

1966 Mercury Park Lane 4 DR Breezeway 410 4V, C-6, 2.80 - Streamless.
1966 Lincoln 4 door Convertible 462 4V 1971 Ford LTD Convertible 429 4V Phoenix ~ Yeah it's hot however it's a dry heat!
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Old 12-10-2012, 10:37 AM   #6
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That i why you will see many threads of switching to a 16" rim from the factory 15". The factory does it because it is less expensive and just meets the load. In fact I would not doubt they dial down the trailer weight ratings to be with in the tire load capacity. That is just an un-proven opinion.

The 16" rim will give the user much more load capacity options.
Don't over load as this situation is a tire killer.


1966 Mercury Park Lane 4 DR Breezeway 410 4V, C-6, 2.80 - Streamless.
1966 Lincoln 4 door Convertible 462 4V 1971 Ford LTD Convertible 429 4V Phoenix ~ Yeah it's hot however it's a dry heat!
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