Payload Tolerances: how close to max is too much?

[ReluctantTraveler]

I've been running a bunch of numbers on both a Total Composites build and a DIY habitat (using wood framing and XPS insulation similar to what @IdaSHO did).

I've had numerous folks mention that an F-350 can't handle the payload, but according to Ford a 12,400 GVRW vehicle has a max payload of 4,580 lbs. My math indicates that would leave me 700lbs of payload capacity after accounting for people, water, provisions, and toys.

I haven't driven a truck since my dad had an F-150 when I was in high school, and have no basis for how running that close to max payload would affect handling. I'm also not even sure you can actually buy an F-350 SRW with 4,500lbs of payload, but having an SRW vehicle without needing to do a conversion is appealing.

I've attached the calculations I put together, if anyone wants to rip apart my math and point out places I've cleared got it wrong.

I've added a 10% "margin of error" number in there, and assume both the 60 gal fresh and 40 gal gray tanks would be completely full. Four people plus a 15lb dog would be traveling in it.

 

[ReluctantTraveler]

Doh, forgot to account for the electric jacks, which reduce that remaining payload to 400lbs or so (if we bring them with us, which we likely will).

 

[IdaSHO]

With regards to GVWR, I wouldn't use ours as an example...
while we do it as safely as I can muster, we run considerably over max GVWR.

 

[simple]

did you add shipping into your costs?

Also doesn't look like you accounted for cabinetry and fasteners.

 

[ReluctantTraveler]

did you add shipping into your costs?

Also doesn't look like you accounted for cabinetry and fasteners.

I did not add shipping. A lot of the materials are available locally, with the exception of the windows/door. But that's also definitely a miss on my end. Good catch. That will obviously drive up the price!

I did account for cabinetry in the habitat section. I plan on building them out of the same marine ply, and was too lazy to break that out into a separate section.

 

[ReluctantTraveler]

With regards to GVWR, I wouldn't use ours as an example...
while we do it as safely as I can muster, we run considerably over max GVWR.

I was aware of that, actually. I've seen your threads on the math you did and why you feel comfortable doing it.

I referenced your camper as a basis for the construction technique/general build approach I would use if I went fully DIY.

My question on "how close to max payload is ok" still stands, though. I wouldn't personally want to go over.

 

[ReluctantTraveler]

I guess I should also add: I'm not looking to build some bada$s off-grid apocalypse vehicle.

What I DO need is something that we can comfortably spend 1-3 months on the road in while exploring more of the US.

Our travel trailer + SUV rig is workable, but towing sucks, and the lack of off-grid solar and a tiny water capacity limits both where we can camp and our ability to make impromptu stops between camp (because we travel with a dog and parking with a trailer is hard).

I want a manageable driveable, and if it can fit in a normal parking space, all-the-better! (another appeal of an F-350 over the F-550).

 

[tacollie]

Keeping the cog in front of the axle and keeping the weight low as possible will be key to good handling. I would consider adding a Hellwig rear sway bar. I wouldn't be worried about handling.

For maintenance reasons it's recommended to stay under 75% of payload. Running at gvwr will most likely increase wear and tear so you will need to stay on top of maintenance.

 

[calameda]

I don’t know the details of your planned construction, but your habitat weight seems very low, especially with all that marine ply. I have a TC flatbed camper, opted for some reinforcement in the rear wall, and I came in well over your shell weight.
40 gallons is a huge amount of gray water.
Flatbed weight seems quite low, but have no idea what you envision. No under-bed boxes? No headache rack?
Need to attach the camper to bed, what will you use? Torklift Fastguns + brackets bolted to flatbed will probably be 50 lbs
Quite a few other weights are pretty obviously low: 3 empty water tanks can’t possibly be 6 pounds, Lagun mount can’t be 1 pound, the Tern door definitely more than 15 lbs, 4 Tern hatches can’t be 2 lbs, you’ll need a MaxxFan for ventilation or something similar
You haven’t accounted for plumbing and wire and power distribution.
Account for fuel and tanks for heat system.
only 5 lbs for tools? and no recovery gear?

this is a start

 

[ReluctantTraveler]

Keeping the cog in front of the axle and keeping the weight low as possible will be key to good handling. I would consider adding a Hellwig rear sway bar. I wouldn't be worried about handling.

For maintenance reasons it's recommended to stay under 75% of payload. Running at gvwr will most likely increase wear and tear so you will need to stay on top of maintenance.

That's a good target number! Thanks for putting a stake in the ground!

Sway bar is a must, IMO, and my plan is to put the batteries and water up front for CoG reasons, as you noted.

 

[ReluctantTraveler]

I don’t know the details of your planned construction, but your habitat weight seems very low, especially with all that marine ply. I have a TC flatbed camper, opted for some reinforcement in the rear wall, and I came in well over your shell weight.
40 gallons is a huge amount of gray water.
Flatbed weight seems quite low, but have no idea what you envision. No under-bed boxes? No headache rack?
Need to attach the camper to bed, what will you use? Torklift Fastguns + brackets bolted to flatbed will probably be 50 lbs
Quite a few other weights are pretty obviously low: 3 empty water tanks can’t possibly be 6 pounds, Lagun mount can’t be 1 pound, the Tern door definitely more than 15 lbs, 4 Tern hatches can’t be 2 lbs, you’ll need a MaxxFan for ventilation or something similar
You haven’t accounted for plumbing and wire and power distribution.
Account for fuel and tanks for heat system.
only 5 lbs for tools? and no recovery gear?

this is a start

Good feedback here!

I definitely did NOT account for fastgun turnbuckles, and should have. The tank weights are probably low, too, and I also forgot to add the fan vent. Good catches!

I feel goodish about the habitat shell weight. The exterior would be 1/4", with a 1/8" internal skin, and XPS is pretty light, too. I used some online calculators to get approximate weights for those things.

The flatbed weight came directly off of Duramag's website, but you're right, boxes would definitely add more weight.

I sadly have no numbers for the door/hatches, because the Tern website for some reason doesn't publish that info (they do for their windows, though!) I guessed, clearly poorly!

As for recovery gear, I'll probably toss some maxx traxx and a shovel in there. I'm not going to be offroading, so I'm not really worried about having a winch or anything. The toolbag I carry with us in our trailer is about 5lbs currently.

But point noted: this list is almost certainly under-estimating the weight. Which means the F-350/3500 SRW is almost certainly NOT up-to-the-task even at max available payload.

Which means I need to go back to looking at DRW variants or F-550/5500's.

 

[ReluctantTraveler]

Regarding the F-550/5500 class trucks...

I'm realizing a big part of my challenge in finding trucks has been that my design called for a very specific truck:

1. Crew Cab (family of 4).
2. 4WD (no off-roading planned, but I live in snow country and want to use it as a snowboard home base and maybe even take it on a beach if possible).
3. Extra-long wheelbase, because I wanted to maximize the habitat size.

Of these three criteria, item 1 + 3 seems to be the hard-to-find combo.

I can find plenty of crew cabs, and a good amount of standard cab long wheelbase F-550's. Finding them together has been damn near impossible unless I'm ok with a rig with 150k+ miles on it.

If I can make the shorter wheelbase work (and clearly I can since I'm looking at F-350's), then it gets a lot more viable.

 

[mog]

I've been running a bunch of numbers on both a Total Composites build and a DIY habitat (using wood framing and XPS insulation similar to what @IdaSHO did).

Perhaps you could give a synopsis of your build plans so it is not necessary to read 15 years of @IdaSHO posts.
It looks like from your materials list you are planning an (unknown size) habitat with 1/4" plywood sheets on the outside, framed with (unknown size) wood 'studs' with (unknown thickness) foam and 1/8" plywood sheets on the inside. No FRP sheeting, inside or out, correct?

 

[calameda]

So you are laminating the foam panels w marine ply I guess? That will need some not insubstantial coating (more than just paint) to be weather resistant, so that’s more weight. What about the framing and corners? Going to reinforce those w alum angle or something? More weight.

I don’t go “off-road” either, but often on FS and BLM roads and manage to get stuck fairly regularly (4x last year) usually in mud. If you’re often without a truck partner, think hard about a winch. Also a jack, hilift or similar. And even if you don’t expand your tool chest, at least get a patch kit and learn correct use. Has saved my bacon many times.

People have different opinions about SRW vs DRW, but DRW can substantially limit the roads you can go on. That goes for the width and height of your camper too.

Oh and even if you dont raise the truck, at least consider larger wheels, like 35s if they fit without modding, for better clearance and flotation. Oh, and you should get an air compressor if you want to go in sand, or adjust pressure for washboard. And to inflate a fixed flat.

The weight of all this stuff adds up quick.

 

[jk6661]

Scott and one of his guests discussed this very thing on an EP podcast. They said no more than 80 percent of GVWR.