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Old 05-24-2016, 09:31 AM   #1
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Gross vehicle weight rating (GVWR) considerations

There is not an existing thread devoted exclusively to gross vehicle weight rating (GVWR) issues and so I thought I would plant one for reference. It was mentioned in passing in 56 other threads, but without a full discussion of what it means or how to determine an Interstate’s weight so that it can be compared to the published GVWR for that model.

First, the definition. Wiki says the following, which is consistent with other sources:

"The gross vehicle weight rating (GVWR), or gross vehicle mass (GVM) is the maximum operating weight/mass of a vehicle as specified by the manufacturer including the vehicle's chassis, body, engine, engine fluids, fuel, accessories, driver, passengers and cargo but excluding that of any trailers."

^^ The caveat with that definition is that tongue weight is not mentioned. This gets a bit confusing but the Interstate Owner’s Manual expounds as follows:

-- Gross Vehicle Weight Rating (GVWR) is the maximum permissible weight of the motorhome.
-- Gross Vehicle Weight (GVW): comprises weight of vehicle including fuel, tools, spare tire, installed accessories, passengers, cargo, and trailer tongue. It must never exceed the GVWR.
-- Gross Axle Weight Rating (GAWR) is a maximum permissible axle weight.
-- Gross Trailer Weight (GTW) is a maximum permissible trailer weight to be towed.
-- Trailer Tongue Weight Rating (TWR) is the maximum permissible weight of the trailer tongue.

So the way I read that by virtue of the bolded portion, GVWR effectively includes the tongue weight even if most standalone definitions don’t state that explicitly.

I don’t know how much GVWR potentially places limitations on owners of newer NCV3 Interstates with their larger size and extra pair of wheels, but it is very much a consideration for T1N-based Interstate owners. The basic predicament is this: By the time Airstream installed all that build onto the Sprinter, they were already running close to the GVWR. That’s before any passengers or typical cargo were added. Airstream was aware of this and made a statement that I find a bit defensive and even mildly condescending in the 2007 Owner’s Manual: "Do you really want to carry 300 pounds of water to a RV park 1,000 miles away and then hook up to a city water supply? Even if you’re going to the “boondocks”, you can usually fill your water tank shortly before entering the area. Just reducing your load by 10 gallons of water lets you carry an awful lot of fishing and camping gear." (page B-1).

My husband and I have made modifications to our 2007 Interstate, most notably an 88-pound solar system and some Dynamat noise dampening material (very heavy stuff), and we plan to make more modifications, including the addition of some kind of robust hitch carrier. For this reason we decided to go ahead and get some weight numbers to see where we were in relation to the GVWR for our model. We only have so much margin to work with, and we want to apportion it optimally.

We used the provider named CAT Scale because they are common and convenient (about two dozen in the greater Houston area). My husband set up a payment account using his iPhone. He described this as a time-consuming process involving the establishment of more than one password, so it’s best to do that in advance, especially if you are in an area of high demand because you’ll have big rig drivers on the clock, queued up for the scale, and breathing down your neck. Once that account was active, we drove to the scale and did two weighings – first the total, putting one pair of Interstate wheels on each portion of the scale front and back. Then we got off, circled around and did left and right, putting the driver’s side wheels on the edge and the passenger side wheels on the scale. The edge was flush with the scale and so that reading should be accurate.

The annotated screengrab below shows our total result. This represented a moderate T1N Interstate loading scenario which included the fuel tank being about 75% full and the fresh water tank 67% full, two adults, one dog, and gear for a short trip.

The published GVWR is the same for all four 2007 Interstate models – 8,550 pounds - so you can see that we were 430 pounds under the GVWR. That’s not much leeway – it’s the equivalent of about two large additional adults (with six seatbelts in our Interstate, I like to joke that, if we had a full load of fat butts onboard, we might already be at GVWR before a single can of Coke is even placed in the refrigerator). It’s enough to work with, but again, we can’t go piling on improvements indefinitely and remain under the GVWR, so we have to be mindful of each additional thing we do.

FWIW. Perhaps someone else could provide perspective as to how this issue might impact NCV3 Interstate owners -- or perhaps it does not pose analogous limitations, if they have a larger margin to work with.
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Old 05-24-2016, 09:44 AM   #2
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This gets a bit confusing but the Interstate Owner’s Manual expounds as follows:

-- Gross Vehicle Weight Rating (GVWR) is the maximum permissible weight of the motorhome.
-- Gross Vehicle Weight (GVW): comprises weight of vehicle including fuel, tools, spare tire, installed accessories, passengers, cargo, and trailer tongue. It must never exceed the GVWR.
-- Gross Axle Weight Rating (GAWR) is a maximum permissible axle weight.
-- Gross Trailer Weight (GTW) is a maximum permissible trailer weight to be towed.
-- Trailer Tongue Weight Rating (TWR) is the maximum permissible weight of the trailer tongue.

So the way I read that by virtue of the bolded portion, GVWR effectively includes the tongue weight even if most standalone definitions don’t state that explicitly.
You are quite correct in your interpretation. Any weight added to the hitch receiver is part of the gross vehicle weight and rear axle weight.

Since you've made such extensive modifications to your solar setup, you might gain extra capacity by permanently removing the generator. Between shore power, robust solar, and your engine alternator, the generator is pretty much just 125 pounds of ballast at this point. There are very few scenarios where you'll ever need to run it again except to exercise it.

On edit— If you ditch the generator but keep the mounting brackets, you could add a concealed storage box where the generator used to be, for stuff that you want to protect from being stolen out of the hitch-mounted box.
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Old 05-24-2016, 09:57 AM   #3
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Looks like if you start out w/ a full tank of fuel, propane, and water, you'll already be at or over GVWR before you climb aboard w/ luggage, etc.
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Old 05-24-2016, 10:49 AM   #4
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As a postscript, of course T1N Interstates are not the only vehicles that run up against weight considerations. I adore these drone shots that occasionally appear on Insta. We can talk and talk about total weight and what to take and not take in view of the limitations, but a picture tells a thousand words. First Interstate owner to post their visual inventory thusly gets lunch on me if we ever find ourselves in the same location.
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Old 05-24-2016, 11:08 AM   #5
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Since you've made such extensive modifications to your solar setup, you might gain extra capacity by permanently removing the generator. Between shore power, robust solar, and your engine alternator, the generator is pretty much just 125 pounds of ballast at this point. There are very few scenarios where you'll ever need to run it again except to exercise it.
Correct, and we are considering it, except that the one scenario where we might need it is a real killer - caught unexpectedly in the middle of nowhere or in a disaster area during a heat wave.

Having lived through both Ike and Rita, and having seen other people do the same, we've learned that even one to two hours of air conditioning per each 24 hour period can provide a tremendous restoration to the body, seemingly out of proportion to the duration of the benefit. And we can't run a/c with solar. And our chances of still owning this Interstate at the point of our next hurricane evacuation are somewhere close to 100%. If we can scrounge up shore power, no issue. But we could not during the most recent two evacuations. Hell, after Rita, many City of Houston locations (including ours) lost water pressure. Electricity was a distant dream after Ike, and some people remained without it for as long as three weeks.
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Old 05-24-2016, 11:18 AM   #6
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That's the reason AS moved to the one ton chassis in the newer Interstates. More gross weight.
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Old 05-24-2016, 11:23 AM   #7
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That's the reason AS moved to the one ton chassis in the newer Interstates. More gross weight.
My husband says the same thing but in fact, T1N production ceased after 2006 and so Airstream wouldn't have had a choice either way. It was NCV3 or nothing.
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Old 05-24-2016, 11:28 AM   #8
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All I know is pre 07 you could buy each size sprinter but AS chose the three quarter ton. Could be wrong. After 06 it appears only the new version was available.
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Old 05-24-2016, 11:43 AM   #9
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Correct, and we are considering it, except that the one scenario where we might need it is a real killer - caught unexpectedly in the middle of nowhere or in a disaster area during a heat wave.
You could still remove that 125-pound beastie and replace it with a smaller and lighter— and quieter— portable generator (Honda or Yamaka 2kW) carried in the cargo box for those trips when you think you might need one and left at home when you don't think it's required. Plus when you do need a generator the portable could be set up 20 feet away at the end of your shore power cord where the sound is a lot less obtrusive to you.
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Old 05-24-2016, 12:00 PM   #10
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All I know is pre 07 you could buy each size sprinter but AS chose the three quarter ton. Could be wrong. After 06 it appears only the new version was available.
I'm not doubting you, but for the sake of curiosity, could you point me in the direction of a reference? When I look up data for the 2006 Sprinter model year, what I see as having been available in the U.S. are the 118 WB (standard and high roof), 140 WB (ditto), and 158 WB, all being 2500s. The T1N Interstates were all built on 158 WB 2500 Sprinters - the largest. Of course, mixed in with the constant confusing replating changes were the chicken tax issues, so if there had been a larger-still T1N produced, I wonder what the availability was like?
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Old 05-24-2016, 12:50 PM   #11
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If we can scrounge up shore power, no issue. But we could not during the most recent two evacuations. Hell, after Rita, many City of Houston locations (including ours) lost water pressure. Electricity was a distant dream after Ike, and some people remained without it for as long as three weeks.
Just something to keep in mind, if you are planning on using the generator because the power is out, is that it will likely out at your nearby fuel station as well. You then need to plan on carrying sufficient fuel for those (x) weeks.

I used to work in a Chevron station in a rural area, with recurring power outages. It was amazing how, every time the power went out, local generator owners showed up at the station with their jerry cans, assuming the pumps would work.

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Old 05-24-2016, 01:36 PM   #12
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Our onboard Onan generator runs on propane. If we did replace with a standalone unit transported only when needed, it would have to be propane as well. This is a darned good idea, and not something I've looked into yet. Even when we lose electricity and water because of hurricanes, we tend not to lose gas service unless uprooted trees have damaged the local lines, but still it's less likely (I have vivid memories of helping to cook food for nine local "refugees" on a residential gas cooktop right after Hurricane Rita). If I could ID a unit with an adapter or whatever that could run on both hard-piped natural gas and onboard propane, that would indeed be something to think about.
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Old 05-24-2016, 01:56 PM   #13
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There was a dual wheel sprinter available and it had fifteen inch wheels not sixteen. I think this was a one ton?
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Old 05-24-2016, 02:00 PM   #14
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I found info on the 3500 sprinter In 2006 on cars.com
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