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Old 04-27-2014, 06:55 PM   #1
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Does GVW include kingpin weight?

Just got back from a trip to the South West. Had a great time except for a tire blowout on the Interstate... no fun at all!!

So now I'm going over the weights to see if there's a problem I can fix or at least look out for...

I weighed the trailer and the truck and found that the truck is carrying about 700Kg (1543lb), the kingpin weight.

The GVW of the trailer is 4114Kg (9070lb) and I measured the axles are carrying 1600Kg (3527Lb) each. If I add the axle weights 3200Kg (7054lb) and the weight on the kingpin of 700Kg, I get 3900Kg (8598lb)...

The max GVW of the trailer says 4114Kg (9069lb) which would mean I could only carry 214Kg (472lb).

If I don't include the kingpin weight it would give me an extra 700Kg of cargo capacity.

When I measured the weight it was with a full fresh water tank, a full water heater and full propane tanks.

So, there's the question, should I include the kingpin weight to find GVW or not?

I am very disappointed with this tire blowout. This is our 3rd fifthwheel trailer and the only one we've ever had this problem with. In my opinion the axles and the tires are not heavy duty enough to take the weight of the trailer. Perhaps they are OK with a trailer that has no options, but ours has the "diamond" package which adds weight.
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Old 04-27-2014, 06:59 PM   #2
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The trailers GVWR includes the king pin weight. You'll likely have 4,000 pound axles under your unit. Generally the manufacturers determine GVWR by taking axle capacity + dry pin weight.
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Old 04-27-2014, 07:15 PM   #3
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Just a thought? Why do you carry the water while towing? I stop a the entrance to fill up, if theirs not available water at the site....
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Old 04-27-2014, 07:27 PM   #4
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Sticky question actually.

The axle ratings are derived from GVW minus pin weight. So a 10,000lb GVW trailer with a 1,000lb pin weight would need axles capable of carrying 9,000lbs, or dual 4,500 axles.

So, the GVW is the entire thing pin weight and all, but the axles are chosen with the thought that some of that weight is transferring to the truck. For example, my trailer has dual 7,000lb axles, but has a 15,550GVWR. Way too much for the axles alone, but with a 2,500 pin weight it's actually 1,000lbs under axle rating.

I am still wondering, where in the world do you put the 4,500 payload this thing can carry.

What truck and trailer do you have?
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Old 04-27-2014, 07:28 PM   #5
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Quote:
Originally Posted by ependydad View Post
Generally the manufacturers determine GVWR by taking axle capacity + dry pin weight.
I had a long talk with the Lippert engineers at the rally concerning this very topic.

My camper has a GVWR of 9200 pounds and 4,000 pound axles. That would make the maximum king pin weight 1200 pounds to stay under all the limits.

Since the pin box is rated to 15,000 pounds, I asked what the GVWR would be if I upgraded to 5,000 pound axles.

The answer shocked me. With the upgraded axles the GVWR would still be 9200 pounds. The reason is the dynamic of calculating the GVWR is totally dependent on the lowest rating of any component.

Since when they design a camper body style and weight class in the blueprint stage, the structural engineers look at all the limits of all the individual components and find the lowest rated one in the mix. THAT becomes the GVWR. There is no way to tell (without doing another structural review) what the NEXT lowest rated it is in any design.

It could be the frame, but it could just as easily be the side wall structure. I was told that the next higher weight class (12,000 pounds) had many more aluminum structural tubes in the composite walls to prevent cracks at that higher gross weight.

Strengthening the axles may (MAY) add a few hundred pounds, but then again the odds are also (maybe not). Your first indication that your brand new axles were a bad idea might be sidewall cracks at the slide openings.

That conversation saved me a ton of money.

BTW my empty weight with almost no water is a bit over 8100 pounds giving me a gross cargo load of about 1000 pounds.

Can goods have gone the way of the dodo. We now pack stuff that comes in sacks as much as possible. Plastic has replaced glass and silverware; and my tool box has shrunk like crazy. Carrying the DW's dialysis supplies is going to REALLY challenge my packing abilities.
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Old 04-27-2014, 09:19 PM   #6
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I often carry a full fresh water tank because we like 'wild camping' (boondocking) where there are no hookups. We also stay, at times, in parking lots, ETC, so a full fresh water tank and empty holding tanks is a good idea. Even if I know where we're going to camp and I know there will be water there, I always keep some water in the fresh tank for those 'pit stops' on the road at rest areas, or where ever...

Hope that explains it.
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Old 04-27-2014, 09:49 PM   #7
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OK, so the GVWR of the trailer is the axles plus the kingpin.

For this trailer the GVWR is 4114Kg.
The total I measured was 1600Kg (axle 1) + 1600Kg (axle 2) + 700Kg (kingpin) = 3900Kg
4114Kg - 3900Kg = 214Kg
So, if I have a full tank of water I can carry 214Kg of other stuff! (I have to admit that the weights above do include some other things like pots and pans and dishes and some cloths, but not much)
So it looks like I'm going to have to be very careful about what I take!!!

BTW, there's a little sticker on the screen door that says:
Dry weight is 7507lb (3405Kg)
Cargo capacity is 1513lb (686Kg) <-- sounds like a lot!
Full tank of water is 308lb (139Kg)

So with a full tank of water it should weigh 3405Kg + 139Kg = 3544Kg
That's 356Kg less than what I measured, I can't see that I have 356Kg of 'other stuff', but maybe if I add the two propane bottles full, and ???

The numbers don't seem to add up... Sure would be nice if they gave me a bit more room to take things along. It would also be nice if they added a bit more safety margin to the tires, then maybe I wouldn't have had that wonderful experience of 18 wheelers flying past me at 75mph while I wait on the shoulder of the Interstate.

Maybe I'm just venting now!
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Old 04-28-2014, 07:14 AM   #8
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Your "full tank of water" may not be full.

Depending on that "attitude" of the camper at fill up and the location of the fill line and vent, and the probe location during install, you may have gotten less water than you think even though it gushes out the fill and vent lines.
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Old 04-28-2014, 12:29 PM   #9
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Originally Posted by SKnight View Post
Sticky question actually.

What truck and trailer do you have?

The trailer is a 2013 Rockwood 8280WS with the 'diamond' package and the truck is a 1999 Ford F250 super duty with a 6.8l V10

I believe I'm well within the weight carrying capacity of the truck. My only concern is that the trailer is carrying too much weight.
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Old 04-28-2014, 12:34 PM   #10
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Originally Posted by Herk7769 View Post
Your "full tank of water" may not be full.

Depending on that "attitude" of the camper at fill up and the location of the fill line and vent, and the probe location during install, you may have gotten less water than you think even though it gushes out the fill and vent lines.

Thanks for the reply... you are absolutely correct. I found that I have to be quite careful when I fill the tank if I want to get it all the way full... discovered that on one of the first dry camping adventures where we ran out of water really quick!! Next time I filled the tank a little slower and found I could put quite a bit more in it... I just keep filling until it comes out, but if I do that with the water going in too quickly the water comes out before it's actually full, so I have to slow the fill rate to get the last little bit in...
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