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Old 09-20-2017, 03:05 PM   #1
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Trying to understand GVWR

Have had our TT for about two years. After I first bought it, I asked the service manager at the dealer I bought the trailer from, where they took the trailers, 5th wheels etc. to have them weighed. He told me with a straight face, they don't weigh anything.
Since then, I've asked many fellow campers I've met at various campgrounds if they weighed their rigs and if so, where? I was surprised that over half of them said they have never weighed their rigs. Of the ones that had weighed their rigs, most said the CAT scales.
I've read on several forums that weighing is essential to insure that one doesn't overload a unit because that could cause handling problems or a failure in suspension, structure or tires.
So, upon leaving on my last camping trip, I finally decided to have my rig weighed. On the day before departure I took my tow vehicle to the CAT scales with a full tank of gas, DW and myself plus most of the things we carry in the vehicle when we travel (we were minus our two 8 and 10 lb dogs but I figured we could add their weights in later)
On the day of departure, we loaded up and headed to the CAT scales again (because it was less than 24 hours since the last weigh, this qualified as a reweigh). I didn't have time to do two weighs so I only did the one with the WDH bars installed.
Ok, so here is where I am getting a bit confused.
Comparing actual weights (TT hooked up to TV) to the manufacture's specs, I have the following data:
1. TV front axle, I'm 400 lbs under the max
2. TV rear axle, I'm 280 lbs under the max
3. GVWR for TV I'm 900 lbs under
4. GCWR for hooked up rig I'm 2,600 lbs under
5. Towing capacity for TV I'm 2000 lbs under.
Here's where my confusion comes in:
The TT has a GVWR OF 6000 lbs.
The scales say that the weight on the axles of the TT is 5540 lbs. BUT, I've read somewhere that the GVWR for the TT Should include the weight that is being transferred into the TV via. the WDH. if that's true, I'm about 200 lbs over the 6000 lbs even though the weight on the axles is less than that..
What I don't know is how the GVWR for the TT IS calculated in the first place. Is it based on tire capabilities, suspension, trailer frame or ????
I have replaced the original C load rating tires with D load rated tires.
I guess what I would like to know is, what is the proper way to determine GVWR? Do I need to shed 200 lbs from the TT? Or what other options do I have?
Thanks for any comments.
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Old 09-20-2017, 04:03 PM   #2
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One thing you didn't do ( I think) is weigh you TV by itself. That way you can see how much hitch weight is being transferred to you TV. Without doing that you have no way of knowing how much your TT weights loaded. My guess also is your TT axles are rated for 3k or 3,500 lb. each is that correct?
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Old 09-20-2017, 06:47 PM   #3
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I'd recheck those numbers. You have the axles being within 680# of their max but the TV 900# under. The GVWR will always be under the the sum of the two axle ratings. Typically by a lot.
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Old 09-20-2017, 09:30 PM   #4
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Quote:
Originally Posted by MTK46 View Post
One thing you didn't do ( I think) is weigh you TV by itself. That way you can see how much hitch weight is being transferred to you TV. Without doing that you have no way of knowing how much your TT weights loaded. My guess also is your TT axles are rated for 3k or 3,500 lb. each is that correct?
The CAT scale I went to did not want me tying up the scales by disconnecting the TT. Thanks for the thought though.
As far as what my axles are rated for, I have not been able to find that data. The manufacturer of the trailer does not offer that information.
I would think I would be able to determine how much load was being transferred into the TV by subtracting the known weight on both axels without the trailer from the known weight on both axles with the trailer hooked up.
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Old 09-20-2017, 09:39 PM   #5
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Originally Posted by Hutch1954 View Post
I'd recheck those numbers. You have the axles being within 680# of their max but the TV 900# under. The GVWR will always be under the the sum of the two axle ratings. Typically by a lot.
You are correct. I do have some erroneous numbers listed. The 900 lbs under for the TV GVWR should have been 180 lbs. Also, the 280 lbs under shown for the rear axle should also be 180 lbs.
Sorry for the incorrect information.

In looking at the numbers a second time, I'm convinced that while my TV is capable of towing my TT, I have very little margin.
Time to trade both for something bigger.
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Old 09-20-2017, 09:40 PM   #6
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Most TT GVWR is calculated by the axle ratings + 10% on the tongue.

So a dual axle TT with two 3500# axles would have a GVWR of 7700#.

When I had a TT I always replaced the original tires with higher weight rating tires, and if I could, 14" wheels with 15" wheels. I didn't want the tires to be anywhere near the weak link.
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Old 09-21-2017, 01:11 PM   #7
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Originally Posted by tfryman View Post
Most TT GVWR is calculated by the axle ratings + 10% on the tongue.

So a dual axle TT with two 3500# axles would have a GVWR of 7700.
I crawled under my TT to see if the axles had some kind of identification.
I found a label on each on that said GAWR 3500 lbs.
So, I agree with you, one would think that the GVWR for the trailer the axles were used on should be 7000 lbs.
But, the data published for my model of TT clearly says GVWR 6000 lbs.
If it were 7000 lbs I would not have any problem.
I've inquired to the manufacturer about how the GVWR was established, but have not received an answer and doubt I will receive one.
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Old 09-21-2017, 01:51 PM   #8
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Tire rating will probably be >> less than the axle ratings.
See what the max rating for the tires is.
Probably explains the difference. (?)
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Old 09-21-2017, 02:04 PM   #9
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Tire rating will probably be >> less than the axle ratings.
See what the max rating for the tires is.
Probably explains the difference. (?)
Yep, if they cheaped out on tires, they would be the limiting factor. I bet your tires have a max carry capacity of 1356 Lbs each.
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Old 09-21-2017, 02:56 PM   #10
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Originally Posted by Twilightzone View Post
Tire rating will probably be >> less than the axle ratings.
See what the max rating for the tires is.
Probably explains the difference. (?)
Original tires were rated at 1750 ea or 7000 lbs total.
The ones I replaced them with are rated at 2040 lbs ea.
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Old 09-21-2017, 09:03 PM   #11
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Your trailer has a federal vehicle certification label located on the LH FWD external section of the trailer. There will probably be a tire placard along side of it. That certification label displays the trailerís GVWR, all GAWR values, tire sizes installed at the time of first sale and the recommended cold inflation pressures for those tires.

The GAWR values on the certification label may not match the values on the axle's individual tag from the axle manufacturer. Thatís because the trailer manufacturer gets to set the maximum GAWR values.

There are specific ways to get all the individual weights for your trailer at some scales. In the last few pages of chapter #4 of the reference below, you will find all the information needed to get all the weights you desire.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf

Note: Tires fitted to any RV trailer must have a load capacity equal to or greater than the GAWR ratings on the certification label.
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Old 09-21-2017, 09:16 PM   #12
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Originally Posted by FastEagle View Post

The GAWR values on the certification label may not match the values on the axle's individual tag from the axle manufacturer. Thatís because the trailer manufacturer gets to set the maximum GAWR values.
I'm beginning to see this. In looking at a the specifications for a similar model trailer from the same manufacturer, the other model is 2 feet longer than my TT but it has a 7000 lb GVWR.
Unless there are major differences in the structure of the trailer frames, I can see no reason why one model is rated 1000 lbs higher than a comparable model.

I've specifically asked about these differences to the manufacturer. Whether I get an answer or not remains to be seen. If I do get an answer, I will certainly post it here.
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Old 09-22-2017, 01:44 AM   #13
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Trailer GVWR is set by the MFG and are loosely related to the axle wt ratings since the GVWR also includes the hitch wt. Hitch WT. is usually between 10 and 15% of the total wt. A rule of thumb is to see what the dry hitch wt is as a % of the total dry wt. - or just use 10%. So a TT with a GVWR of 6000 lbs would carry 600 of those lbs on the tongue and 5400 lbs on the axles. So the mfg can use 1350 lb rated wheels and tires and 3500 lb axles. If they want to increase the GVWR to say 7700 lbs they would only have to change the wheels and tires to the next load range or 1750 lbs.


As for your truck - similar things apply however you will find that the GVWR is lower than the sum of the GAWRs. The object is to not exceed the GVWR first, then look at the GAWRs. But prior to all of that is the CGWR which is the maximum wt. for the truck and trailer plus passengers and cargo.


WT distribution bars apply torsion to the hitch point and shifts some for the hitch wt to the trailer axles and the front TV axle. Which is why you don't want to weigh with them attached if you want to get you true tongue and axle wts. To figure your weights go over the scales without the WD bars - get all 4 axle wts (if you can get the individual tt axles) Then go back with just the truck and get the front and rear axle wt. Simple subtraction will result in you tongue wt. You will also get your GVWRs for both the Truck and trailer.


Good Luck
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Old 09-22-2017, 04:31 AM   #14
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Quote:
Originally Posted by Randy the sly old fox View Post
Trailer GVWR is set by the MFG and are loosely related to the axle wt ratings since the GVWR also includes the hitch wt. Hitch WT. is usually between 10 and 15% of the total wt. A rule of thumb is to see what the dry hitch wt is as a % of the total dry wt. - or just use 10%. So a TT with a GVWR of 6000 lbs would carry 600 of those lbs on the tongue and 5400 lbs on the axles. So the mfg can use 1350 lb rated wheels and tires and 3500 lb axles. That's not true, the RV trailer manufacturer MUST use tires that will provide a load capacity equal to the Certified GAWR). If they want to increase the GVWR to say 7700 lbs they would only have to change the wheels and tires to the next load range or 1750 lbs.


As for your truck - similar things apply however you will find that the GVWR is lower than the sum of the GAWRs. The object is to not exceed the GVWR first, then look at the GAWRs. But prior to all of that is the CGWR which is the maximum wt. for the truck and trailer plus passengers and cargo.

(That's because the standard for automotive vehicles differ in the way they provide load capacity reserves. None are required for RV trailer tire fitments).


WT distribution bars apply torsion to the hitch point and shifts some for the hitch wt to the trailer axles and the front TV axle. Which is why you don't want to weigh with them attached if you want to get you true tongue and axle wts. To figure your weights go over the scales without the WD bars - get all 4 axle wts (if you can get the individual tt axles) Then go back with just the truck and get the front and rear axle wt. Simple subtraction will result in you tongue wt. You will also get your GVWRs for both the Truck and trailer.


Good Luck
According to the FMVSS standards for RV trailers the trailer's hitch/pin weights are an integral part of the vehicle manufacturer's equation for establishing a marriage for GVWR & total GAWR. The paragraph reads like this - in part - "The manufacturer's recommended hitch weight when added to the total GAWR must equal or exceed GVWR.
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