What makes up a GVWR rating?

Thanks Ron!

Yes, I resized to 480 x 640. Followed the same process as the first two. Will have to try this again.

It worked for me. Did you use the 480 and 640 limits for each image?

I don't think there's a limit on number of images in a post -- at least not as low as five.

I cannot get the final two photos embedded into a post. I just get an outline of a large box with a small symbol in the center. Worked fine for the above two photos. How can I fix this? Also, is there a limit to the number of photos in a post?

Thanks!

myredracer wrote:
---In any other industry I can think of, from building construction to automobiles, there are various standards spelling out how things must be done and anyone would have access to them. So - there are none in the RV industry? And a frame manufacturer can design and build to their own specs?? I also wonder what quality control methods they actually do have in place.

I think the closest you will come to that information would be found in the various standards which have been adopted by the Recreation Vehicle Industry Association.

Unfortunately most of their information is proprietary. But, it is available for purchase by non-members.

I doubt their standards go into much detail regarding the questions you've raised. I'm guessing most of that is left up to the individual manufacturers.

Ron

Ron,

The tires are 4 x 1820 lbs = 7280 lbs. The axles are 2 x 3500 lbs. The GVWR is 6800 lbs. Actual tongue weight is 960 and trailer weighs 6600 lbs. leaving 5640 lbs directly on the axles. A 6800 lb assigned figure makes sense, I guess. Tires are Freestar and don't know how long they will last before they explode. They seem close to the GVWR, but then the actual weight on the axles is under 6K lbs.

I am really wondering from a technical materials and construction detail perspective what gives a frame its strength and GVWR. Obviously, axle rating is one factor. But what metal thickness, beam height, flange width, and frame length affect GVWR ratings? What about spring hanger brackets and spring strength? What about cross-bracing from left to right side, and what spacing should they be on? What about weld details? Are welds continuous for the entire length of the joint or are they stitched together in only a couple of sides? What about the A-frame and also how it attaches to the I-beams? What about the grade of steel used? Is the frame strengthened where the tanks are? In any other industry I can think of, from building construction to automobiles, there are various standards spelling out how things must be done and anyone would have access to them. So - there are none in the RV industry? And a frame manufacturer can design and build to their own specs?? I also wonder what quality control methods they actually do have in place.

myredracer wrote:
ps: how can I embed photos directly into a post?

When you are creating a post or posting a reply, to embed a photo image:

First go to Photobucket and find the photo which you want to embed.
In the box titled "Links to share this post", click on the window titled "Direct" The window will briefly say, "copied".

Then return to your posting page and click on the icon which looks like a post card with a yellow background -- it is fifth from the rigt and is titled "Image" when you place the cursor on it. That will open a window with two boxes.

Paste the copied URL into the box titled "Enter the complete URL for the image".
It's always a good idea to enter480 in the "Height" box and 640 in the "Width" box to limit the photo size on the screen.
When you click on "Finished", your image-generating text should show in the post you are composing.

Then click on the "Preview" icon to see a preview of your post with the image displayed

Here's your first image: Let me know if you have questions.

Gil, there are many ways of establishing a trailer's GVWR.

Just from looking at manufacturer brochure numbers, is seems that some of the possibilities are:

GVWR = the sum of the ratings for each axle.

GVWR = the sum of the ratings for each axle plus an assumed addition for tongue weight.

GVWR = the sum of the load capacities for each tire.

GVWR = the sum of the load capacities for each tire plus an assumed addition for tongue weight.

GVWR = the maximum load which can be carried without exceeding the allowable stress at any point in the frame or suspension system.

In the first post, you mentioned having two 3500# axles. Based on the first two "methods", that should give you a GVWR of at least 7000#.

Have you looked at the DOT (assuming you have US-rated tires) "MAX LOAD" rating for the trailer tires? Multiplying that value by 4 would give another indication of possible GVWR.

Assuming each tire can carry more than 1700#, then it seems likely that KZ has performed a frame strength analysis and used that as the basis for establishing GVWR.

The KZ Spree Specifications Page shows 23 models -- all with 15" tires. There are nine GVWRs ranging from 6000# to 9500#. One model shows a GVWR of 7900# and three show 7950#.

If they really do have GVWRs which differ only by 50#, that does seem to increase the likelihood the GVWRs are based on frame strength.

But, that's just speculation on my part.

Ron

20 years ago (or so) they used to have inspection stations everywhere in the province and every 2 years (IIRC) you had to take your vehicle to get inspected. They were very picky and could make you correct the smallest of things. I once had a modified car that was lowered which made the headlights a tad too low. I had to return it to stock height to get passed. (Shh- I installed the original springs just to pass and then put the ones I wanted back in. I was in my early 20s...) I don't recall ever seeing RVs there but that was sooo long ago.

There is no mandatory weight inspection now but they do have random inspections by CVSE in various locations. Mostly dump trucks and semis, but I do seem to recall the odd pickup truck and TT or 5th.

I just got to setting up to post pictures. Here are a few from the frame shop that inspected our frame. I don't recall if I have mentioned a failed aluminum weld in the framing. While adding some storage space in the pass-through, I discovered that a weld in a horizontal aluminum framing member has failed and separated from the alum. member the runs vertically. This weld is at the very front of the trailer on the right hand side, just below floor level, and directly behind the fiberglass cap. Now that I know about the extreme frame flex, I am making an educated guess that the frame flex has been causing the entire trailer structure to flex, thus causing the weld in the framing members to separate. The weld was likely not great to start with, which is possibly a contributing factor. I have to wonder if there are any other failed alum. welds hidden behind the inside and outsside skins. It's my understanding that welds should be continuous around the complete length where the pieces connect, not just a blob of weld on one or two sides. Again, I wonder what standards there are in the RV industry for welding?

Wheels way off camber when trailer pushed to the side.

Left side of trailer showing bracket bent in one direction.

Right side bracket bent in opposite direction compared to bracket on lfet side of trailer.

Distorted lower flange of I-beam due to extreme frame flex. Only towed about 100 miles so far by us.

Failed/separated weld in aluminum framing at front of trailer.

ps: how can I embed photos directly into a post?

beemerphile1,

Being an engineer and having worked with many structural and mechanical engineers, I would have thought that it was something technical and mathematical involving detailed analysis of the many components that determined GVWR. Boy, was I ever wrong!:S

Our frame is sooo elastic, as if made from rubber, it must have the last step with the secretary that got it way off. Double doh!! :S:S