I think a good standard would be scale weights that would let the owner know where the weight is distributed on the trailer frame. For example, a 10,000# fifth wheel would produce 20% pin weight, 2000#, leaving 8000# to be distributed to the axles. When loading a trailer too much towards the rear, this causes sway (just a known fact), too much in the front may overload the pin, or tow vehicle. These weights can be found when weighing each axle seperately. I like to watch my axle weights more than pin weight but do keep my pin weight in check. I am not quite at 20%, probably 18%, but have towed for years and the "seat of the pants" feel lets me know when things are not loaded correctly.

Frame Flex I think is more towards the larger fifth wheels and toy haulers where they can easily get overloaded with all of the storage and/or toys in the rear garage area. This would cause a more severe motion in the pin box area at road transitions, dips in the road where the truck and trailer are going up and down at different times. With the smaller and/or lighter fifth wheels this would be less dramatic, thinking anything less than 15,000# or so.

I have not seen any published stats on Lippert frames. I think that all RV manufacturers send their plans and weights to Lippert and Lippert designs the frame to meet what the manufactures need.

All trailer frames need to flex in some manner. Watch a flat tow behind trailer or gooseneck trailer traveling down the road with some manner of load aboard. You can see them move and flex when road bumps are involved. Now with that same frame put a house on top and the flex and movement become magnified because of the 8' tall walls that the eye can plainly see moving, not too noticeable on bare trailer frame.

All that said it does concern me but not too much as my trailer only weighs 11,000# at gross max, less than that for our use, but I do keep an eye on side walls and pin box area for potential issues. I would be more concerned with a larger or heavier trailer, again around the 15k# area and above.

We also have to remember that since the 1900's we have wanted more out of campers, larger bath rooms, larger bedrooms, larger kitchens, more storage, better fixtures, home grade counter tops, and by the way make a garage on the back that I can take my smart car with me where ever I go. With all of that we want to keep the price and weight down so we do not need a semi tractor to pull it.

Brian

I scale before each trip and have always been under max TV payload by 250 or more lbs and GVWR of RV by 2300lbs. I am very heavy on the pin because of the factory Genset and W/D in the nose. Frame flex will be checked at the factory in a couple of months. Since I have some signs of abnormal flexing up front, I've tried to find out a spec from GD or LCI but come up empty. Don't rely on the YT videos because the amount of allowable flex seems to be different on each video. But, I'll attach LCIs upper deck flex form but note that they don't specify any max values.

Grand Design issued a Technical Service Bulletin - 24-001 on the upper deck flex inspection. This is for Momentum & Solitude Yeas 2021, 2022 & 2023.

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Anyone have a copy?

It was released to dealers this week, and I’ve seen it but don’t have permission to post it yet. It contains instructions to measure for excessive frame flex, but fair warning the process is meant for tech’s and isn’t owner friendly. If I get permission I’ll post it.

Is it the same as the Lippert upper deck measurement form?

It is not.

Thanks Neil. Just got off the phone with GD and they are still holding it internally because there are a lot of human resources working the issue still. One thing they did confirm to me is that there has not been one catastrophic failure in transit addressing my concern to tow to Elkhart in a month. I do find it interesting that allegedly it impacts 2021, 2022, 2023 model years which may imply a change in frame spec to LCI?

I can’t speak to the date issue, but what you were told regarding any issues in transit is what we were told as well.

The years of impact makes sense to me because of the three year limited warranty on the frame, but this is just a guess on my part. When I read the TSB if the measurement is 3/8" or less replacement of lag bolts is done. If the measurement is 3/8" or more call grand design customer service for further instructions.

Interesting. This is the same measurement for the same flex that I was given through a TSB back in the early 2000's for the same issue with my 2005 trailer. Actually it was 10mm, but if the TSB was sent to a Canadian dealer right now it would likely say 10mm instead of 3/8. So this issue has been going on for at least 20 years. Still a concern of course to those that have excessive deflection, but I find it amazing that Lippert discovered the issue so long ago and still hasn't successfully dealt with it and eliminated the weakness from their designs.
This isn't really a GD issue..it's a Lippert issue, but it says GD on the outside so I guess they get the calls.

I believe that was the same number I was given on the phone by LCI when they sent me their upper deck flex measurement form. I'll be interested in reading the GD TSB when I can get a copy. I'd like to look at it before heading to Elkhart.

I'm retired now but when I use to work we did Accelerated Life & Stress Testing (HALT/HASS). If there were changes in the systems we delivered we would have to preform the test again to ensure we did not reduce life expectancy. I'm not sure if the RV industry does the same thing. My guess is no due to budget constraints.

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I don't see how they can since some heavy options are either dealer installed or can be dealer installed. Washer/Dryer in our case was dealer installed and that added over 200lbs right on the nose and all on the door side. And none of their weights assumed travel with anything in the tanks which allegedly are empty when GD weighs for the placard. However, I was told that when GD weighs the rig it is right after plumbing and tank leak tests and the tanks are not always fully emptied. I catalogued placard weights on about 10 310GKs prior to ordering - same delivery options and the placard weight varied by hundreds of lbs. During COVID, the dealer installed a number of options that the factory either couldn't source or didn't have the production staff to do the work.