Undersized axles on Momentum 320G or just poor design?

[howson]

Moderator note: these posts were moved here from https://gdrvowners.com/forum/gdrv4li...mber-in-norcal The original posts are still in that thread, but it is closed so there's not a duplicate discussion happening on this topic. -Howard

New Member (July 2021) with a 2021 Momentum 320G. Added more solar, upgraded converter, added 300mAh Chins Lithium Battery. Carry 4 dirt bikes, family and gear most trips. Already have almost 2,500 miles on the rig. Love it, except for the horrible sway all over the highway I get. May need to upgrade Axles? and F350 to F450?

Love the layout and all the bells and whistles though! Looked at so many trailers before deciding and owning 4 Toy Haulers prior to this one.

Sway from a 5th wheel? That's unusual--or I'm just used to reading about travel trailer sway issues.

Have you gone across a CAT scale fully loaded to determine the pin weight? If not, well worth the time and effort to do so. It's the first step to solving the sway problem. If the pin weight is not around the 25% of the trailer's total weight, that could be the problem.

[chikenstiker]

PS: Dealer told me that my F350 SRW was more than enough and me looking at online specs and not the door tag has proven to be a learning event. Truck was overloaded by 800 lbs at the scales even with this light Pin Weight. Only had a tools, family of 4 , dogs and an Ice Chest in the truck.

I put Ice Chests in the back of the truck since the Garage can't handle them... LOL!

[TheNescios]

Couple of thoughts come to mind:
What is the weight like side to side on the trailer? For my 3740 bunkhouse it's 800# +/- heavier on the drivers side due to the 3 slides & kitchen on that side vs 1 slide on the passenger side the times I've checked.
What tires are you running? Hopefully a solid F rated 12 ply and preferably a G rated 14 ply
Assuming the basics of checking tire pressure and tire conditions have been checked numerous times by both yourself & the dealer - but a TPMS might be useful to see how the tires are doing when driving?
Only other thing that comes to mind is if there was some odd circumstance where the tires weren't tracking correctly - but it takes a place that specializes in trailer alignment to get accurate results.
If one side was just a small amount forward or backwards of where it was intended to be or if the front & rear weren't within a very small tolerance of each other I can see where it might result in what you're experiencing.
Hoping you find a cure for the sway soon and share what the issue was?
Chris

[howson]

Pin = 2,480; Axles = 14,340; Total = 16,820

GD's specs show a GVWR of 16.8K, so 25% for pin weight is 4.2K. The axles would then carry 12.6 which is within their rated spec. Something's not right if all you can manage is a 2,480 pin weight.

Out of curiosity, do you have baseline numbers (nothing in the camper)? How does it tow empty?

The truck...that could be (and has been many times on this forum)...an entirely separate discussion. Do a bit of searching in Towing and Hitches channel. There's also resources linked in that channel's Reference Material sub-channel.

Please keep the forum informed on what resolves the issue.

Howard

[ncitro]

RoyB Can I ask what you ended up doing with your trailer/truck situation? I am having the same issue as you with A LOT of sway on the highway and downhills. I've had the 320G to the dealer and GD had the measure a bunch of frame and axle dimensions which all came out correct, so they told me to tow without Water in the tank. I bought this expensive rid to camp in the middle of nowhere and bring dirt bikes. We don't wet camp, we're always in the sticks and it would be a great hassle to not carry water and then find a place at 10 PM at night on the way before we turn off the main roads and god forbid we need water a long the way for an emergency or bathroom break.

I feel like this is just a bad design and needs to come with 8000 lbs axles from the factory and debating if that upgrade would help?

Went camping last weekend with 3 dirt bikes in the back (usually I have 4 but ACL surgery so I'm down a few more months) and I moved as much weight as I could forward (Gear Bags in Front Bedroom, wheel chalks in Propane tank cubby) AND I brought some heavy steel targets so gimpy could shoot while family was out riding.

CAT Scales

Axles 14,340 (340 lbs over and that's a bike short of all other trips)
Pin 2,480
Pin Ration 14.7%

Trip was horrible on sway and white knuckled on 5,000' decent!

Dumped all water and Grey for ride and sway controllable, but still not what I'd expect from a 5th wheel and again that was with extra weight in the front and one bike missing.

So do I upgrade to an F450 and hope the extra Payload and Stability are enough? Do I sell this camper and go another route or back to a tow behind??? Decisions......

Side Note, I realize the truck is not enough now. I really thought an F-350 XLT was enough truck, but I was 800 lbs over Gross at the same time as not having enough pin weight....

I'd doubt your sway issue is due to being over the trailer axle weight. That may not be good for it in the long term but sway is mainly caused by the pin weight percentage. A dually might help, but you really want the pin weight on a fifth wheel up near 20-25% to eliminate sway. Out of curiosity do you know what your percentage is when you had the tanks empty and it towed a little better?

I'm surprised with that pin weight you're over the payload rating off the 350 XLT. I think my Platinum 350 has a payload of over 3k. Do you have a lot in the bed?

[Cate&Rob]

chikenstiker

I would agree with Neil that 5th wheel trailer sway is not likely related to trailer axle capacity. The tire and suspension (lift?) mods to your truck may have something to do with this. Your original payload should be in the 3400 lb range . . . so, should not be an issue unless your mods have reduced this.

Rob

[chikenstiker]

Cate&Rob ncitro howson Answering multiple questions.

From Factory Left Side 5632 Right Side 5322, not sure after being loaded, left side with kitchen and pantry may be a smidge more?

F350 Payload per sticker is 32xx lbs. So 2500 Pin plus 6-700 in people and dogs plus 100lbs in tools straps first aid, etc then 15 gallons of fuel in the bed for the dirt bikes, Ice Chest with drinks, then heavy duty sway bars and airlift kit and B&W hitch and we're well over that payload. I would imagine most families are, maybe a couple with light load is ok?

I don't think the trailer being 20 lbs over or the axles being over is the sway, it is definitely the Pin Weight, but the point is the trailer is at max with too light of a Pin and I can't move anymore weight forward. We already keep all gear bags in bedroom, BBQ and Propane tank in Pass through, extra drinks and stuff under bed. I even keep the ice chest in the truck since that 100lbs would hurt us in the Garage.

Ride home with less sway I did not hit the scales, but estimate my Pin weight was about 15.5% which is still low and I only had 3 of 4 dirt bikes this trip.

I think this trailers balance is just way way off for it's "intended" use!

RoyB messaged me back and he adds water to the Grey Tank every trip now, which means I'm wasting water in a drought and making my campsite muddy when I get there or making a stop at the dumps on the way in.

Thanks for everyone's input!

[chikenstiker]

PS. Trailer Tires are Cooper H Rated, whomever asked. I've run them 110, 115 and 120 PSI with no noticeable difference. Chart on web says 90 psi would carry the load?

[Guest]

Also agree your axles are not causing the sway. However, if the trailer could be equipped and approved for heavier axles, it may be possible to balance the load to put more weight over the trailer axles. Trailers inherently handle better with most weight over the axles. From there, axle placement will dictate tongue weight range under normal and approved loading.
Excessive TV tongue weight can raise the steer axle of the truck and cause sway through oversteer. Excessive rearward trailer weight can move the center of mass too far rearward and will also result in sway.
And a TV suspension modification can cause issues as well as large oversize tires that can exhibit a great deal of sidewall flex.

Oh and a larger heavier truck will always help. A heavy TV takes much more energy to horse around than a light one as compared to the trailer mass.

Hope you get this sorted out.

Jim

[Cate&Rob]

chikenstiker

Is your truck lifted? (to clear the 34" tires). If so, how close to level is the 5th wheel? If the trailer axles are not equally carrying the weight of the trailer (because the front of the trailer is high) this might be a factor.

Rob

[Hogdrv]

chikenstiker

I have the same trailer and my sticker says 125 psi with H rated Cooper tires . I have had a H-D Ultra in back but not full of fresh water but no sway, I’ll have to test it with full fresh water and see.

[chikenstiker]

Also agree your axles are not causing the sway. However, if the trailer could be equipped and approved for heavier axles, it may be possible to balance the load to put more weight over the trailer axles. Trailers inherently handle better with most weight over the axles. From there, axle placement will dictate tongue weight range under normal and approved loading.
Excessive TV tongue weight can raise the steer axle of the truck and cause sway through oversteer. Excessive rearward trailer weight can move the center of mass too far rearward and will also result in sway.
And a TV suspension modification can cause issues as well as large oversize tires that can exhibit a great deal of sidewall flex.

Oh and a larger heavier truck will always help. A heavy TV takes much more energy to horse around than a light one as compared to the trailer mass.

Hope you get this sorted out.

Jim

The scales showed that my TV Front Axles were 40 lbs heavier with the Fifth Wheel attached, so the front wasn't being unloaded in this case.

I want to see what GD says about the 8000 lbs axles and if they can help with the price since this is a known issue, the problem is that the Garage is behind the axles and at the Axles is my living room with dual slide outs so there isn't really any room to add or move weight there. I already only have dirt bikes and chairs in the garage and the other things most would are in my bedroom (boots, gear bags, etc.)

[chikenstiker]

chikenstiker

Is your truck lifted? (to clear the 34" tires). If so, how close to level is the 5th wheel? If the trailer axles are not equally carrying the weight of the trailer (because the front of the trailer is high) this might be a factor.

Rob

I only have a small leveling kit on the front of the truck. Tires are ~34" and I want to say stock were ~33 so only 1/2" taller at most in the back.

I have 5-6" of clearance to the bed rails, I can't go any less as when I'm pulling into some tight spots out in the woods I've just barely missed touching.

Front of the trailer is up slightly when hitched up and 60 lbs in the air bags, when I get to the dirt I usually let the air out of bags so truck squats more and then it's close to level, not quite.

[chikenstiker]

chikenstiker

I have the same trailer and my sticker says 125 psi with H rated Cooper tires . I have had a H-D Ultra in back but not full of fresh water but no sway, I’ll have to test it with full fresh water and see.

Interesting on the Tire PSI. I hadn't noticed the sticker. I got rig from dealer with 110 PSI in it, I tried 115 and didn't notice a difference, this last trip I put them at 120 PSI and had more sway than ever even though I think my Pin was heavier than normal?

I'll try 125 PSI next.

The rating on these tires per Cooper was like 87 PSI to hold 14,500 lbs or something like that.

How much does you Ultra weigh? I figure 4 dirt bikes and chairs and a few things to be ~1,000 lbs.

I do notice you have a DRW and wonder how much that helps?

Thanks everyone for your input!

[Hogdrv]

The Ultra weights about 900 lbs so about the same as your dirt bikes. Maybe the DRW helps don’t know?

[chikenstiker]

The Ultra weights about 900 lbs so about the same as your dirt bikes. Maybe the DRW helps don’t know?

So our only real differences are Water and DRW. I think I'm a little heavier other places with the family,but those weights on and in front of axles would only help me...

Be interesting to see how it did with water for you?

For options that add weight to rear, I have the 2nd awning, plus rear awning, plus patio deck kit and Happy Jack.

[Guest]

The scales showed that my TV Front Axles were 40 lbs heavier with the Fifth Wheel attached, so the front wasn't being unloaded in this case.

I want to see what GD says about the 8000 lbs axles and if they can help with the price since this is a known issue, the problem is that the Garage is behind the axles and at the Axles is my living room with dual slide outs so there isn't really any room to add or move weight there. I already only have dirt bikes and chairs in the garage and the other things most would are in my bedroom (boots, gear bags, etc.)

I'm thinking you should be seeing more than a 40lb increase on your front axle especially with family, and other items in the truck. Comparisons can help isolate an issue where it's interesting that rebel23 is not seeing an issue with about the same mass in the garage. Can you post a side pic of your rig on the TV ready for a trip? Some folks have had a sub-frame added to the trailer for a TV that sits too high. Nose of the trailer should be level or slightly down in the front.

Jim

[Hogdrv]

I do have everything you list except I only have 2 AC’s and it is just me and my wife so we are not loaded down, I have not been on the scales yet but I will one day. We do put everything but the bike on or in front of axles, I guess I’ve just been lucky so far. I am getting a little nervous now if or when we go on longer trips😳, like Oshkosh in July, and I fill the fresh water tank.

Jim