Undersized axles on Momentum 320G or just poor design?

[RoyB]

Does something seem askew here?

I have a 320G. Literature numbers below.

UVW: 12,400 lbs
Hitch: 2,300 lbs
GVWR: 16,800 lbs


My sticker:
UVW 13,180lbs which is 780 lbs heavier. That makes sense since I have generator (300 lbs) 3rd AC (100 lbs), Awnings (200), Stereo (50) 3 Season door (100), HD ramp (50)

In theory, I should have ~10,580 lbs on my trailer axles and ~2600 lbs on hitch. Generator is sitting up front and all the other options are in the rear. I went and weighed and these are my numbers

Unloaded, ready for camping (no toys, no water)

• Hitch: 2,620 lbs (17.75%)
• Axles: 12,120 lbs
• Total: 14,760 lbs.

By these numbers, I was pretty accurate on the hitch. However, the axle weight has me confused. Total weight over sticker= 1580 lbs. This, to me, seems like a lot. We don't have that much stuff in the camper aside from the usual tools/wood/chocks/linens/plasticware/. I think I had the 30 gallon fuel cell full (240 lbs).


The numbers look OK, but this is where things get wonky. I weighed again with my 900lb cycle and 80 gallons of water ~1500 lbs. Here's what it did to the numbers


Loaded, ready for camping (900lb bike, 80 gallons water= approx 1500 lbs)

• Hitch: 2,140 lbs (13.16%)
• Axles: 14,120 lbs
• Total: 16,260 lbs.

Axles are rated 7K lbs so those are overloaded. Under GVWR by 540 lbs, over on axles and pin is too light imo. The result was adding 1500 lbs removed almost 500 lbs from the pin and put it all (2000 lbs) squarely on the trailer axles. I rearranged stuff, grill/spare tire to the front. Took some stuff out, removed the OEM tables, etc. Below are my new numbers

Loaded, ready for camping (900lb bike, 80 gallons water= approx 1500 lbs)

• Hitch: 2,400 lbs (14.80%)
• Axles: 13,800 lbs
• Total: 16,200 lbs.

I am a little confused how I can be so far under GVW but axles are maxed out. From what I can tell, the balance is way off on this thing. IF the hitch was closer to 20% like a 5th wheel should be (3200 lbs) that would lighten up the trailer axles allowing me to max out GVW and be under/right at axle limit. Axles would have roughly 13,000 lbs or less as it sits. I could add in the 600 lbs the garage and be right under 14,000 lbs on the axles and not have to drain all the water.

Instead I am pulling everything we don't need out of the camper or putting it under the front bunk to shift as much weight to the hitch as possible. There's nothing left to move. Is this a huge design error on GD part? Did someone mix my fresh water and grey water tanks up? I have (2) 700lb ATVs and I'm not sure I'll be able to travel with them and any water at this point, unless I upgrade the axles to 8000 lb units. And at that point, I am afraid that the hitch will be extremely too light. I estimate those 2 ATVs and 3/4 tank of fresh water to put approximately 700 lbs on the trailer axles and remove 200 from the hitch.

Estimated Loaded, ready for camping (2 x 700lb ATVs, 80 gallons water)

• Hitch: 2,200 lbs (13.17%)
• Axles: 14,500 lbs
• Total: 16,700 lbs.

What's everyone's thoughts on this? Is this toy hauler not designed to haul toys? Should I upgrade the axles and pray it tows ok? Sell it for a better balanced trailer?

[howson]

What's everyone's thoughts on this?

First thought: you have an exceptional grasp on the topic for a new owner. (Which is good!) Is your 320G new? The VIN in your profile is "320G" (the model) so can't tell what year it is.

Second, since that was your first post check out the Welcome Letter to New Members https://gdrvowners.com/forum/main-fo...to-new-members

Third, I'm at work so I don't have access to my files. Hopefully one of my fellow moderators can check or I'll (try to remember) to look it up when I get home later tonight regarding the location of the black and gray tanks in your trailer.

Why? Well....this is not ideal, but just a thought. Depending on the tank configuration, perhaps carrying less fresh water in trailer is an option while adding water to the gray (or black) tank closest to the pin. The purpose, obviously, is to shift weight to the pin and remove it from the axles.

Howard

Country Campers
Cate&Rob
@TucsonJim

[RoyB]

First thought: you have an exceptional grasp on the topic for a new owner. (Which is good!) Is your 320G new? The VIN in your profile is "320G" (the model) so can't tell what year it is.

Second, since that was your first post check out the Welcome Letter to New Members https://gdrvowners.com/forum/main-fo...to-new-members

Third, I'm at work so I don't have access to my files. Hopefully one of my fellow moderators can check or I'll (try to remember) to look it up when I get home later tonight regarding the location of the black and gray tanks in your trailer.

Why? Well....this is not ideal, but just a thought. Depending on the tank configuration, perhaps carrying less fresh water in trailer is an option while adding water to the gray (or black) tank closest to the pin. The purpose, obviously, is to shift weight to the pin and remove it from the axles.

Howard

Country Campers
Cate&Rob
@TucsonJim

Thank you. This is a 2020 Momentum 320G. We built and purchased new last October. It's our first 5th wheel, but not our first camper. We settled on the 320G because it was one of the only dedicated garage campers under 38' (my limitation for where I store it).

On paper, CCC looked good. Hitch looked light but I was expecting a company like Grand Design to know what they were doing. We usually travel with water because we don't always know if there will be water at the CG. For instance this last trip a couple weeks ago, the water was turned off since it was below freezing the week before. They also did not have water at the site so we would had been waterless the weekend. We also have city water (vs well) which keeps much better since it doesn't get stagnant. As a result, I rather not fill our tanks with well water if at all possible, which I imagine is at most CGs. I fill it up 100%, but by the time we get to our destination, about 25% of it siphons out.

From what I can tell, the Fresh water is just behind the rear axle. I am guessing rear black tank is right over the axles, followed by grey just in front of axles and front black tank I imagine is most forward. Purely speculation, but it seems the most logical on how everything is arranged. I will say that when I was overloaded on the axles and 13% pin, the trailer towed straight as an arrow.

We have approximately 3000 miles towing on it so far. We love the camper other than this weight and axle issue

[TucsonJim]

Welcome to the forum. Kudos to you for weighing your rig and your knowledge of the specifications and requirements.

Unfortunately, the drawing package I have for the 320G is very sparse. I have a tank layout drawing, but they did not label the tanks. And this drawing package did not include a DWV drawing. So take my answer with 80% accuracy.

It appears you have a large gray tank up front on the driver's side. This will capture the front bath and kitchen gray water. You have a black tank for the front bath on the passenger side. Both of these tanks run parallel to the frame and are centered under the master bedroom.

Farther aft, you have a combined black/gray tank for the rear bath. It is located right under the rear bath toilet, and runs perpendicular to the frame.

Going farther aft, it appears your fresh water tank is located under the garage, right under the front wall.

Finally, you have a fuel tank a few feet from the back wall.

Filling the fresh tank will just put more weight on the back and further unload the king pin.

Jim

[RoyB]

Welcome to the forum. Kudos to you for weighing your rig and your knowledge of the specifications and requirements.

Unfortunately, the drawing package I have for the 320G is very sparse. I have a tank layout drawing, but they did not label the tanks. And this drawing package did not include a DWV drawing. So take my answer with 80% accuracy.

It appears you have a large gray tank up front on the driver's side. This will capture the front bath and kitchen gray water. You have a black tank for the front bath on the passenger side. Both of these tanks run parallel to the frame and are centered under the master bedroom.

Farther aft, you have a combined black/gray tank for the rear bath. It is located right under the rear bath toilet, and runs perpendicular to the frame.

Going farther aft, it appears your fresh water tank is located under the garage, right under the front wall.

Finally, you have a fuel tank a few feet from the back wall.

Filling the fresh tank will just put more weight on the back and further unload the king pin.

Jim

I would say that sounds 100% accurate. The grey water takes longer to come out of the drain than the black, so it being further away on the passenger side makes sense now. Why would GD design the fresh water behind the rear axle? I guess one could argue that is a more optional tank to keep filled vs the Black/Grey.... But I would think flipping the rear Grey/black with the fresh water would had been the ideal setup since the rear toilet doesn't generally get the use the front grey/black get. Plus that large a tank centered over the axles would have less of a rocking motion vs closer to the end of the camper.

My previous TT had the fresh water the most forward. I kept it filled to keep the hitch weight down since it towed better.

[howson]

RoyB -- for the siphon problem, check out a recent thread by TucsonJim on the topic. https://gdrvowners.com/forum/operati...flow-revisited

[Country Campers]

It is curious that the tank layout is this way. I think a tag GDRV-Megan. Please see the above posts and relay to the Momentum crew. Having the fresh water tank behind the axels removes some of the "toy box weight" as well as decreases pin weight when the "toy box" has a toy in it. Moving the fresh tank forward to under the kitchen area may be a better position , but while typing that it is possible that the kitchen slide mechanisms may interfere with that position.

Brian

PS. RoyB We spent a week under the lighthouse at that Summersville campground a few years ago , beautiful country in those parts.

[RoyB]

RoyB -- for the siphon problem, check out a recent thread by TucsonJim on the topic. https://gdrvowners.com/forum/operati...flow-revisited

I will check it out. I've read a few people that put valves and higher vent hoses on. We seem to be getting by with the 3/4 tank so far so I haven't put much effort into a fix yet

It is curious that the tank layout is this way. I think a tag GDRV-Megan. Please see the above posts and relay to the Momentum crew. Having the fresh water tank behind the axels removes some of the "toy box weight" as well as decreases pin weight when the "toy box" has a toy in it. Moving the fresh tank forward to under the kitchen area may be a better position , but while typing that it is possible that the kitchen slide mechanisms may interfere with that position.

Brian

PS. RoyB We spent a week under the lighthouse at that Summersville campground a few years ago , beautiful country in those parts.

Thank you. Our break-in maiden voyage was a 2 week 2500 mile round trip adventure. Leaving Chicago, through Kentucky, West Virginia, North Carolina, Tennessee, and home. Every place we stayed was absolutely stunning. We were able to get the cycle out and ride the Smokies a little. We were hoping to make another trip like that this year, but with Covid, we stayed local.







Not being able to haul the quads, some fresh water and fuel is going to be problem-some though. I am hoping I can at least get the quads side by side as far forward as possible. If that's not possible I will have to turn each sideways putting more weight at the back end of the garage making the problem worse. I shouldn't have to worry about how I am going to load an 11' garage on a toy hauler so that it's not overloading the axles. It doesn't take much seeing how just my cycle and water were overloading the axles before I moved as much as I could to the front.

[TucsonJim]

But I would think flipping the rear Grey/black with the fresh water would had been the ideal setup since the rear toilet doesn't generally get the use the front grey/black get..

I'm not sure they could do that. The rear toiled waste goes nearly straight down to the holding tank. If you switched them, then you'd have a run of several feet to get the toilet waste over to the dual purpose tank. That could be real problematic.

Jim

[ThePowells]

RoyB Thank you for the pic with the deck over that crystal clean creek. You just muddied the argument over the next (and better be last) addition to our family......

[RoyB]

RoyB Thank you for the pic with the deck over that crystal clean creek. You just muddied the argument over the next (and better be last) addition to our family......

We were able to overhang at 2 of the campgrounds that both had streams. Sitting on the deck watching the stream while drinking coffee in the mornings and wine at night was the bees knees. When the temperatures dropped we just sat on the hapijacks and peered through the 3 season wall which was almost as inviting.

[SBARLAG]

This is a very minor point in the big picture, but the literature UVW is just an average and not the actual weight of your unit. The data label on the ODS is the actual weight of your unit.

[Canyonlight]

RoyB Thank you for the pic with the deck over that crystal clean creek. You just muddied the argument over the next (and better be last) addition to our family......

X2 RoyB - no help here on your topics but your pictures of fall camping in awesome locations are pretty darn nice ! These remind us of one of the key reasons we enjoy this lifestyle !

Dan

[RoyB]

In looking at GD website, they clearly indicate an 1800 lb side by side (Canam Maverick?) will work with a 320G. Curious how overloaded the axles are with something that heavy in there.

X2 RoyB - no help here on your topics but your pictures of fall camping in awesome locations are pretty darn nice ! These remind us of one of the key reasons we enjoy this lifestyle !

Dan

Fall camping is the best. Thank you for the kind words.

[GDRV-Megan]

It is curious that the tank layout is this way. I think a tag GDRV-Megan. Please see the above posts and relay to the Momentum crew. Having the fresh water tank behind the axels removes some of the "toy box weight" as well as decreases pin weight when the "toy box" has a toy in it. Moving the fresh tank forward to under the kitchen area may be a better position , but while typing that it is possible that the kitchen slide mechanisms may interfere with that position.

Brian

PS. RoyB We spent a week under the lighthouse at that Summersville campground a few years ago , beautiful country in those parts.

Thanks for the tag and the feedback. I have passed this along to our product manager. I'll update here if I get any feedback. Thanks!

RoyB beautiful photos!! I'd love to share these on our social media platforms, with your permission! If you'd like us to share, please send them to me at smservice@granddesignrv.com attn: Megan. If you'd like credit or a shout out, please include your first name or Instagram account handle.