Upgraded Suspension Too Much?

[Rolltide2524]

Have a 2020 Transcend 265BH that had the Dexter 4400 with Sumo springs and Cree suspension.
After 5 trips across the US and one to Nova Scotia noticed inside tire wear on both axles . Bent Spindle and very worn springs.
Upgraded to the Dexter 5200 and springs with Road Armor and left the Sumo springs on.
For the record.
No I do not go over my trailer weight and yes it’s a little bouncy I assume from the stuffed animals on the floor after we arrived at our campsite on the first trip out.

So my question is should I back down to the 4400 springs on these axles or just let it ride and have the comfort of knowing i have more than enough strength and brakes for the crappy roads across our country?

Sorry for the poor grammar…

[Scott'n'Wendy]

I'd stay with the 5200's and the extra strength springs. I think that was a wise upgrade.

[Country Campers]

I have the Sumo springs on my RV. After spending a bit of time with Grand Design this week, especially the techs and repair folks, I will be removing the Sumo springs. What they have found is frame failure where the Sumo springs contact the frame. They have not seen many of these but the ones documented have been enough for me to make the change. Grand Desing does not recommend the usage of Sumo springs.

Just wanted to add this in for you.

Brian

[Rolltide2524]

Thanks for info. Not sure how they come to that conclusion on the Sumos . Seem far reaching for rubber to have any bearing on frame strength.. Not an engineer though.

[Rolltide2524]

Thanks Scott and Wendy. For feedback. Especially like the huge upgrade in brakes . We do a lot a passes out west and the more brakes the merrier.

[acoleman43]

Thanks for info. Not sure how they come to that conclusion on the Sumos . Seem far reaching for rubber to have any bearing on frame strength.. Not an engineer though.

Probably because the Sumo springs apply loads to the frame where the frame was not designed to absorb those loads

[Scott'n'Wendy]

What they have found is frame failure where the Sumo springs contact the frame.

Just wanted to add this in for you.

Brian

IMO...that is BS they are giving you. However...did they have any actual data or just a guess?

[Scott'n'Wendy]

Probably because the Sumo springs apply loads to the frame where the frame was not designed to absorb those loads

It's the same frame that has the hangers welded to it....so ....

[acoleman43]

It's the same frame that has the hangers welded to it....so ....

I know when I design trusses, the truss is designed for specific types of loads in specific places. If a load were to be off a few inches or feet, or the load changes category (live vs dead vs environmental, etc) the truss can fail. I don't know if it's the same concept with frames, but I'm thinking it probably is. Also, A load from the spring hangers is more of a progressive load that is shared by more nodes than a sumo spring (for single axle the spring uses 2 nodes per side where sumo spring uses 1, with a dual axle the springs use 3 nodes where the sumo springs use 2). This means the sumo spring load is greater than the load on the spring hanger. A sumo spring load more of an impact load than a progressive load - which has a different duration of load factor I'm guessing.

[Scott'n'Wendy]

Yes, I can see a truss being different though. A trailer frame is just a beam..no design change along it's length. I don't think the sumo would ever be a larger load than the springs. To start with the springs are holding up the entire axle share of the trailer weight. The sumo supports nothing. So at rest my 303 has somewhere in the area of 8500 pounds on the springs. Nothing on the sumos. Hit a bump and those springs exert more pressure on the frame and the sumos 'start' to exert a force on the frame. How much? I can't tell you but the springs are rated at something like 2600 pound? and the sumos are rated at something like 1800 pound.. don't remember for sure though.
My original point is that, imo, GD has no idea if they caused the failure. But it's an aftermarket part and manufacturers are famous for saying the aftermarket part caused the issue. Often without any data to back that up. If they have the data to show how they cause it I would be interested in reading it. I'll bet there are far more cracked frames without sumo springs out there

[Jlawles2]

Scott'n'Wendy Yes and no on the loadings. The springs in theory divide the load across 3 points. The center is taking about 1/2 the weight of the sides and the ends about 1/4 each. The Sumo on the other hand has a know rate of compression. At Y compression its x amount of support force.

So the big question then is what happens if you exceed the "capacity" of the Sumo??? Is the Sumo designed in such a way that it destroys itself at max load to prevent overloading of the system? If not, then the spring rate of the Sumo kicks in to high gear and increases force per deflection (springs are not truly linear but close) as polymers tend to have that property until you get cold flow (that's a completely different state).

GD stating that the Sumo caused failure is the typical answer as you suggest. Since they did not design the frame (per se) fully but had input on the design, the true rejection of claim would need to be evaluated ($$$$) by the design company. Thus it's just easier to say "You added something changing the load points, therefore Denied".

[Scott'n'Wendy]

I should qualify my mechanical suspension opinions are coming from a fully qualified electrician...lol
However, I'm going to email SuperSprings Intl and see what they have to say..if anything in rebuttal. I will post up the answer if I get one.

[Skilletface]

Have a 2020 Transcend 265BH that had the Dexter 4400 with Sumo springs and Cree suspension.
After 5 trips across the US and one to Nova Scotia noticed inside tire wear on both axles . Bent Spindle and very worn springs.
Upgraded to the Dexter 5200 and springs with Road Armor and left the Sumo springs on.
For the record.
No I do not go over my trailer weight and yes it’s a little bouncy I assume from the stuffed animals on the floor after we arrived at our campsite on the first trip out.

So my question is should I back down to the 4400 springs on these axles or just let it ride and have the comfort of knowing i have more than enough strength and brakes for the crappy roads across our country?

Sorry for the poor grammar…

IMHO, it appears that you are someone who actually uses their RV and your upgrades maybe well founded, as you only increased axle capacity by 800 lbs. As for the Sumo Springs, I think some think of them as jounce protection and do not have them installed correctly. I can see where if the Sumos are allowed to separate from the frame and then make frame contact under pressure it could have an effect on the frame. Also keep in mind there are compression ratings on the Sumo Spring lineup.
Should you decide to go back to the 4400 - 4500 lb. spring, check into a 6 stack leaf spring, again IMHO, PHD from the university of hard work, I see the widely used 4 stack as adequate for the lesser used RV but not for the actually using it market.

[Kathy&Jim_Imagine]

I don't currently use/have sumo's but after reading the comments wonder Is it that the sumo does'nt allow the TT springs to function correctly (allow for as much travel) which may put extra stress on the mounting points?? Just a thought.... Did GD say where they are seeing the actual failure on the frame?

[howson]

All -- realize that what is documented in this thread is NOT intended in any way, shape, or form to be passed along as an official statement representing GD. Your moderators are NOT GD employees.

I will, though, agree that the moderators did hear from multiple individuals (with first-hand knowledge) that they've seen catastrophic wall damage in TTs equipped with Sumos. I'm in no way qualified to speak to suspension systems, so take that into consideration when I write that what I heard is that a Sumo reduces the overall travel of the suspension as intended/designed. The impact is transferred through the frame to the wall system when the suspension bottoms out.

As with any subject, your moderators pass along what we learn and then it is up to each individual whether to accept or reject the input. Frankly, I'm not sure what one would expect from an aftermarket company if queried about their product. Do we expect anything other than it's the best thing since sliced bread?

Howard