2021 Zion SRT Rear Ride Quality Improvement Options.

[abhijitz]

Hello,

I am new to this forum and recently acquired a 2021 Zion SRT. We went for a 4-day camping trip and each way was an 8-9 hour drive. It seems the passengers at the rear seat (my wife and 6 yr old son) are not comfortable and complained of extreme bumpiness during the trip.

What are my options for improving the ear ride quality? I first though of re-doing the rear sofa bed upholstery to a firmer & thicker setup (or some sort of re-inforcement). Then i read on few posts of Class B owners improving their RV's rear ride quality with suspension upgrades.

I inquired with a local vendor and he recommended i switch to Konis front + rear and install a Hellwig swaybar. The cost is not minimal, specially the labor.

Is this complete upgrade required? I was thinking of starting with the rear shocks first (which i can replace myself). If that is going to help the ride comfort, which brand/model would you recommend.

Appreciate your input.

PS : Located in Bay Area, CA

[rowiebowie]

Welcome to the forum!

Sumo Springs first, then new rear shocks if not satisfied. Sumo Springs are really not springs, but rather bump stops that support and reduce ride movements. The are almost universally praised regardless of which van chassis they are used on. Not expensive and a DIY job since you've said you can handle shocks.

Good luck.

[mumkin]

Originally Posted by rowiebowie

Sumo Springs first, then new rear shocks if not satisfied. Sumo Springs are really not springs, but rather bump stops that support and reduce ride movements. The are almost universally praised regardless of which van chassis they are used on. Not expensive and a DIY job since you've said you can handle shocks.

He already has sumos in the rear as they are now an option for the new Roadtreks. Besides, sumos don't make the ride smoother in the rear... probably make it worse. They improve the handling in wind... and the roll on cornering. But, our poster's wife is unhappy with the bounce in the rear.

I'd try the shocks first... and then try the sway bar.

[booster]

I think I see the function of the various items a bit differently than some others.


Sumos are springs as they pickup weight and continue allowing suspension travel as they stiffen up with more compression. If they are hitting the axle all the time they are full time springs, if they hit it only after some travel they are overload springs, IMO. Bump stops merely do that function, give a softer, less noisy, end of travel.


What will address the problem of this discussion has to be based on what the complaint is. Is it about being just too stiff so the suspension and short quick travel with a lot of that reaching the body of the van? Is it because it moves some amount and then hits on something that slows it quickly so get a jolt? Is it long lazy oscillation like in a boat on waves? Perception between individuals is very different and the different issues will affect some and not others.


I agree with Mumkin that Sumos can make the rear ride worse, because the stiffen up the suspension on the rear axle by adding springrate. They are better for handling and wind issues, although that can also be done with other methods. If too stiff is the issues, the Sumos are contributing to it.


Shock changes might or might not make it better or worse, depending on what shocks are in it and what shocks you get. Just getting higher damping shocks probably will make it worse unless the issue is long lazy waves of travel. Going to variable rate shocks will make the small to mid size bumps less harsh but big bumps likely firmer.


Adding a swaybar will have very little effect on ride quality a lot of the time as it doesn't do anything at all if both rear wheels are moving up and down together like on dips in the road or a rough expansion strip repair across the whole lane. On single wheel bumps it will make that bump somewhat harsher, but also prevent to rapid tilt of the van you get from and one wheel bump or dip in the rear.


The shop's recommendation of the shocks and swaybar is not all bad, but might not be complete and the parts would need to be carefully selected. If the stock shocks are very stiff, which is not very likely I think, going to a variable rate shock might help harsh ride some. The swaybar will not do much for making ride better at all unless the issue is side to side sway.


There is a possible solution that might work well if the issue is harshness and rider with issues is not the type to that doesn't like the longer lazier travel motions. It is what we finally settled on in our Roadtrek 19 on a Chevy chassis. We had airbags for year, to lift the van and they also made it smoother because of their lower spring rate, but on big bumps the suspension hit the big overload leaf in the springs that would be somewhat similar to how a Sumo functions. We would get decent smooth travel and thump hard onto the overload with a jolt. I finally changed our airbags to ones with internal bump stops just in case the airbag popped and then removed the overload leafs from the springs. This allowed the axle to move further on the lower springrate bags and the rest of the spring pack. Longer, smoother, quieter, less harsh rear travel were the results and suits us well. If the rider with issues is OK with longer and smoother motions, something similar might be in order for the OP. With ours, I then replaced the rear swaybar with a larger one to pick up the increased little bit of sway we would get because of softer springs.


I can't say how it would all work on a Promaster as I have never had a chance to drive one much or try to make one better, but perhaps going to a lower stiffness Sumos, high end variable rate shocks, and a swaybar might be very similar. This is kind of what the shop recommended, but adds in the springrate reduction.


As far as DIY goes, it all depends on your skill level and tool collection. Shocks usually aren't too bad, swaybars a notch above the shocks in difficulty and changing Sumos not too bad, IMO.


All of this stuff is so interactive with each part changed on the others, it gets kind of complex, and if you throw in all the personal perceptions in regards to ride and handling quality, it gets even more complicated. There is no one size fits all solution for this kind of thing,IMO.

[jrobe]

Originally Posted by abhijitz

It seems the passengers at the rear seat (my wife and 6 yr old son) are not comfortable and complained of extreme bumpiness during the trip.

Rear seat bumpiness was the biggest problem in our Sprinter too when it was new. After considerable research, we decided to try the following in this order.

First we upgraded the tires to high quality Michelin tires and made sure that they tire pressure was perfect for the exact weight of our van. This helped a lot.

Then we upgraded the rear shocks to custom tuned Fox shocks that I bought from Agile Off Road ($300 or so as I recall). I gave them our van weights and they tuned the shocks for these weights. They were easy to install myself.

I also installed Sumo Springs but I doubt these helped much with rear seat bumpiness.

The next step would have been rear leaf springs assists but we were so happy with our results from the tires and shocks that we no longer felt the need to spend more money.

In my own simple mind, I looked at the problem and solutions something like this.

1-Rough ride from small bumps (highway expansion joints, etc.) - correct with good tires and proper tire pressure (often lower pressures).
2-Rough ride from large bumps - correct with spring assists and better shocks
3-Rocking after going over bumps (oscillations) - correct with better shocks
4-Poor handling in corners (roll and sway) - correct with sway bars

[Rlum]

Originally Posted by abhijitz

Hello,

I am new to this forum and recently acquired a 2021 Zion SRT. We went for a 4-day camping trip and each way was an 8-9 hour drive. It seems the passengers at the rear seat (my wife and 6 yr old son) are not comfortable and complained of extreme bumpiness during the trip.

What are my options for improving the ear ride quality? I first though of re-doing the rear sofa bed upholstery to a firmer & thicker setup (or some sort of re-inforcement). Then i read on few posts of Class B owners improving their RV's rear ride quality with suspension upgrades.

I inquired with a local vendor and he recommended i switch to Konis front + rear and install a Hellwig swaybar. The cost is not minimal, specially the labor.

Is this complete upgrade required? I was thinking of starting with the rear shocks first (which i can replace myself). If that is going to help the ride comfort, which brand/model would you recommend.

Appreciate your input.

PS : Located in Bay Area, CA

Hi: I have a 2016 PW on Promaster 3500 chassis. First installed yellow sumo springs(originally came with black ones) with front sumo coils. Helped with long slow floating feeling. Recently upgraded to Michelin tires. This helped a lot with handling, tracks much better. Replaced rear shocks with Bilsteins( leaking rear shock) and finally added an extra leaf spring from Super Springs(same company as sumo springs). Finally I am happy with handling of the van. It drives and handles much better. Added the Super Springs because wanted a bit more height in rear for new genny.

For your issue: I would recommend you add air bags. This way you can adjust the air bag pressure to ride comfort to match your wife's desire.

[booster]

Originally Posted by Rlum

Hi: I have a 2016 PW on Promaster 3500 chassis. First installed yellow sumo springs(originally came with black ones) with front sumo coils. Helped with long slow floating feeling. Recently upgraded to Michelin tires. This helped a lot with handling, tracks much better. Replaced rear shocks with Bilsteins( leaking rear shock) and finally added an extra leaf spring from Super Springs(same company as sumo springs). Finally I am happy with handling of the van. It drives and handles much better. Added the Super Springs because wanted a bit more height in rear for new genny.

For your issue: I would recommend you add air bags. This way you can adjust the air bag pressure to ride comfort to match your wife's desire.

I would absolutely agree on the air bags. I didn't even know they were available because I have never seen them mentioned. Airlift is what we have, and they are very good from what ours have shown.



For Promaster you can get with out without the internal bump stop, but I would get the one with the stop and take out the Sumos and see if she likes it that way at some pressure more than others.

[RvLee]

Originally Posted by abhijitz

Hello,

I am new to this forum and recently acquired a 2021 Zion SRT. We went for a 4-day camping trip and each way was an 8-9 hour drive. It seems the passengers at the rear seat (my wife and 6 yr old son) are not comfortable and complained of extreme bumpiness during the trip.

What are my options for improving the ear ride quality? I first though of re-doing the rear sofa bed upholstery to a firmer & thicker setup (or some sort of re-inforcement). Then i read on few posts of Class B owners improving their RV's rear ride quality with suspension upgrades.

I inquired with a local vendor and he recommended i switch to Konis front + rear and install a Hellwig swaybar. The cost is not minimal, specially the labor.

Is this complete upgrade required? I was thinking of starting with the rear shocks first (which i can replace myself). If that is going to help the ride comfort, which brand/model would you recommend.

Appreciate your input.

PS : Located in Bay Area, CA

Hello, I have 2018 Roadtrek Simplicity SRT. I've had both Sumo and Air bags. Both did not improve the harsh ride. After researching and reading forums, I have set my tire pressure to 60psi on all four tires.Some members even set to down to 55psi. Just set the TPMS to 55 to 60.

[rowiebowie]

Originally Posted by RvLee

Hello, I have 2018 Roadtrek Simplicity SRT. I've had both Sumo and Air bags. Both did not improve the harsh ride. After researching and reading forums, I have set my tire pressure to 60psi on all four tires.Some members even set to down to 55psi. Just set the TPMS to 55 to 60.

Welcome to the forum Lee!

These vans are heavy and most require load range E tires and higher psi in order to safely handle the van's weight. I don't know the Promaster chassis, but on other chassis the psi recommedations you state would be below minimum manufacturer's load ratings for rear axles and therefore unsafe.

[GeorgeRa]

I have 2013 Sprinter 144”WB DIY conversion based on the passenger model. Seating in the rear is perfect as it was with passenger van before my conversion. Rear suspension is different between passenger and cargo models. I would suggest to research if passenger suspension can be adapted to your van weight permitted.

This fellow changed his rear suspension to passenger style. https://sprinter-source.com/forums/i...5/#post-527344

[MsNomer]

Have you checked promasterforum.com? Some people with the 159” PM remove one of the leaf springs to achieve a ride more like the 136”. I suspect your build is heavy, though. I second the concerns about the tires.

[abhijitz]

Sorry, i was out on a 5-day camping trip with the van and had no access to the internet. Lots of great suggestions and i will respond in this post soon.

[mkguitar]

I've posted on the sumo springs on my Chev. front and rear



happy with them


they come in various densities, I chose Black after some said the Yellow were too stiff


these were mostly to dampen side to side rocking in wind or on curves- the motion is reduced and spread over time


your family may be suffering "back of the school bus syndrome" though



Mike

[booster]

Originally Posted by MsNomer

Have you checked promasterforum.com? Some people with the 159” PM remove one of the leaf springs to achieve a ride more like the 136”. I suspect your build is heavy, though. I second the concerns about the tires.

Think this brings up an "outside the box" way of looking at the suspension comfort vs control stuff.


Harsh, jittery, ride is a common trait of leaf spring suspensions, so if you want to do anything about the comfort you may need to look at other technologies, or hybrids IMO.



We had harshness and also bottoming on the overload leaf in our Chevy Roadtrek and finally decided to go to a different solution than is normally considered.


All you need to do is look at OTR trucks or trains claims to get the idea that "air ride" AKA air bags, give a smoother ride.The why is that they are not as progressive in spring rate, mostly. So what would happen if you took half the load off your leaf springs and removed a leaf so the spring rate matched the load. Softer ride. Then you put the removed 1/2 of load onto a lower spring rate air bag. Probably lower spring rate or close to if you are lucky. Bottom line is smoother ride, which is the important part, but still with adequate load carrying capacity.


We have done this experiment in our 07 Chevy Roadtrek 190 by removing the high rate overload spring leafs. Those leafs picked up the load on most bumps, even minor dips. We then put 40% of the load onto air bags which are much lower spring rate than the massive oveloads are. Ride got smoother and less jittery, with longer, lazy travel rather than rapid jittering. Ride got a whole lot better. Sway got a bit worse, though because of less springrate, so the swaybar in the rear was upsized 1/8" in diameter bring it back to where it was. Then all was very good.



There is no one size fits all suspension upgrades that apply to all cases and users. The best solutions are developed to fit the application.


Our van is much more comfortable to be in now, and is much smoother and quieter. Don't be afraid to try some not in the mainstream stuff you think might work well. You never now, as long as you survive the testing it might be a great solution.

[abhijitz]

Thanks for all the comments. Summarizing here ... [ Sorry again for being MIA, my work is mobile and i get to use no public internet when i am sent to a site ]

1. Sumo Springs : Already have them at the rear from the factory, the yellow ones.
2. Sway Bar : Did not feel it was necessary as all it would be improve is lateral movement from winds sharp turns and that is not what the passengers are complaining about.
3. Replacing leaf spring : Well, That will be too much of a DIY for me, and the labor rate at Bay Area has sky-rocketed. Plus it is an RV/motorhome and only few people work on it.

======

Follow-up question for the members :


@booster : Can i add air bag along with the yellow Sumo Springs? Wouldnt i need to go to Softer Sumo Springs, if i am adding air bag into the mix.

@jrobe : The solution you described, is what i am gearing towards. I have been referred to the Michellin Agelis tires (Is that the Michellin Model you meant?). Fox shocks are currently unavailable. I have been trying to find them. Any leads? The GVWR of the vehicle is 10,000 lb.

Again, sorry for the delay again ... but i really appreciate all of your help and really want to find a solution. otherwise, the "house leader" is complaining to the extent i may have to just sell the vehicle.

[booster]

Originally Posted by abhijitz

Thanks for all the comments. Summarizing here ... [ Sorry again for being MIA, my work is mobile and i get to use no public internet when i am sent to a site ]

1. Sumo Springs : Already have them at the rear from the factory, the yellow ones.
2. Sway Bar : Did not feel it was necessary as all it would be improve is lateral movement from winds sharp turns and that is not what the passengers are complaining about.
3. Replacing leaf spring : Well, That will be too much of a DIY for me, and the labor rate at Bay Area has sky-rocketed. Plus it is an RV/motorhome and only few people work on it.

======

Follow-up question for the members :


@booster : Can i add air bag along with the yellow Sumo Springs? Wouldnt i need to go to Softer Sumo Springs, if i am adding air bag into the mix.

@jrobe : The solution you described, is what i am gearing towards. I have been referred to the Michellin Agelis tires (Is that the Michellin Model you meant?). Fox shocks are currently unavailable. I have been trying to find them. Any leads? The GVWR of the vehicle is 10,000 lb.

Again, sorry for the delay again ... but i really appreciate all of your help and really want to find a solution. otherwise, the "house leader" is complaining to the extent i may have to just sell the vehicle.

The Sumos and airbags often are put int he same spot, so can't have both with doing it some other way.



When we did ours, we used the airbags that have a small bump stop inside them to prevent bottoming and give a soft landing on bit bumps. It is like minim Sumo inside the bag itself. It also allows the bag to have no pressure without the van dropping to far, which a good reassurance in case something happens to the bag or hoses.