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2014, 138WB, High Roof, Gas, SW MT
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Discussion Starter #1
Hi,
Have had our 136 WB, `high roof 1500 camper conversion since 2014 and now have 43K miles on it.

We use it on some backroads (500+ miles on our Yukon trip), and generally its fine -- ground clearance and traction are fine for us. The ride can be a bit rough over rocks and such, but to be expected on backroads -- just go slow and its fine.

The one thing that is really bothersome is its ride on wash boarded roads -- its just really really rough. Feels like the van is about to come apart. Can slow down to 3 or 4 mph and that helps a lot, but if you have 10 or 20 miles to go, its kind of slow.

Have driven many vehicles on back roads since the 60's, and have never had a vehicle that was quite so jarring on wash boards.
It feels like a resonance phenomenon and seems to be at its worst and 15 to 20 mph you would like to travel over the wash boards.

Any ideas on what might be effective to get a better ride on wash boarded roads?

Shocks, springs, other suspension changes?

I'm fine with making some changes, but don't want to just randomly try things.

I have tried reducing tire pressure and this does help some.

Thanks --Gary
 

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When I did my Baja trip last year I encountered plenty of washboard. Soulution I used, air down the tires. I’d drop all the way to 30psi and most of the washboard jarring disappeared. Of course, you need to have some equipment (and time) - auto tire deflators (unless you like to spend a lot of time on your knees playing with the valve stems) and a good 12v air compressor. AND, you shouldn’t plan on going anywhere in a hurry, I normally cruised the washboards at 45mph or so.
 

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Have you tried going faster? Where I grew up the roads were notorious for long sections of washboard. I was almost always driving heavy duty pickups back then so the only two options were to slow down to almost nothing, or speed up fast enough to skip over them.
 

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We found the ride improved immensely when backing down the road. So this leads me to think the spring rate is the key. Set up too harsh and too unsophisticated to be comparable to any modern pickup. Makes me wonder how they ride when loaded up to 50% of payload capacity.


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The rear springs are the only thing about the Promaster that is unsatisfactory IMHO other then van the uC 5 of course ;)
 

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2014, 138WB, High Roof, Gas, SW MT
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Discussion Starter #7
Thanks for the suggestions.

Guess I will get a better quality 12 volt compressor and try airing down more.
Maybe to the secondary leaf removal.

Any thoughts on whether new/different/softer(?) shocks might help on the rear?

edit: I wonder about having custom springs made for the rear? Or, is it the layout of the rear suspension that is the problem?

Gary
 

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.....cut.....
It feels like a resonance phenomenon and seems to be at its worst and 15 to 20 mph you would like to travel over the wash boards.

Any ideas on what might be effective to get a better ride on wash boarded roads?

Shocks, springs, other suspension changes?

I'm fine with making some changes, but don't want to just randomly try things.

.....cut.....
You're correct that the problem is caused by resonance. When the forcing frequency from the road (based on washboard pitch and vehicle speed) matches the suspension's natural frequency (depends on mass and spring), the vehicle will bounce around at even greater amplitude than the road surface irregularity.

I think it's wise on your part to avoid random modifications without knowing how they will affect the results. If your interested in the basic math let me know and I'll try to post a graph that shows how these things relate.
 

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2017 2500 HiTop 159 Cargo Van white.
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Drive faster. Just go. When you get to the right speed it just smooths out and floats.
 

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2014, 138WB, High Roof, Gas, SW MT
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Discussion Starter #11
You're correct that the problem is caused by resonance. When the forcing frequency from the road (based on washboard pitch and vehicle speed) matches the suspension's natural frequency (depends on mass and spring), the vehicle will bounce around at even greater amplitude than the road surface irregularity.

I think it's wise on your part to avoid random modifications without knowing how they will affect the results. If your interested in the basic math let me know and I'll try to post a graph that shows how these things relate.
Hi Chance,

Yes -- would like to see the graph.

Gary
 

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Logged a lot of dirt road miles this summer in eastern Montana and agree with the idea of going faster rather than slower on washboard. (The same applies on a mt bike).
 

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Did quite a few miles on rough oil field roads as a mud engineer at high speeds, course the vehicle wasn't mine, and experience in oval dirt track racing. Just let'er rip and raise a little up off your seat and flex your knees as you would on a dirt bike. :D Jus' kiddin'. ;)

Actually, I don't know if I'd do that in a tall van with a stiff suspension with a relatively light load especially if I owned it. Seems a little scary and could see how you could easily lose control especially on a gentle or not so gentle curve unless you're an experienced dirt track racer and can control a power slide. In one race we would tear up the right front tire and there was always welds coming loose. I think your van at high speeds on washboard terrain would vibrate some stuff loose and wear your tires and your suspension out prematurely. Am too old to go fast anymore, so maybe less tire pressure and go slow or just find a better smoother path.:)
 

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Actually the hi top 159 is steady as a rock at all times. The real problem (for us self converters) is the fact that FCA seems to believe no one would want a 159 hi with a softer suspension. They believe that these vans will be mainly used as a truck to haul. Silly boys, I know, but when has corporate ever listened to their base? You can specially order a "touring" suspension in the window versions and perhaps with any special order but try and find one on a dealers lot!
 

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Hi Chance,

Yes -- would like to see the graph.

Gary
Gary, for a vehicle it's a lot more complicated than a simple chart, but this helps understand what takes place. At very low speeds the vehicle will move up and down the same amount as the amplitude of the bumps. As you increase speed and the forcing frequency of the bumps match the suspensions natural frequency, the vehicle's up and down movement is actually magnified. If driving in this range you'd want lots of damping to minimize amplitude.

As you go faster still so that forcing frequency is well above suspension natural frequency, the vehicle will move up and down much less than amplitude of bumps on road. In this range you benefit from having less damping, not more. Basically, when you go fast there isn't enough time for the vehicle to go up and down to keep up with washboard frequency.

One issue that's not taken into consideration in a simple graph like this is that the suspension has unsprung mass, so you can only go so fast before the tires can travel up and down fast enough to keep up with washboard frequency. At that point tires will skip from one bump to the next.

One area where ProMaster is much different than a regular truck is that rear axle is much lighter, so it will be able to follow road contour to a higher speed. That may explain why your PM feels different than previous trucks.
 

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P.S. -- By the way, if your worst speed is between 15 and 20 MPH, then at just below 30 MPH the ride should start to feel no worse than going slowly. Note curves all pass by 1.0 magnification when forcing frequency is at 1.41 that of natural frequency. Beyond that speed it should start to smooth out more. Another variable that makes this more complicated is that front and rear suspensions often have different natural frequencies, and different levels of unsprung mass. Also it makes a difference when front and rear tires hit bumps at same time versus one axle at a time.
 

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2014, 138WB, High Roof, Gas, SW MT
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Discussion Starter #17
Hi,
We were in Big Bend NP last couple days and got a chance to try the go faster method a bit. Things do seem to settle down some at 30 mph. But, problem is that 30 mph is pretty fast for a lot of back roads (at least where we go) -- things like sharp rocks strewn over the road, turns, dips for dry streams all make going faster a bit more of an adventure than I like -- the chances of ending up in the ditch or with a blown tire seem too high to me. I guess going faster could work well on flat straight sections where the washboarding is the only issue.

Chance: thanks for the info -- took a quick look, but will look through it carefully when we get back home.

Gary
 

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2018 159 High Roof gas, BC, Canada
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How tough are our PMs when it comes to washboard roads and going faster?

I traveled some washboard a bit in my minivan (Dodge Caravan, 2011) and I didn't want to damage it so I avoided gravel roads. I remember thinking at the time: "I wish I had a jeep". Can our PMs handle it? Are they body-on-frame vehicles like trucks?
 

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No they are the more rugged unit body so such vibrations are transferred to the body directly. Don’t take that to mean it cant take the washboard, it can.
I spend lots of time on desert roads that require 4wd and high clearance and have hundreds of miles of unavoidable washboard. I have had three vehicles over the past 18 years used for at least 3,000 to 4,000 miles of it a year including some rock crawling across the roads of lava fields and washes in the Pinacate of Mexico (look it up). I have not seen any damage to suspensions except for two broken sway bar links on my current 4 runner. They had been badly corroded by my daughters owning it in the salt of NH for 10 years and the replacements have been fine. I have pushed through running washes up to the top of the tires, jacked myself off a high center once with my F150 with the camper on it, traveled some roads the jeeps we saw could not believe we could go and that they were reluctant to try (scratches you know). I am not timid but I don’t rush these things except for finding the magic speed on washboard. Steve (of "The Backroader” fame) stopped on his return from the Baja in his 159”. He described his van’s limit in some challenging situations. The van is limited by it’s being 2wd and a bit by it’s clearance but not by it’s ruggedness. Go forth and wander- dirt!
 

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One issue that's not taken into consideration in a simple graph like this is that the suspension has unsprung mass,

Another is that washboard is rarely spaced at a uniform distance for long. Curves, hills, ruts, traffic (animals?), and embedded rocks all force us to slow down/speed up, and this speed variance changes the frequency of the washboard such that "just go fast" rarely works for long.

The same can be said for "just go slow".

Having 20" of suspension travel like a desert racer -- along with meaty high volume low pressure tires -- is the answer. Might eat into MPG a bit tho...
 
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