towing a 17foot ... swaying and rocking .... - Page 2 - Fiberglass RV


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Old 06-19-2007, 06:37 PM   #15
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...Well, that's about 2feet short of the hitch where the tongue jack mounts...
Two feet? Isn't this the coupler-mounted jack in the photos in Boler 1700 refresh., which is only about a foot back? That would make a significant difference in the correction of the measured weight - Herb, let me know and I'll correct as appropriate. If it is the coupler-mounted jack (in the "A" at the back of the coupler), I'll have the measurement.
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Old 06-19-2007, 07:31 PM   #16
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Two feet? Isn't this the coupler-mounted jack in the photos in Boler 1700 refresh., which is only about a foot back? That would make a significant difference in the correction of the measured weight - Herb, let me know and I'll correct as appropriate. If it is the coupler-mounted jack (in the "A" at the back of the coupler), I'll have the measurement.
Ok. So here we go...

(1) Tires are ST205/75r15. Each tire is at 48PSI (max 50).

(2) The tongue jack was traded out because the stock one in the A was hitting the spare tire on my tire carrier. I mounted another one further back.

I just measured again.

At the tongue jack, as yesterday, I measured 326lbs exactly. The tongue jack is 15" laterally back from the ball. (as in, not measured along the frame rail, but straight back from the ball).

I measured exactly at the ball (by sticking a piece of 1x1 inside the ball and on the scale with a piece of 2x4 to distribute the weight across the width of the scale) and got 312lbs. So 15" makes a 14lb difference. In both cases, the trailer is level (my driveway slopes, but the trailer is level for the purposes of the fridge).
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Old 06-19-2007, 08:00 PM   #17
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I updated a couple of posts with the new numbers.

The tongue weight as a percentage of trailer weight is still an estimate, because the total trailer weight is not yet known, but a couple of observations:
  • The tongue weight is really sensitive; typical travel trailers carry so little of their weight on the hitch that small changes are proportionately big. In a car or truck, moving a couple percent of the total vehicle weight between the axles is no big deal, because it is a small fraction of what each carries; in a trailer, the slight shifts don't matter to the axle load, but do to the tongue weight.
  • Although 8.7% tongue weight is a little low, I can't believe that it should be a problem... it is double the fraction carried by some trailer tongues in Europe. They may not be pillars of stability, but 8.7% should not inherently be a problem.
The tires are ST-rated, C load range, properly inflated, stock width and aspect ratio, and one inch oversize in wheel diameter. I assume that we can rule out the tires as a source of problems...

Finally, when I compensated for jack position I get a lot more difference than Herb actually measured. The difficulty of getting accurate and repeatable measurements? An unintended shift in coupler height causing a load shift forward? I messed up something in the calculation? Does anyone care? Time to sign off for today...
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Old 06-19-2007, 10:01 PM   #18
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I updated a couple of posts with the new numbers.
[*]Although 8.7% tongue weight is a little low, I can't believe that it should be a problem... it is double the fraction carried by some trailer tongues in Europe. They may not be pillars of stability, but 8.7% should not inherently be a problem.[/list]The [b]tires are ST-rated, C load range, properly inflated, stock width and aspect ratio, and one inch oversize in wheel diameter. I assume that we can rule out the tires as a source of problems...

Finally, when I [b]compensated for jack position I get a lot more difference than Herb actually measured. The difficulty of getting accurate and repeatable measurements? An unintended shift in coupler height causing a load shift forward? I messed up something in the calculation? Does anyone care? Time to sign off for today...
Some other factors, if we're fine tuning the numbers... 10 inches for the bike/bike rack is probably pretty close. The spare tire is now on top of the bumper, and the bike rack straps right up against the spare. The kids bike (it's maybe about 25ish pounds)goes almost right up against... So maybe closer to 6 inches. I'd estimate bike rack and kids bike at about 50 pounds, max.

When travelling there, we had a cooler on the front rack that is not there now. One of those stainless coleman jobbies. It had 12 bottled water, 12 cans of club soda, and 15 cans of Keith's... That's 13.3liters which is, say, 13kg plus another 5kg for the cooler. So say another 18kg or 40pounds 27 inches from the hitch. That probably helps boost things a bit...

So, if we're close to eliminating weight distribution, eliminated tires, then that leaves hitch height and speed... I'm having trouble accepting speed but I do acknowledge I don't have an actual _need_ to do 120kph (the highway in question is one of those where everyone's doing 130kph and if you're doing less than that you get the googly eyed stares)... I confess to wanting to see what my recently rebuilt turbo diesel could do...
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Old 06-19-2007, 10:14 PM   #19
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It's the speed dude.

Even if we count out everyone else's experience, here's what we get:

You travel at a buck twenty, trailer starts to sway.
You slow down, swaying stops.

Speed seems to be the variable causing your grief.

It's like death-wobble on a Jeep, or other vehicle with solid front axle. A little slop in the system goes a long way, and speeding up exacerbates the problem

You could spend a million bux, and never sort out the problem of an old trailer swaying behind the rig, or you could drop a couple km's, and never see the problem again.
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Old 06-19-2007, 11:04 PM   #20
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Well Herb, on my 13' I run a tongue weight of 12-15%, "P" rated tires at 36 PSI, and have had no sway problems even at speeds up to 85 MPH......I also run "P" tires on my 17' and never had any problems with it either, although I`ve never had it up the the higher speeds.....one day I went out on the highway near here when there wasn`t much traffic and even tried to enduce a sway condition at about 45 mph but it would just follow my trucks actions and when I stopped the swerving the trailer did also....I tried this to see how the auto tires would react.....not sure now what my tongue weight is on the 17' but think it`s about 12% when ready for travel.....maybe will scale it this week, even though am not going to use it till fall time I guess.....will use the 13' in a couple weeks to go West ,(Edmonton and Canmore), and then back to Macklin Sk., for the Bolerama.....will see how things will work out....Benny
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Old 06-20-2007, 07:07 AM   #21
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Yeah. I never had sway problems on my 13 either ... Maybe Paul's got something... The 1700 is leaf sprung and as such, has spring bushings and so forth with slop...
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Old 06-20-2007, 01:11 PM   #22
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If I had an old pickup truck which wobbled all over the road at 120 km/h, I would probably not decide that the correct fix was to only drive at less than 120 km/h.

I don't think we've eliminated weight distribution as a problem source for Herb's trailer. What about the side-to-side issue? The resulting rocking will occur at lower speeds with mine and the other B1700RGH which I test-pulled, depending on the severity of the imbalance and triggering conditions such as sidewinds; setting an arbitrary speed limit does not ensure that the problem is gone.
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Old 06-20-2007, 03:35 PM   #23
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Sway gets worse as speed increases, but since sway is occurring at reasonable, if somewhat high, highway speeds, something is wrong. Slowing down is only a temporary fix for a basic problem.

ALL trailers sway, the thing is to reduce that sway to acceptable limits, and swaying at legal automotive speeds is NOT acceptable, even if it isn't a good towing speed. It means that even at lower speeds if you hit high winds, do a violent maneuver or skid on a loose or wet surface, you will be far more likely to lose control.

As suggested above, side-to-side weighings should also be made.
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Old 09-01-2007, 08:14 AM   #24
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It's been a summer of periodic experimentation and elimination of variables...

* I've done a trip with my second tow vehicle which has a frame mounted hitch receiver that is lower than the bumper mounted hitch on my diesel. This dropped the tongue of the trailer down and resulted in a trailer that was perfectly level (visually, anyway)... Still swayed in the same manner. On the way back, we kept all linens and heavy blankets down on the gaucho instead of overhead. Same swaying tendency.

* Another trip with the primary tow vehicle, but with a drop receiver making the trailer level. Also welded on some shocks (Rancho 5119's; because I had some spares) to hopefully reduce the pendulum effect and therefore maybe the swaying. Experimented at various speeds. I could induce swaying relatively easily at 105kph. This was with 2 bikes on the back, 120l of water in the tank, a 70lb toolbox on my front rack (to compensate for the bikes), a cooler full of water, beer, juice, and ice (maybe 100lbs) on the front rack.

After the return of our final camping trip this season, I took the trailer to the weigh scale but sadly, I didn't re-read this thread before doing so and it didn't even occur to me to do the side to side weighings... I am dumb.

The results of the weigh-in are thus:

* Truck axles on scale with trailer connected (trailer off the scale)
** 2720 KG (5996lb)
* Trailer axles on scale connected to truck (truck off the scale)
** 1340 KG (2954lb)
* Truck axles only, trailer parked off to the side
** 2580 KG (5688lb)

Therefore:

* Trailer only
** 5996 + 2954 - 5688 = 3262 lbs
* Truck and Trailer
** 8950 lbs
* Tongue weight
** 3262 - 2954 = 308 lbs

Description
-----------

Fresh water tank, grey water tank, black water tank all empty
Jakob's bike and Shari's bike on rack
Herb's bike inside.
Cooler mounted but empty
Toolbox on tongue
half tank of diesel


-------

So the tongue weight is a little low relative to the trailer weight but the differences (empty cooler and empty fresh water tank) would have increased the weight at the front of the trailer...

The shocks did prevent the pendulum effect when passing so that was a net win, in my opinion. I heartily recommend installing shocks if you have a leaf sprung trailer (possibly even a torsion axle). The Rancho's are not pre-loaded shocks so they do not help to offload the suspension. It's not clear to me whether that's a feature or not... I figure it probably isn't hurting.

Maybe I should also spend a minute to define what I observe as swaying. If we're driving along and my wife (generally of weak constitution) puts her hand on her tummy and says "we're swaying" with a quick glance at the speedometer; then I can detect that the tail is indeed wagging the dog, albeit slightly (not the death wobbles)... A bit of acceleration will dampen the movement or a quick pulse of the brake controller will cease the sway as well... If I don't do anything (maintain current speed) the sway does eventually stop, say, after 10 oscillations or so... But the consternation of the passenger side sway monitor is enough to prevent me from waiting and swift action is required.

We were able to have a fairly comfortable un-eventful drive home by keeping speed at about 100kph (on a highway where the legal limit is 110kph and everyone does 120-130kph including the semi's hauling fuel in b-trains).

Maybe I'll do some side to side weighings today before I winterize the Boler.
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Old 09-01-2007, 10:46 AM   #25
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I can't tell from Herb's latest description if the sway is in roll or yaw. With my Boler the side-to-side imbalance causes a rolling oscillation which not affected by trailer brakes or acceleration. While I look forward to hearing the results of a side-to-side weighing, I suspect from these observations that side-to-side imbalance is not the problem, or at least it is not affecting Herb's trailer the same way as mine.

The hitch weight fraction, while low by North American standards, is sufficient by Euro standards. Are the masses at the ends of the trailer (such as the bikes on the back) making the pendulum effect (polar moment of inertia) too high for the low-tongue-load configuration? My tongue weight is similar, but typically with 10% lower overall trailer weight. Even with water in the fresh tank (behind the axle in my case, decreasing hitch weight) I don't have a yaw problem.
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Old 09-01-2007, 10:53 AM   #26
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Herb, a couple of photos of the shock mounting would be interesting, if you get a chance.

Most shock absorbers are gas-charged now. The twin-tube designs - which include the Monroe units on my Boler - have very little force tending to extend them, at least compared to the trailer weight. I did not observe any height increase when I installed them.

The single-tube designs (probably rare in trailers) use higher gas pressure, and exert enough force to cause a visible increase in ride height on some cars; however, it might still not be noticeable on a trailer with a relatively high weight for the shocks, and relatively stiff springs for the weight.

Essentially, gas shocks act like small air springs added to the suspension, and I would not be concerned by their addition to a typical trailer suspension.
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Old 09-01-2007, 01:17 PM   #27
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Sorry if my descriptions are a little ambiguous... When I say "pendulum", I mean 'roll' in aircraft terms.... That problem seems to have disappeared with the mounting of the shocks... I'll take photos later today and append them to this thread... I'll warn now that the mount isn't particularly pretty because I just used what I had lying around...

I just did the best side to side weighin that I could do given the highway scale. One side of the scale platform was almost right up against the curb so I could only weigh the right side of the trailer... I had my son with me and had already moved the toolbox into the back of the truck from the front of the trailer. I also removed the bikes... So in retrospect, I may have made this whole exercise worthless...

Here are the numbers regardless...

Truck axles with trailer attached: 2790 KG (6150lbs).
Trailer axle attached to truck: 1250 KG (2755lbs).
Trailer axle, right tire only: 560KG (1235lbs).
Truck axles, right side only: 1360KG (2998 lbs).

There was a long lineup of trucks and it started raining so I didn't much feel like unhitching the trailer and taking the truck through by itself but I fear that would have been the missing piece of the puzzle...

So it seems like the trailer either lost 500 pounds (highly unlikely) or there is actually a significant left/right difference... I'd say the trailer lost 200lbs at best... My bike is about 25lbs, Shari's about 30, Jakob's about 30, the carrier about 20, and the toolkit about 70.

Brian: What I meant by preloaded shocks was they do not extend on their own. The shocks I put on my truck to replace my old Rancho's were spring loaded so I had to use a ratchet strap to shrink them so I could get them onto the mounts... These Rancho's stay in whatever position you put them.

The 'sway' I'm concerned about is 'yaw'.
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Old 09-02-2007, 01:27 PM   #28
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What I meant by preloaded shocks was they do not extend on their own. The shocks I put on my truck to replace my old Rancho's were spring loaded so I had to use a ratchet strap to shrink them so I could get them onto the mounts... These Rancho's stay in whatever position you put them.
The "spring loaded" shocks are gas-pressurized; Herb's current shocks are apparently not. Gas pressurizing is good - it helps prevent foaming of the fluid - and it is now normal, but I suppose it is not necessary, especially in a trailer suspension which moves very little. Hopefully, the shocks are close to vertical, since highly inclined shocks particularly benefit from pressurization.

If a ratchet strap was required, those Ranchos may have been a high pressure single-tube design; I've installed those, and it can be annoying. The Monroes on my Boler are low pressure twin tube units, which I can easily compress by hand for mounting.
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