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


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Old 06-18-2007, 02:04 PM   #1
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This weekend's camping trip was instructional for me. Never really used electric brakes before... At about 115-120kph, the trailer was really prone to swaying which seems to be due to weight distribution.. It might have been a little light on the tongue because my hitch was perhaps a couple of inches too high but it's not clear that should really be the problem... As for weight, we only had a small kids bike on the rear carrier, empty black/grey/fresh water tanks, and up front, 2 propane tanks, 1 battery, food and linens... Also some linens up in the side gaucho... So, I'd say nothing unusual, as far as weight distribution... Once the trailer started to sway, I gave it a little screech with the manual lever on the prodigy and it fell back into line, but I'll really need to address the problem permanently...

The more troubling issue was the side to side rocking... On a few occasions, the trailer would start to rock left/right and not stop for a long time... I'm wondering if it's all the linens in the upper cupboards have moved the center of gravity too high in conjunction with the spring-over that was already done on the trailer... I really need to mount some shocks on that thing...

Does anyone else with a Boler 1700 (leaf sprung, with a spring over) have this experience?
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Old 06-18-2007, 03:41 PM   #2
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What kind of tires are you using?They could be the problem at higher speeds.Keep speed to under 115 kph.
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Old 06-18-2007, 04:14 PM   #3
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I'll really need to address the problem permanently...
I suspect the changing wieght distribution should start at your foot. Thats 75 mph on a single axle..

Slowing down will make a world of difference, and be far safer...
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Old 06-18-2007, 04:16 PM   #4
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Herb,

Not to be the bearer of bad news, but you've done just about everything you can do to induce sway: high center of gravity, towing tongue high, further unloading tongue weight by putting a bike carrier on the rear, loading your weight high in the trailer...

Check out this thread.

Put your heavy stuff down low. Tow level... yes, 2" high from level at the tongue makes a HUGE difference in weight distribution. Don't carry a bike of any kind on the back... the combination of carrier and bike is probably a hundred pounds, with the mechanical advantage of the axle allowing it to lift 100-200 lbs at the tongue... If you do all that, I'd bet your next trip will be a piece of cake!

Roger
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Old 06-18-2007, 06:02 PM   #5
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First thing you need to do is slow down!! Trailers in general are intended to be towed at less than 65 MPH or 110 KMH.

Item 2 what is the total weight of your trailer, fully loaded? Now weigh the tongue, you need a bare minimum of 10% of your total trailer weight here, 12% works even better. This number is not 10 or 12% of your axle weight, it is 10 to 12 % of the total weight of your axle an tongue combined. Drop the tongue of the trailer to at least level.

Once you have done this you should be in much better shape!!

Now start looking at your tires and suspension, if you have P type car tires they can cause a problem due to the sidewalls being too flexible which can induce a side to side wallowing. It is because of this that ST or light Truck tires are recommended for trailer towing. Another problem with older trailers is that the suspension components become tired, whether they be springs or rubber torsion. A different rebound value between the 2 sides of the trailer can also induce wallowing side to side.

Sorry to hear about the tough tow, but at least you found it without getting into real trouble.

By the way, don't bother with sway control devices until you have resolved the cause of the sway in the first place. Sway devices are intended to limit the sway in an emergency on a trailer that handles well in the first place.

Good luck with tracking down the problems!!
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Old 06-18-2007, 07:10 PM   #6
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I agree that weight distribution is important. To most people, this means strictly front-to-rear, and they assume more tongue weight is better... which is not true. My B1700RGH is nice and stable at 10% tongue weight (about 250 lb empty, 305 lb loaded).

Height of the load is important, too, because it makes the trailer more of a pendulum - see the next paragraph... My trailer is stock in ride height and component mountings, so I have no useful B1700 experience to add in this respect.

The side-to-side weight distribution is also important. If one side is heavier, it causes more suspension compression on that side, affecting axle alignment and starting it to lean; tire drag is greater, pulling the trailer to that side, and starting a yaw movement. Various trailers (not just this Boler model) have been reported to rock (roll side to side) and/or sway (oscillate in yaw) as a result of this condition.

The B1700RGH tends to be left-heavy, the side with the refrigerator and closet, and with the water heater over there as well the B1700SGH is probably even more prone to this problem. The result is that is rolls side-to-side at some speeds (if unevenly loaded), particularly in some crosswind conditions. This is not yaw, but since the coupler may not be at the ideal level, it is felt as side-to-side force on the hitch, and a laterally soft tow vehicle could allow that to become yaw, and thus sway.

Drag it over a highway weigh scale one side at a time, and my guess is that it will be left-heavy; redistribute some movable stuff to the right, and I expect that it will be fixed. The previous owner of my trailer warned me about this, and I have observed it myself. Yes, 115 km/h seems to be a good speed to get this going!
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Old 06-18-2007, 07:14 PM   #7
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...By the way, don't bother with sway control devices until you have resolved the cause of the sway in the first place. Sway devices are intended to limit the sway in an emergency on a trailer that handles well in the first place.
I agree that various sticky and springy linkages ("sway control devices") will mask the vehicle dynamics, making it harder to find a real solution. I don't use any (in case you haven't noticed me saying this before...)
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Old 06-18-2007, 07:29 PM   #8
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...Don't carry a bike of any kind on the back... the combination of carrier and bike is probably a hundred pounds, with the mechanical advantage of the axle allowing it to lift 100-200 lbs at the tongue...
The distance from the axle to the back bumper of a B1700, as is typical of travel trailers, is less than the distance from the axle to the coupler... maybe about half the distance or a little more. As a result, 100 lb of load at the bumper would reduce the coupler load by about half (not twice) that (say 50 lb), and increase the axle load by the total of the two (say 150 lb).

For an example...
  • start with a trailer at 2800 lb with 10% tongue weight before the bike rack, so it has 2520 lb on the axle and 280 lb on the tongue (this is a realistic moderately packed B1700).
  • add 100 lb to the rear bumper (the bikes and rack)
  • still using the 2:1 distance ratio, the new tongue weight is 280 - 1/2*100 = 230 lb
  • the new axle load is 2520 + 100 + 50 = 2670 lb
  • the resulting tongue weight is 8.6% of the total trailer weight... but started as 10%
Although the tongue weight decrease isn't huge, the balance effect appears significant. Also, since the centre of the trailer's mass is ahead of the axle, the rear bumper is quite far from that centre, so mass carried there makes the trailer more like a flywheel - harder to start turning, and harder to stop. This is bad for control.

See my later post for an updated calculation.
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Old 06-18-2007, 07:54 PM   #9
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I'm not sure how much effect the coupler height has on tongue weight. It can't be calculated unless the height of the centre of mass is known, and I have not checked my Boler at various to determine the effect. I have seen in previous discussions that others have, but for different trailers; has anyone done a B1700?

The issue of pitch attitude (nose up or down) has been discussed a number of times, most recently in Trailer Ride Attitude...., whats the correct (safest) angle? In addition to the possible causes mentioned there, I have one more to suggest which is specifically relevant to the B1700... leaf spring suspension geometry.

Lifting the tongue tilts the trailer back, and with it the leaf springs and their mounting points, changing the effective geometry. It also changes the camber and toe (for leaf spring independent suspensions), as mentioned in the other topic, but I find it hard to see enough change there to be important (although everything contributes). I suspect that the effect of the leaf geometry is less stability as the trailer is tilted back.

I had the tongue of my B1700 a little high on the last leg of my last trip, since I had offloaded all of the cargo and not adjusted the air spring pressure; it felt a little less stable. I lowered the van back to the normal height, and thus the tongue to level, and all was back to normal.
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Old 06-18-2007, 08:04 PM   #10
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The place to START is getting the right tongue weight and until you weigh it on a scale, you won't know what that weight is or even what it should be. Get thee hence to a scale forthwith!!
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Old 06-18-2007, 08:15 PM   #11
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... until you weigh it on a scale, you won't know what that weight is or even what it should be. Get thee hence to a scale forthwith!!
... but more slowly

Agreed!

Even before towing to a full scale, a bathroom scale can be used to check the tongue weight. Since the overall weight can be guessed to within +/- 10% or so, a reasonably appropriate tongue weight is already known: the trailer is 2400 lb dry, has a bunch of stuff in it so it must be at least 2800 lb, and is not supposed to be more than 3000 lb, so try 300 lb on the tongue... then go tow to the highway scale.
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Old 06-18-2007, 10:28 PM   #12
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... but more slowly

Agreed!

Even before towing to a full scale, a bathroom scale can be used to check the tongue weight. Since the overall weight can be guessed to within +/- 10% or so, a reasonably appropriate tongue weight is already known: the trailer is 2400 lb dry, has a bunch of stuff in it so it must be at least 2800 lb, and is not supposed to be more than 3000 lb, so try 300 lb on the tongue... then go tow to the highway scale.
Ok. I just checked the bathroom scale. Tricky getting the trailer in there but it just fit...

230lbs on the scale which is a bit heavy but I've just had a couple beer so who knows... The tongue on the trailer is 320lbs. Well, that's about 2feet short of the hitch where the tongue jack mounts but I figure that's close enough. Or do we contend that each wheel takes half the weight. and if we figure the wheels are 10 feet from the tongue, then my measuring 80% forward means I'm 20% over so it's closer to 300lbs?

That's roughly the same weight as towing weight... There's a 6 pack less beer on the front rack, and less potato chips/crackers in the overhead compartments... No bike in the back either.
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Old 06-19-2007, 05:00 PM   #13
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... The tongue on the trailer is 320lbs. Well, that's about 2feet short of the hitch where the tongue jack mounts but I figure that's close enough. Or ... if we figure the wheels are 10 feet from the tongue, then my measuring 80% forward means I'm 20% over so it's closer to 300lbs?
Yes. I measured my B170RGH at 128" from axle to coupler, so if the scale is measuring at 15" further back, the weight at the coupler will be (128-15)/168=88% of the scale reading (now 326 lb), or 288 lb.

288 lb might be a bit light for a loaded B1700.

Edit note: to avoid massive topic clutter, I just updated this with Herb's jack position measurement and weight at the jack, rather than adding a post, and put changed text in italics.
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Old 06-19-2007, 06:30 PM   #14
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To update my previous post...

The distance from the rear face of my B1700 bumper to the axle is 76"; from the axle to coupler is 128". That means my rough-guess calculation above can be replaced by something less approximate:
  • start with a trailer at 2800 lb (this is a realistic moderately packed B1700) with 312 lb (see above post and below) tongue weight before the bike rack, so it has 2488 lb on the axle.
  • add 100 lb to the rear bumper (the bikes and rack)
  • assume the bikes and rack are centred 10" behind the bumper (a wild guess)
  • using the 128" and 76" distances, the new tongue weight is 312 - (76+10)/128 * 100 = 245 lb
  • the new axle load is 2488 + 100 + 67 = 2655 lb
  • the resulting tongue weight is a somewhat low 8.7% of the total trailer weight... but started as 11.1% which would have been fine.
... same observation as before, but changing with each re-calculation, due to the uncertain tongue weight, and that my 2:1 length ratio guess should have been 3:2

Any more refinements? Anything not make sense in my calculation?

Edit note: to avoid massive topic clutter, I just updated this with Herb's new tongue weight measurement, rather than adding a post, and put changed text in italics.
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