Questions About Sway Control

[wkpoor]

I have pulled various types and kinds of trailers my whole life but never has any had sway control. Many talk highly of using them. I got to thinking how I've never seen sway control on a boat trailer and they typically have light tongue loads compared to utility trailers. My own boat weighs 4k and I can pick up the tongue and over many miles its never once tried to sway. That TW should be 4-500lbs according to trailer Hoyle. Also I've really never even experienced sway on any trailer. However all my trailers do have the axles far back which makes me wonder if axle placement is a big factor on sway potential and even more so than TW. What I see on travel trailers going do the road is they put the axles too far forward, obviously to limit TW for the majority of SUV's pulling these days. If the axles were back a little wouldn't that solve the problem?

 

[KeithInSpace]

I'm not sure about the SUV theory...different manufacturers make trailers different ways for reasons probably unrelated. The only thing I can say about SUVs is that they are generally SHORTER (in wheelbase) than pickups, perhaps making them more prone to sway. Dunno about that one.

Example: My Leonard trailer is a 20' dovetail...18' deck with 2' on the tail. By my estimation, the axle placement relative to the rear of the trailer is exactly as it is on their 16' dovetail...14' deck with 2' on the tail. As if it was set there by template. I don't mind it one bit EXCEPT that I need to be very careful how I load the trailer. My first 6 CY load of mulch was evenly distributed along the deck...BIG MISTAKE. I can easily carry 6 CY, but I leave the front of the trailer EMPTY with the entire pile over the axles.

I'm not 100% sure what instigates trailer sway, but the first line of defense is proper loading (for proper tongue weight) AND CARRYING A LEVEL TRAILER. Not sure how much truth there is to the theory, but I heard carrying a "low" tongue promotes sway more than a "high" tongue. I carry a "level" tongue.

I also think sway, being a form of harmonic motion, has a lot to do with trailer frequency, tire load, and roll center. My theories on the matter:
--A higher-loaded trailer (high COG relative to trailer width...think 4' wide trailer carrying 2 refrigerators) is more susceptable to sway...high roll-center.
--A shorter trailer is more susceptible to sway...higher frequency swing.
--A trailer with overloaded tires or improperly inflated tires are more susceptible to sway...allowing hubs additional "roll" within tire carcass.
--A trailer made out of an old pickup bed is more susceptible to sway...all of the above...higher roll center, improperly soft suspension, probably improper (P or LT) tires, and shorter trailer than most.

For all these reasons, I don't think boat trailers are particularly susceptible to sway...they're quite long and the boat's COG is generally low in the hull, between the trailer's wheels. I towed around a 24' Bayliner and the trailer was HUGE...very long. Assisted in launching by keeping the tires of the tow vehicle out of the water. NEVER had an issue with ANY type of sway on that trailer.

My travel trailer is totally different. It is slab-sided and has things like the A/C unit mounted to the roof. Other than the weight of water/sewer tanks and the frame itself, I'd say the weight of the structure and trailer innards are fairly evenly distributed vertically inside and outside the trailer. And it can catch a cross-wind much easier than a boat.

Lastly, 5th wheels, carry a huge amount of tongue load relative to bumperpulls. Therefore, their wheels are MUCH further back than comparable bumperpulls. This shifts their harmonic motion frequency FAR TOO LOW to ever occur in normal circumstances. This is why they, nor Big Rigs for that matter, have sway control as an option.

My thoughts in conclusion: Boat trailers generally don't need sway control. Most types of travel trailer can benefit from sway control. For utility trailers, it depends on a huge variety of circumstances...I don't run sway control on mine, but I will in the near future.

 

[zzvyb6]

Yes, but the 'rule of 10%' is supposed to apply to all trailers. Your boat is unusual in that the F/A center of gravity is back farther that it would be with a utility trailer carrying lawn mowers or roofing or bricks, etc. Also, your boat and trailer doesn't change its c.g loaction that much when you add fuel, toys and other gear. This distance change relative to the trailer wheelbase is pretty small. There are a few other factors that contribute to the stability of a boat trailer combiination: spring geometry, good tires with large load capacity, decent towing vehicle. These factors are not ALWAY in place for utility and travel trailer combinations. Obviously, the travel trailer weight, wheelbase, tires and geometry effects need to be augmented by hitch moment restrictors (equilizing hitches, friction and load seeking sway controls).

A multi-axle trailer has more inherent stability because the tires scrub in a yawing mode. This stabilizes the unit combination. You can even run a multi-axle trailer at practically zero tongue load.

And yes, there are still those that grease their balls and sway control plates. They eliminate or reduce the friction that is wanted for yaw damping.

5, 4, 3, 2, 1 ...

Now let's hear all the anecdotal squak about the advantages of greasing your stuff. It ain't so, folks. Take your trailer, set it up for ZERO tongue load, drive 60 -65 mph or so to determine the speed at which the trailer starts cycling. Then grease your hitch ball and call us from the hospital with the speed at which the trailer went out of control. It's probably gonna be 5 - 10 mph less.

That's why we run tests, thats why we do computer analysis, that's why there are SAE standards. Darwin has played along with us on this, too.

 

[KeithInSpace]

I grease my ball. I have this fear of it someday binding on some bump and something breaking.

He who greases the plates of a sway-control device, however, is an idiot.

[Soapbox] Very generally speaking, I agree with your zero-tongue-load, multi-axle trailer example. Folks don't seem to get just how little 500# of tongue weight is relative to a 5,000# load...it is very, very little. The tongue weight is crucial simply because the tongue is designed to interface with positive, not negative, pressure. Therefore, the tongue mechanism is not designed to withstand repeated shock load of an evenly loaded tongue or the constant upward pressure of a negatively loaded tongue. Not to mention that you're literally LIFTING the wheels upward on your tow vehicle either on bumps or constantly...very bad thing.

I'd put GOOD MONEY on a bet that at least 4 in 5 trailers (yes, 80%) have an improperly loaded tongue, most being overloaded RELATIVE TO THEIR PAYLOAD.

Good example: 10k# capacity trailer (2,200#) with 5k# payload over the axles, total 7,200# with 800# tongue load.

Bad example: 10k# capacity trailer (2,200#) with 3k# tractor driven to the front rail. Total load is less (5,200#), but probably over 1,000# of the tractor and 500# of the trailer are on the tongue...nearly 30% of the load.

I'll stand on the firing range with you, brother. I KNOW where I see most tractors, skidsteers, ZTRs, lawn mowers, refrigerators, and any other amount of bounty positioned on trailers...all the way to the front, nearest the tongue. [/Soapbox]

I'd advocate the use of sway control on most any trailer except boats. Can't hurt...

AND FOR THE LOVE OF PETE, DON'T GREASE THE PLATES!!!

 

[Reg]

Fun, fun, fun...
As I understand it the trailer stability issue is one of where the center of mass is relative to the area of support.
Simple to understand as a static model; if a plumb line dropped from something's center of mass falls outside the area of support, guess what ? Yeah, it falls over.

The tongue load guideline is just a simplification to tell you where the center of mass needs to be, i.e. no farther back than 90% of the distance from the coupler to the axle (single axle for simplicity).
This puts the center of mass somewhere in that triangle of two wheels and a coupler.

At ZERO tongue load you would have the load balanced over the axle - which would be as unstable as a teeter-totter.
At 50% tongue load the center of mass would be 1/2 way between the coupler and the axle - stable like a bridge, but unrealistic for other reasons.
For one it would be a bit too close to the sides of the support triangle.
Somewhere in between these extremes are gooseneck and 5th wheel trailers and many of us know how stable those are.

BTW, it is sometimes HARD to get people to agree that a tandem axle trailer should have it's center of mass AHEAD of the front axle's center line, but if you do the measurements you will soon see that even on a short horse trailer it is so for tongue loads over about 11%.

One other thing on tandem axles, if the ball height is too low the rear axle will not be carrying it's full share, i.e. the area of support will be shortened and moved forwards, where it will be closer to the center of mass and hence the trailer will be less stable.

Then there is the whole DYNAMIC stuff (-:
Boat trailers are built with a design goal of "ease of launch" - well, you would hope so ?
So they carry the load (boat) as low as practical.
A low center of gravity is GOOD for trailer stability.
The tongue on a boat trailer is often quite long, so for any given distance the center of mass might be ahead of the axle there will be a lighter tongue load.
Example; sail boat trailers for boats with deep keels often have extension bars for launching.
When attached the tongue load might decrease by 30 or 40%, but the center of mass is (almost) in the same place.
A lot can also be done with castor, camber, toe in/out, so it isn't ALL about tongue load.

Don't worry too much about this, but horses MOVE their weight (1,000 or more) in the trailer and their individual centers of mass are quite high.
Horse trailers have a similar design goal; ease of LOADING.
The floor is therefore typically as low as practical, for loading as well as to keep the (shifting) weight low.

 

[Diamondpilot]

In a simple answer, yes axle placement has everything to do with sway. I have towed all my life. Even went to take my drivers test with a trailer in tow but had to drop it in the lot before the examiner would start the ride, and never used a sway control and for that matter a WD hitch. Of course we always had big trucks like F-350's around that simply did not need it even with 20% tongue load on a 15,000# trailer.

Boats tow like a dream in most cases and the ones that did not had too little tongue weight.

Chris

 

[VitaBene]

Yes, but the 'rule of 10%' is supposed to apply to all trailers. Your boat is unusual in that the F/A center of gravity is back farther that it would be with a utility trailer carrying lawn mowers or roofing or bricks, etc. Also, your boat and trailer doesn't change its c.g loaction that much when you add fuel, toys and other gear. This distance change relative to the trailer wheelbase is pretty small. There are a few other factors that contribute to the stability of a boat trailer combiination: spring geometry, good tires with large load capacity, decent towing vehicle. These factors are not ALWAY in place for utility and travel trailer combinations. Obviously, the travel trailer weight, wheelbase, tires and geometry effects need to be augmented by hitch moment restrictors (equilizing hitches, friction and load seeking sway controls).

A multi-axle trailer has more inherent stability because the tires scrub in a yawing mode. This stabilizes the unit combination. You can even run a multi-axle trailer at practically zero tongue load.

And yes, there are still those that grease their balls and sway control plates. They eliminate or reduce the friction that is wanted for yaw damping.

5, 4, 3, 2, 1 ...

Now let's hear all the anecdotal squak about the advantages of greasing your stuff. It ain't so, folks. Take your trailer, set it up for ZERO tongue load, drive 60 -65 mph or so to determine the speed at which the trailer starts cycling. Then grease your hitch ball and call us from the hospital with the speed at which the trailer went out of control. It's probably gonna be 5 - 10 mph less.

That's why we run tests, thats why we do computer analysis, that's why there are SAE standards. Darwin has played along with us on this, too.

The below is from Reese's site:
What kind of maintenance do I need to do to the weight distributing hitch
WDH and sway controls?

Lubricate the ballmount sockets and spring bar trunnions to prevent rapid wear. When hooking-up, place one drop of oil on the top and a second drop on forward side of upper trunnion. Place a third drop on the rear side of lower trunnion before inserting trunnion into ballmount. Use a heavy oil such as "REESE ON THE BALL". Don't forget to lubricate the hitch ball with one or two drops also. Trunnion should be lubricated each towing day. It is not necessary to unhook the spring bars however, as there are two oil holes in the ballmount top plate for upper trunnion lubrication. Lubricate lower trunnions with one drop at contact point between trunnion and lower socket. Excess oil, dirt, and grit should be wiped out whenever trailer is uncoupled.



Can I grease the Dual Cam Sway Control (DCSC)?

Do not grease the cam and cam arms. The Dual Cam was designed to use metal-to-metal friction. Heavy greasing of the cam and cam arm surfaces with affect performance. If noise is offensive, a very light coating of lubricant, such as Vaseline, may be used. Tongue weights over 1,200 lbs. may require a light coating of grease to reduce friction and prevent excessive wear. The Dual Cam Sway Control DCSC is not to be lubricated on the cam arms when the tongue weight is under 1,200 lbs. Instead you will want to apply a thin coat of a petroleum jelly, such as Vaseline. This will act as a poor lubricant, but works well to dampen the sound. For trailers with over 1,200 lbs. tongue weight you should apply a couple of drops of an 80/90 gear lube to the cam arm to prevent excessive wear caused by the increased tongue weight.

I don't want to get in a big argument over the zero tongue load but unless that trailer is loaded perfectly over those multi-axles, you will never make it to 65 MPH. Boat trailers can run only a few percentage points on the tongue where a tilt deck equipment trailer may be closer to 15%.

 

[wkpoor]

Boat trailers can run only a few percentage points on the tongue where a tilt deck equipment trailer may be closer to 15%.

Tilts also have axle placements in the 45-50% range which makes sense why they would require more TL. Landscapers are closer to 60% and my deckover looks to be 65-70%. My boat trailer is easily 80%. I have thought for years the math on tonque load should include distance from the hitch to axle/axles center line. Further the distance the less TL required to achieve good track. Just my opinion no fact here.

 

[Bird]

I have pulled various types and kinds of trailers my whole life but never has any had sway control. Many talk highly of using them. I got to thinking how I've never seen sway control on a boat trailer and they typically have light tongue loads compared to utility trailers. My own boat weighs 4k and I can pick up the tongue and over many miles its never once tried to sway. That TW should be 4-500lbs according to trailer Hoyle. Also I've really never even experienced sway on any trailer. However all my trailers do have the axles far back which makes me wonder if axle placement is a big factor on sway potential and even more so than TW. What I see on travel trailers going do the road is they put the axles too far forward, obviously to limit TW for the majority of SUV's pulling these days. If the axles were back a little wouldn't that solve the problem?

I, too, have been pulling trailers of all kinds since I was 16 years old and started with a little utility trailer and a clamp-on bumper hitch on a '46 Chevy 2 door sedan. Since then, it's been an assortment of utility trailers, boats, and RVs. I never had a sway control on anything except the travel trailers, but I would not pull a travel trailer without one. In our years of RVing, I lost count of the number of people I talked to who wrecked their first travel trailer because the salesman didn't tell them about sway controls, but you can bet they had one on their next rig. Axles too far forward on travel trailers? Yes, unless you use a sway control. Having the axles farther forward is partly to keep the tongue weight down, but it's also to make the rig turn shorter; i.e. turn in less space when backing. Having to back into campsites used to be standard, but pull through sites are more and more common now.

the 'rule of 10%' is supposed to apply to all trailers

Well, sorta. It's not really a "rule" but a general guideline for utility trailers, rental trailers, and travel trailers, and it's actually 10% to 15%. An extra long tongue such as many boat trailer have, or axles extra far back can certainly be a reason to not have to follow that "rule".

 

[Raw Dodge]

A boats engine and outdrive is its heaviest component short of the hull,they are low and all the way at the stern.Boats need as little as 5%-8% to tow nicely,they are much different than utility or enclosed trailers.Sway control shouldn't be necessary in most cases.If you need sway control even with 12% tongue weight,then it is likely your trailer is poorly designed,your trailer tires are incorrect,or the tow vehicle is marginal for the load being towed.Ive towed many trailers behind a lot of different rigs,and what i see most is not enough tongue weight and improper trailer loading as the most common cause of sway.The comment about sway control couldnt hurt isnt true at all,friction sway controls can be dangerous.Once a trailer sways,the fricion sway will try to keep the rig in the swayed position as hard as it tried to keep it from going there before the friction was overcome....The only sway control I would use is the Pro Pride or Hensley arrow.The patented design turns the rig into a huge straight truck from the trailers tongue rearward.The tow vehicle can still act on the trailer,but the trailer cannot make the tow vehicle sway.No friction invloved,just geometry of the trapazoid system.Downside is thei nitial setup and $$,in addition to needing a very smooth brake controller with more initial ramping.

 

[KeithInSpace]

The comment about sway control couldnt hurt isnt true at all,friction sway controls can be dangerous.Once a trailer sways,the fricion sway will try to keep the rig in the swayed position as hard as it tried to keep it from going there before the friction was overcome...

I disagree. The point of a properly tensioned/compressed friction-type sway control arm is to INCREASE the harmonic frequency at which your trailer achieves sway. This is done by creating resistance to the motion at all points. Increase that frequency enough and, as a matter of physics, the possibility of sway is all but eliminated. Saying that HAVING a friction sway control arm is more dangerous than NOT HAVING a friction sway control arm is simply incorrect.

The only sway control I would use is the Pro Pride or Hensley arrow.

Having said the above, I do not disagree that these seem to be more 'comprehensive' setups that promote a positive geometry between the tow vehicle and the trialer. Getting a $2,500 hitch head wasn't the first place I looked, though. But that's not to say it isn't where I'll end up...

 

[Bird]

I agree with you, Keith. I think the key point is a "properly adjusted" friction sway control. I've not done much trailering on snow or ice, except with a fifth-wheel and one ton dually, but over 35 years ago, heard and read about over tightening friction sway controls to the point that it affected steering on slick roadways; i.e., tended to hold the trailer and tow vehicle in a straight line.

 

[KeithInSpace]

100% on the spot, Mr. Bird. If you read the side of my Reese Friction Sway Control arm, it says to tighten the device "completely", as in, until it is not possible to tighten it any further.

I did that the first time and it resulted in a "stick and slip" situation I could actually feel in the driver's seat and a horrible groaning whenever I took a turn.

I've taken to completely tightening the device, then releasing it 1/4 turn. It still has immense binding strength, but works in a much smoother fashion.

I have to admit that passing big trucks gives me a tug on the steering wheel, but I blame this on my 1/2 ton truck, IRS, and shorter truck wheelbase more than the ineffect of one of the multiple systems I have employed to better my towing safety. Passing trucks at 70 MPH notwithstanding, I have NEVER felt any issue with crosswinds, crowned roads, or any other situation where the trailer felt 'out of line'.

If I showed one of those alternate towing systems to my wife, I'd bet she'd be interested in them.

As for trailering on ice, I don't think I have the stones for that. Doesn't sound like much fun.

 

[zzvyb6]

Here's my favorite adventure. 85 mph across I-696. There are 100 50 lb bales. As you might tell from the chassis droop (or lack of it), the tongue load is pretty low. I ran it with frame level. Not a spec of sway. Hitch is clamped tight. The biggest contributor to stability in this rigging (besides the dual axles), is the short distance front the ball to the tow vehicle's rear axle. That's why a 5th wheel is probably the best system for towing a heavy trailer: when a tow angle develops, the hitch lateral force component is in phase with the other rear axle forces instead of out of phase. That's why swaying (trailer yaw velocity) begins.

The boat tug is/was actually much more oscillatory that the hay. (Frame not level). All the other engineers were worried about the transmission temperature. It was 135 degrees the whole trip. (185 parked in the driveway idling. There's a driver info center on Corvette that shows trans temp among other things)...

 

[Bird]

Here's my favorite adventure. 85 mph across I-696.

Yep, that's unusual enough to attract attention. I used to attract attention myself when I went fishing pulling my Dad's 16' boat with a 35hp Evinrude behind my 1962 Austin-Healey Sprite. Everyone who came up behind me was anxious to go around, even when I was driving the speed limit or more, because from the rear, it appeared the boat and trailer were going down the road alone. And I usually drew a few onlookers at the launch ramps waiting to see if I was going to be able to pull the boat out of the water. I never had a problem, though.

 

[Bird]

I have to admit that passing big trucks gives me a tug on the steering wheel

I've never pulled a travel trailer, except fifth-wheels, that didn't feel that tug, and it usually scares new RVers.

For those who have never pulled a travel trailer . . .. When a big truck passes you, as it goes by, it will feel as if something pulled the front of the trailer and rear of the car/truck you are driving toward the truck. It can be quite a scare for a novice, and some will almost instinctively hit their brakes, which, of course is the worst thing you can do. You soon learn that the best thing to do is nothing. It's just a momentary thing that will be over with before you know it if you don't panic and do something foolish.

Of course if a trailer does get to swaying or fishtailing, again a novice is likely to hit the brakes, and wreck out. The most effective way to stop the fishtailing, assuming it's a trailer with brakes, is to manually apply the trailer brakes, while not applying the foot brake. In fact, you can even slightly depress the accelerator pedal if you wish and pull everything back straight.

 

[KeithInSpace]

For those who have never pulled a travel trailer . . .. When a big truck passes you, as it goes by, it will feel as if something pulled the front of the trailer and rear of the car/truck you are driving toward the truck. It can be quite a scare for a novice...

Danger...Engineering Content: pv=mrt. All else being equal (mass and temperature on the right side, specifically), pressure MUST react inverse to velocity to maintain equality in the equation. The velocity between a rig and travel trailer (tall flat sides) increases, especially when passing the "wake" at the front of the rig. The resulting small decrease in pressure over the large surface area of the travel trailer gives it a VERY distinct and definite "tug" TOWARD the rig. While the effect is brief (as Mr. Bird says), it is quite freaky, to say the least.

Different tow vehicles react in different ways.

In a 5th wheel, you don't notice the effect at all. This is because the kingpin is directly over the axle. I'll bet you money, though, that the trailer DOES get an inch or two closer to the rig, although you can't feel it.

In a bumperpull, it literally pulls the bumper toward the rig, forcing a steering correction to "straighten" the tow vehicle.

In my brother's F350 diesel club-cab, long bed dually (long wheelbase, solid rear axle, very little sidewall give) the effect is somewhat negligible. As I previously mentioned, his wife recently drove that truck 1,500 miles through mountain passes with trailer behind.

In my truck (LT tires in back, IRS geometry in back, shorter wheelbase, less overall weight) the effect is VERY noticible. I am experienced, so I'm OK with it, but you need to be awake and alert.

As Mr. Bird mentions, if you hit your brakes hard at that very moment, there is an "angle" between the trailer and tow vehicle...therefore, the risk of a difficult-to-control maneuver (or possibly jack-knife) at that instant is distinctly increased.

 

[wkpoor]

I never thought about it before but a combination of long wheeel base truck
( ie most cargo vans) and trailer with axles far back would make for a real stable combination. Guy here at work said he feels vans are the best BP tow vehicles because wheel base and weight distribution.

 

[VitaBene]

I never thought about it before but a combination of long wheeel base truck
( ie most cargo vans) and trailer with axles far back would make for a real stable combination. Guy here at work said he feels vans are the best BP tow vehicles because wheel base and weight distribution.

I have heard the same but never towed heavy with a van. A buddy tows a decent sized trailer with a short bus and it does good but perhaps the stripper pole gives it stability!

 

[wkpoor]

I have heard the same but never towed heavy with a van. A buddy tows a decent sized trailer with a short bus and it does good but perhaps the stripper pole gives it stability!

I'm not sure what tow heavy is but I pull a 14K deckover with mine and I feel it does well. Sure could use more motor at times though but it gets the job done and for a fraction of the price. My FIL wheened me over several yrs ago from PU's and I've yet to go back. If the big 2 would just offer them in 4WD I can't imagine sales not doubling. If and when I get another PU it won't be 2500/250 or 3500/350. I'll go for 450 or 550. Here again I'll bet those can be had for less money and why not have more for less.