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.