On the road
How likely is your trailer to sway?
There is no published sway index, so everything on this page is structured convention rather than a standard. What is not convention is the physics: a trailer pivots at the ball, and every factor below either lengthens that pendulum, reduces the damping, or adds an input.
The single most useful thing here is the response, and it is counterintuitive enough that it is worth knowing before you need it.
Score your own conditions
Moderate risk. Tongue weight is right at the 10 percent floor with no margin.
| Figure | Value |
|---|---|
| Tongue weight percentage | 10.0% |
| Trailer length to wheelbase ratio | 2.3 |
| Speed | 62 mph |
| Sway control fitted | no |
| Risk score | 32 of 100 |
Shown with the example figures above. Change any field to run your own numbers.
The working
Rule of thumbthe dominant term is tongue weight percentage tongue % = tongue weight / loaded trailer weight ratio = trailer length x 12 / tow vehicle wheelbase below 10% tongue weight is the sway condition, regardless of everything else
There is no published sway index. This is structured towing convention. Widely taught towing convention rather than a published specification. It is a good starting point and it is not a rating.
Fix the loading first, then this
A scale tells you the tongue weight, which is the cause. Sway control damps the symptom. Both are worth having, in that order.
Equal-i-zer 4-point Sway Control Hitch, 16,000 lb
$745.35 Published ratingsThe top of the Equal-i-zer range at 16,000 lb and 1,600 lb of tongue weight. Worth checking your receiver rating before buying it, because very few receivers carry a weight distributing rating this high.
Best for: The heaviest bumper pull trailers, behind a truck with a Class V receiver.
Check price on Amazon
Equal-i-zer 4-point Sway Control Hitch, 14,000 lb
$688.83 Published ratingsThe same four point design rated for a 14,000 lb trailer and 1,400 lb of tongue weight, which is the band most large travel trailers land in once they are loaded with water.
Best for: A large travel trailer behind a three quarter ton truck.
Check price on Amazon Equal-i-zer 4-point Sway Control Hitch, 6,000 lb
$624.46 Published ratingsThe light end of the range, at 6,000 lb and 600 lb of tongue weight. Spring bars that are far too stiff for the tongue weight ride harshly and distribute badly, so sizing down to this one on a small trailer is the correct move rather than a compromise.
Best for: A smaller travel trailer where the 1,000 lb bars would be badly oversized.
Check price on Amazon Equal-i-zer 4-point Sway Control Hitch, 10,000 lb
$552.69 Published ratingsFour points of friction sway control built into the hitch itself rather than bolted on beside it, so there is no separate sway bar to disconnect before a tight turn or a wet ramp. The sway control works in both directions from the moment the bars are seated.
Check before buying: The four point design is audible. A rhythmic creak on slow tight turns is normal for this hitch and not a fault, but people who have not been warned about it return them.
Best for: A single or tandem axle travel trailer up to 10,000 lb where you want one part doing both jobs.
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Sherline LM 1000 Trailer Tongue Weight Scale, 1,000 lb
$189.90Sherline is the scale the towing community actually uses, and a 1,000 lb capacity covers most travel trailers. Hydraulic, with no batteries to be dead when you need it.
Best for: A trailer whose tongue weight is under 1,000 lb.
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Sherline LM 2000 Trailer Tongue Weight Scale, 2,000 lb
$189.90Double the capacity for the same money as the LM 1000, which makes it the sensible default unless you are certain your tongue weight is low.
Best for: Most travel trailers, with headroom for a heavier one later.
Check price on AmazonEvery rating shown is the manufacturer's own published figure. The rating on the part you receive is what governs, and your own door jamb sticker governs everything above it.
What actually causes sway
Low tongue weight is the dominant cause and the one entirely under your control. Everything else changes how bad it gets once it starts.
Rule of thumb Widely taught towing convention rather than a published specification. It is a good starting point and it is not a rating.
| Factor | Why it matters | What to do |
|---|---|---|
| Tongue weight under 10 percent | The dominant cause. A tail-heavy load lengthens the pendulum and reduces the weight steadying it. | Move cargo ahead of the trailer axle and re-weigh. |
| Long trailer, short wheelbase | Less leverage for the tow vehicle to resist yaw. | Slow down and make sure tongue weight is at the heavy end of the band. |
| Tall slab sides | More area for a gust or a passing truck to push against. | Anticipate trucks and gusts, and reduce speed in wind. |
| High speed | Energy in the oscillation rises sharply with speed. | Slow down. Most ST tires are speed rated to 65 mph anyway. |
| Worn or soft tires | Sidewall flex adds lag between input and response. | Set cold pressure to the sidewall maximum and check the date code. |
| No sway control | Nothing damps or resists the oscillation. | Fit friction or cam sway control once the loading is right. |
Fix the loading first. Sway control and weight distribution give you back the ability to correct, but neither changes where the trailer centre of mass sits.
What to do when it starts
- Ease off the throttle. Do not accelerate and do not lift abruptly. Let the speed come down smoothly.
- Hold the wheel straight. Do NOT steer out of it. Steering corrections feed the oscillation and make it worse. Grip firmly and keep the wheel where it is.
- Apply the TRAILER brakes alone. Use the manual override lever on your brake controller, with your foot off the vehicle brake pedal. Trailer brakes pull the trailer straight behind the tow vehicle.
- Do NOT use the vehicle brakes. Vehicle brakes push the trailer forward into a jackknife. This is the instinct to override, and it is the one that matters most.
- Stop somewhere safe and fix the cause. A sway that happened once will happen again. Re-weigh the tongue and move cargo forward of the trailer axle before continuing.
Frequently asked questions
What causes trailer sway?
Almost always too little tongue weight from a tail-heavy load. A trailer pivots at the ball like a pendulum, and cargo behind the trailer axle moves the centre of mass rearward, which lengthens that pendulum while reducing the tongue weight holding it steady. A gust or a passing truck then starts an oscillation that grows rather than damping out.
What do I do if my trailer starts swaying?
Ease off the throttle, hold the wheel straight, and apply the trailer brakes alone using the manual override lever on your controller with your foot off the vehicle brake pedal. Do not steer out of it and do not use the vehicle brakes, which push the trailer into a jackknife. Then stop somewhere safe and fix the loading.
Will a sway control bar stop sway?
It damps an oscillation that has already started, or with a cam system resists the start of one, which buys you time to slow down. It does not prevent sway and it does not fix the cause. If your tongue weight is under 10 percent of the trailer weight, move cargo forward of the trailer axle and re-weigh before buying any hardware.
Does speed cause sway?
Speed does not cause it, but it determines how violent it gets and how quickly. The energy in the oscillation rises sharply with speed, so a trailer that is stable at 55 mph can be alarming at 70. Most ST trailer tires are also built to an industry speed rating of 65 mph unless the sidewall says otherwise, which is a separate published reason to slow down.
Is a longer trailer more likely to sway?
A long trailer behind a short wheelbase tow vehicle is the demanding combination, because the tow vehicle has less leverage to resist yaw. That is a reason to be careful about loading and speed rather than a disqualification. Tongue weight at the heavy end of the 10 to 15 percent band matters more on a long trailer than a short one.
Does a weight distribution hitch prevent sway?
Not directly. It restores load to the steer axle, which gives you back the steering and braking authority to correct, and that is genuinely valuable. It does not change where the trailer centre of mass sits, which is what sway actually is. Some hitches integrate sway control as well, and that is the part doing the damping.
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Researched, not professional advice. This page is compiled from published standards, manufacturer towing guides and product specifications, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are towing convention rather than published standards, and they are labelled that way wherever they appear. Nothing here overrides your own ratings. Work your payload sum before your tow rating, because payload is the limit that actually binds on most half ton trucks and nearly every SUV. Load a conventional trailer to 10 to 15 percent tongue weight and a fifth wheel to 15 to 25 percent pin weight, and never lighter: a tail heavy trailer is what starts sway. Weigh the rig loaded rather than trusting a brochure dry weight. A weight distribution hitch and a set of air bags both restore ride height and control, and neither one raises a single rating. Trailer brakes are required by state law above a threshold that varies by state, and a breakaway battery that has quietly gone flat is the normal condition of most trailers on the road.