Why does my trailer fishtail?

To the horror of many, I pull trailers with tongue weights all over the place. No problem in and of itself. All by itself, tongue weight has no effect on sway.

Trailer sway comes about from motion. Most folks can't figure that out for some reason. Lets start at the back and work forward.

1. If the trailer wiggles side to side over the tire contact patch, it's going to sway. This is typically caused by weak tire sidewalls, low tire pressure, loose wheel bearings, and sloppy trailer suspension.

2. Cheap trailers tend to have long flimsy tongues. You can get a lot of nice sway going with this, especially if you load them nose heavy. The longer and flimsier the tongue, the more the trailer sways as it turns from side to side.

3. A sloppy hitch lets the nose of the trailer turn side to side. It's not common with car trailers, but if you ever pull with a pintle hook, you'll certainly learn about it.

4. A poor hitch on the tow vehicle. Many of them are really poorly built, particularly the universal hitches and the lightweight category I-II hitches. They let the hitch ball move side to side, turning the trailer nose from side to side, so it sways back and forth going down the road.

5. The tow vehicle tires. Front and rear. Most tow vehicles have *lousy* towing tires. With the nice squishy sidewalls, the tow vehicle sways side to side, swinging the hitch ball side to side, turning the trailer nose from side to side, so it sways back and forth going down the road. I watch this one all the time. Foolishly, many people ignore the front tires of the tow vehicle. They come into play for stability almost every bit as much as the rears.

6. Trailer loading. It's usually not a factor. But overall, centering the weight of the load over the axle will create the least leverage on the trailer, and keep the induction of sway to a minimum. I know, people swear about trailer loading. That's fine. What they are doing is masking the problem, not addressing it. Same with slowing down.

7. Trailer length. Short trailers are angularly affected by the nose far more than long trailers. As such, they are much more prone to wagging. And as such, they are much more demanding of good tires and such to prevent them from wagging.

8. Axle slightly out of alignment or bent. An axle out of alignment (dogtracking) will jerk to one side. Many people confuse it with swaying. Usually it not noticable empty and gets worse the more it's loaded. A bent axle that puts the two wheels out of alignment with eachother will sway or jerk (depends on how it is out of alignment) as it can't decide which tire to track.

__________________
If the grass looks greener it is probably over the septic tank. - troy n sarah tx

Our existance here is soley for the expoitation of CMG

8a worse yet both tires angled off to the same side.

Tongue weight has much to do with trailer sway.

I played with enough boat trailers to know that for a fact. The last boat I dragged home I drove a thousand miles to get. The owner had cut off part of the tongue and pushed the boat back on the trailer to fit it in his garage.

I could pick up the tongue with three fingers. The entire package weighed about 3000 lbs.

That particular set up would start swaying behind my F 150 at about 60 mph. At 70mph is was down right scary.

I re-rigged the trailer set up when I got home, getting it to have about 200 lbs on the tongue and it rides nice at 75 mph now.

You want your trailer set up so that there is enough weight on the tongue so the trailer has a nice "three point" stance. Not enough weight on the tongue and the tongue will want to go up and down and side to side at the will of the forces placed by the entire load on the axle.

This of course refers to tow vehicles with the hitch points aft of the axle.

Tractor trailers are completely different animals and are ruled by different rules of physics.

Dropped the ball 2" and found a hunk of steel for ballast, problem solved!