Trailer sways or fishtails at speed

A trailer that sways or fishtails at speed usually has too little weight on the tongue. Dexter says about 10 percent of the trailer’s total weight on the hitch, 15 percent for light trailers; Featherlite says 10 to 15 percent on bumper pulls and 20 to 25 percent on goosenecks. If the loading is right, the cause is mechanical: tires, bearings, springs or a bent axle, with typical repairs from $12 to $25 per tire mounting to $400 to $1,800 per axle installed.

Check this first

1. Check the load. Is the heavy part of the load ahead of the axles? Featherlite says heavier items go over the axles and close to the floor, with even side-to-side weight. On a horse trailer, which way are the horses facing and where are they standing?
2. Look at the hitch. Does the trailer sit nose-up behind the truck? A nose-up trailer has less tongue weight.
3. Check tire pressure on every tire, cold.
4. Match the tires. Same size and load range on every position, ST tires only.
5. Spin and rock the wheels with the trailer jacked. Play or roughness means bearings. See hub hot or wheel noise.

What is usually wrong

Full ranges are on the pricing page.

If it sways while you are driving

4-Star’s manual gives the response: take your foot off the accelerator, steer as little as possible to stay on the road using small corrections, and do not try to steer out of the sway or use the tow vehicle brakes to correct it. Once you are slowed and stopped, find out why before you go on.

Why it matters

A swaying trailer with horses in it is the worst case on any road, and on I-75 or US 27 at highway speed it is a serious one. When the cause is loading, it is the cheapest problem on this site to fix.

When to call

If the load is right and it still sways, the trailer needs a running gear check: bearings, tires, springs and axle alignment. See axle and suspension repair, tires and wheels and wheel bearing service.