Fifth Wheel Fishtailing

Bring us specifics. We can help. What tires...Manufacturer name, Size, load range, air pressures. With out that info we cannot help you.

Recently replaced all tires, truck & trailer, and have noticed a slight fishtail effect at higher speeds 55-65 MPH.

The 'type' of tread is what causes tire roll on any heavy vehicle.

Too aggressive of a tread, and the outer one flexes. Take two fingers and see if you can move the tread back and forth easily on the outer tread of your 'new' tires. If you can there's your problem.

Amazing what just a small amount of flex can do even on the non steering FW. Henceforth why semi front tires have a bald flat slick for an outer tread.

Been there done that.

I screwed up a perfectly handling MH when I put too aggressive tread Mich's on it.:(

Tire pressures are always the first suspect. The second suspect would be whether the tires now mounted are rated to carry the loads you have in the first place. That is, did one or more lower-rated tires sneak into the mix, compared to what was there before?

rozapaul, I had this early this year when I put new tires on my truck.. GOSh it was awful to drive, Worried me to death that I had screwed up front end. Took back to tire guy and he lowered the pressure down to 75psi per tire on the back and 70psi on the front. Told me I was good to go! really??? you know what he was right once I drove this set up the truck felt a lot better and handled like I was used to it. He told me the new tire depth allowed the tire to ride and flex on the thread tops making it squirrely feeling.. This past trip I pulled 200 miles one handed on the wheel until i got around others vehicles.The guy sells me all my tires and has for 20 years.. straight shooter when it comes to tires front end work, brakes and shocks, etc.
JMHO
randy

I had tread roll with the last truck I purchased... after several towing trips and the truck was broke in.. It all went away and was smooth,,,

What is your pin weight percentage?

Same type of tires on truck and/or trailer....or different thread/sizes this time?

Air pressures...same as prior set up?

I don't notice any changes with new trailer tires but do go thru a 'period' that is different with new truck tires....even same brand/type of tires

What load rating did you get?Side wall roll due to under inflation or low load rating,ST's on RV? Same as original that apparently were no problem?

9 makes a good point on tire break in. You can have too much or too little air pressure.
I would add if you placed a AT (all terrain) tire on the truck with the larger lugs and voids it can exhibit tread roll which is like driving with half flat tires. They also will get better with miles.

Same with the trailer.
And bias ply tires on a trailer with radials on the truck may cause sway issues.

Check all air pressures and also new tires will feel a little sloppier than old ones. They will need to break in and you will need to get use to them.

Does it feel like you are out of control or does it just feel like the truck is a little less responsive?