Trucks & Trailers - Trailer Bouncing during Towing

Hello All!

Back before the new year I decided to replace everything on my 1993 bass boat (single axle) trailer -- springs, u-bolts, wheels, tires, hubs, and bearings/races...everything except the original axle.
I haven't towed the trailer more than 20 miles since doing all this, and most of those miles were with the boat off the trailer. But anyway, I was taking the boat over to the marine shop, less than half a mile away from where I keep it, for maintenance, and until I got up to about 20-25mph, the trailer seemed to bounce up and down slightly, like I was driving over a row of small speed bumps. It wasn't so bad that it seemed dangerous, but I could definetly feel the up and down motion while pulling it with my Dodge 1500. It stopped when I got over a certain speed and then pulled just fine. I also remember it doing this also when I first took it back home after replacing everything, with the boat off the trailer.
Any suggestions to what could be causing this? Is everything just 'breaking in'?
Thanks for any input! JBT

Did you have the wheels/tires balanced? My experience is that many trailer wheel/tire combinations require a lot of weight to get them to balance.

No, I sure didn't. You think that is the solution?

I'd give it a try. My current set of tires didn't require too much weight, but when I had the last set balanced the tire shop guy told me I was wasting my money; when I went back to pick them up he was recommending which tires I should use as spares based the amount of weight needed to balance them.

Ok then, I may get that done. Shouldn't cost too much anyway...worth a try. Thanks!

I have been told bias ply tires get out of round when they set for a while, when you pull the trailer the tire become round again after a short distance.
John

I have been told bias ply tires get out of round when they set for a while, when you pull the trailer the tire become round again after a short distance.
John

This is true, but it's not the OP's problem because he said that the bouncing stopped after he reached a certain speed. Need to balance your tires.

Natural resonant frequency. The easiest way to change this natural frequency is raise/lower the tire pressure. Mass is next. Notice it doesn't bounce with the boat on it? Natural frequency changes.

I have this happen before with boat trailers, and my current utility trailer does it when unloaded. I've never worried about it on boat trailers since they are rarely towed unloaded. On my utility trailer, if I have to tow it any distance unloaded, I just put my 5 gallon water jug (filled) near the front, which stops the bouncing.

Under inflated tires could cause it to bounce when loaded. I'm not sure about an empty trailer bouncing.

Thanks guys, I appreciate it...I'll get the air gauge on them but they should be still right around the recommended pressure rating, but I'll double check. Thanks again!