Hey guys...

I have a 18' Corn Pro Flat bed equipment trailer rated at 14,000 lbs. Its a bumper pull. It has 2 - 7000 lbs Dexter torsion axles.

The trailer pulls fine when loaded and unloaded below 50 mph. However when i pull it at around 65 mph unloaded it starts vibrating the truck like crazy! Its really annoying. I was wondering if any of you have had a similar situation. The tires have been balanced by the way. I wonder if the thing needs shocks added to it. Its like it reaches a natural frequency or something at 65mph.

Any help would be apperciated. Thank you!

 

Tire seperating will cause vibration, bent rim? How do all the bolts look on the suspension, tight? Tires on the truck will cause same problem.

 

drop air pressure down to 50 when unloaded and air back up to 80 when loaded. just like you said 50 psi feels like shocks 80 feels like no shocks.

 

I am gonna make a guess and say that you may have some drive-train issues that the extra stress of the trailer makes show up.

 

I pull a 10,000 lb pequea skid steer trailer with a 20' deck, bumper pull also. Empty, at low speeds, like below 30-35mph, it will shake the hell out of the truck. It smooths right out at highway speeds, and rides back there like a tail. Also, I noticed when loaded, if I don't have the tongue weight quite right, it will start to vibrate like you said at 55 to 60 mph, and smooth out again at 65. I haven't worried about it much, like they said maybe just check all your hardware and suspension. Try changing your hitch height a little also.

 

My empty flat deck does the same thing. I've always hated it, but for some reason never spent much time looking into it... I do know my wheels are true, the tires/wheels are balanced, all bearings are good and properly torqued, and all of the suspension components are tight with new spring bushings (I just re-did all of that last spring). But, it still does it... I think it probably has something to do with tongue weight and overall attitude/angle without a load on it? I'm working on a design for a front-mounted tire carrier/cargo box/winch mount that should a couple hundred pounds to the tongue area all the time, so that will hopefully calm things down a bit...

 

TIRES the only thing back there turning!

 

I had the same problem when I bought my 16,000 gvw gooseneck flat bed.
I found the tires had flat spots on them. Replaced 3 of 4 tires. Trailer runs nice and smooth now.
I figured the previous owner had his brake controller turned up too high and was skidding the tires when the trailer was empty.

 

Thanks for the info guys! At least I am not the only one that has problems! Missery loves company ya know.

Like I said...no vibes when loaded. I pull about 8000 lbs and runs like a top! So the truck has no issues. I think the trailer starts bouncing at higher speeds. The first thing I will try is reducing air pressure. Like someone said...having 80 psi in 4 trailer tires is like running without shocks! I will drop tires down to 45 psi and see what happens. Also I do think tongue weight is an issue. I'm going to measure the weight and see what it is... Also i wanna take off the front 2 tires and see how it tows. I think the tandem tires could be hoping back and forth. This happens on big rigs too....

Thanks for the advice!

 

I would hesitate to air down trailer tires.

If you load it, they will overheat and fail dramatically.

Always MAX PSI in trailer tires.

 

I've heard that if you smoke your trailer tires even once, it can almost ruin them from the flat spots. Is this true? It's almost unavoidable with an empty trailer, it will happen a few times no matter what. I smoked em up good on the baltimore beltway when everyone decided to just stop in the road. Several smaller occasions when I just forgot to turn down the controller.

 

At 65mph it starts this problem...hmmm... I would try 75 mph and see how that works. Sometimes you just have to find that sweet spot for pulling.

 

It's the tires- your empty/loaded scenario tells the tale.

Balanced tires will run bad, especially empty, because of being out of round or because of having flat spots on them from braking/sliding.

I had an open single axle utility trailer (no brakes) that would bounce all over the place empty. Swapped the spare out for each road tire until the bouncing went away.
Took that bad tire to get balanced, and it was out of round by 3/4 in.!
Chinese junk tires...

 

my neighbor has some triple axle boat trailers, when he is pulling empty he pulls off the front and rear tires on each side and just ties them to the trailer. he said it is well worth the effort. the ride is very smooth when the springs can do some work

 

I have had two trailers in the past that have done this. Yes lowering the air pressure will help, just like a aired up basketball bounces better than a low aired basketball, same effect with your tires bouncing the unloaded trailer.

However, as someone said, loweing your airpressure to smooth the ride ain't the best thing to do, as it will increase tire failure, especially if you forget to air up when loaded.

I did a similar toolbox on front combo and it helped a smidgin. My 2 cents is find its sweet spot and run at that speed or deal with it. Even good straight no flat spotted balanced true tires will bounce.

Cory