What's causing porpoising???

[jscottsmith]

Currently pulling a 29 ft. Keystone bunkhouse from Michigan to Florida with an Expedition EL with factory heavy duty towing package. A couple of times we have run into some pretty severe porpoising. It doesn't really happen until 45 miles an hour and seems to improve slightly over 50mph.

We are new to trailering, so this is a first for us. The trailer has weight distribution bars on chains and a friction bar. My understanding is these are for sway and not bounce but there you have it.

Is this trailer issue? A vehicle issue? Maybe it's just the road we were on? Any thoughts as to what might be causing this?

thanks!!

 

[Fish]

Weight distribution bars with chains are for weight distribution, you still need a sway control device.

Reasons could be

Trailer not level
If you've got a weight distribution system I'd have to assume your trailer is level.

You're right on the edge of your towing capacity
I think this is likely

You also have to make sure your weight distributing hitch is adjusted correctly and you have your trailer loaded correctly.

Read the manual for your hitch on how to adjust it correctly or find a manual online if you don't have one.

 

[jscottsmith]

Thanks

Trailer is something like 7500# dry.Truck is rated for 9800# I think.

Looks level to me...

 

[gibsito]

Most (at least 60%) of the trailer's weight should be forward. Here's why:

 

[jscottsmith]

Most (at least 60%) of the trailer's weight should be forward. Here's why:

I've seen that. Great video!
I understand the concept. Not sure how much control I have over that. Honestly all that's past the axle that isn't factory is kids clothes.

I did have the thought that maybe I should fill up the freshwater tank as ballast. Pretty sure that is up forward.

 

[gibsito]

I would fill that tank up if it's forward. Also, you need to know your weights and weight ratings. I don't know the ratings of that Expedition, but just looking at the picture that trailer looks like a big load for it. There's a max weight rating for the Expedition, a gross combined weight rating (max weight for everything - Expedition, trailer, all gear, all fluids and all people), max axle rating for your Expedition's rear axle, etc. None of those ratings should be exceeded. You'd probably never get checked for it unless there was an accident, but then you could be held liable if you were overloaded. But just for the safety of everyone involved, it's a good thing to know all of these numbers and to not exceed them.

 

[jscottsmith]

Update. It seems to only happen when we hit a series of concrete patches in the road and the bounce just propagates. If we're on a good patch of road, it's smooth sailing.

 

[sanda]

Update. It seems to only happen when we hit a series of concrete patches in the road and the bounce just propagates. If we're on a good patch of road, it's smooth sailing.

Also make sure you are running LT tires on your tow rig.

 

[Porterhouse]

Currently pulling a 29 ft. Keystone bunkhouse from Michigan to Florida with an Expedition EL with factory heavy duty towing package. A couple of times we have run into some pretty severe porpoising. It doesn't really happen until 45 miles an hour and seems to improve slightly over 50mph.

We are new to trailering, so this is a first for us. The trailer has weight distribution bars on chains and a friction bar. My understanding is these are for sway and not bounce but there you have it.

Is this trailer issue? A vehicle issue? Maybe it's just the road we were on? Any thoughts as to what might be causing this?

thanks!!

Porpoising is caused by harmonic forces as the tow vehicle and trailer go over bumps and dips in the road at just the right speed. It is exasperated by the springs of the weight distribution hitch. Unlike the springs of your tow vehicle's suspension system, the WD springs are not damped by shock absorbers. There is not much you can do about it short of getting rid of the WD hitch, but that might require getting a larger tow vehicle that can better handle the trailer tongue weight.

 

[sanda]

Porpoising is caused by harmonic forces as the tow vehicle and trailer go over bumps and dips in the road at just the right speed. It is exasperated by the springs of the weight distribution hitch. Unlike the springs of your tow vehicle's suspension system, the WD springs are not damped by shock absorbers. There is not much you can do about it short of getting rid of the WD hitch, but that might require getting a larger tow vehicle that can better handle the trailer tongue weight.

I have found that changing your speed, faster or slower, will smooth out most road issues.