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-   -   Porpoising (http://www.airforums.com/forums/f238/porpoising-180218.html)

WhereStream 04-14-2018 09:17 AM

Porpoising
 
A friend of mine just bought a new trailer, (an SOB, alas). He's been trying it out with shorter trips of just a few hundred miles before he points the rig West for a weeks-long adventure.

He's asking me about "porpoising," which he's having trouble with, even though he has a high-quality (per comments here) W-D hitch.

Now, I've never had this problem, but he says it is disconcerting and is ruining the experience.

The W-D hitch was installed by the trailer dealer.

Now he wants to know what he can do.

Any recommendations?

azflycaster 04-14-2018 09:40 AM

Lots of things can cause this. I would focus on the hitch setup. Making sure the WD bars are setup correctly would be something to check. Low tension on the bars can cause this to happen.

matthewsx 04-14-2018 09:49 AM

Not knowing what his tow vehicle is I would say SLOW DOWN....

Many people when they first start towing assume they can go the same speed as they did without the trailer. Unfortunately they will see others towing way faster then is safe so they figure they can do the same. Kinda like the guy who passes you in the fog, maybe he'll be able to stop in time, maybe not.

Experience is the best teacher here, lets just hope it doesn't involve a collision.

john

Adventure.AS 04-14-2018 09:56 AM

The angle of the hitch head, on some brands, is adjustable with the use of washers. A skilled hitch installer can fine tune this along with the correct size WD bars and chain tension. This is a skill that is acquired through training and experience.

YippieKiYa 04-14-2018 10:17 AM

Agreed, the WD is likely off, which might have the front end too light.

For the sake of detail, what year and make of TV are we talking about? What type of hitch? An older TV might just need shocks. Itís more likely the WD set-up, but bad shocks can cause some excess movement.

nvestysly 04-14-2018 10:40 AM

As others have said... check the weight distribution setup. Many dealers do not take time to install the hitch head at the correct angle and therefore the WD bars are actually doing very little and may be exacerbating the issue.

There are several threads about setting up WD hitches. Some of the details vary based on brand but the overall idea - to transfer weight back to the tow vehicle - is the same so basic principles apply to all.

One of the responses above mention shocks on the tow vehicle. That's certainly an item to check and it may be worth upgrading to heavy duty Bilstein's or something similar.

Also check the load distribution in the trailer. Weight centered over the axles is good. Weight on the front or back of the trailer may be contributing to the problem.

n2916s 04-14-2018 11:51 AM

So, if it is happening only when he is traveling across segmented concrete, then it is pretty common. If it is happening all the time, see above.

There are places, for example the Atchafalaya Viaduct, where the gaps between concrete segments are perfectly placed to set up a pronounced bounce that is self reinforcing so, at a steady speed, it just keeps getting worse. The best way to deal with it is to vary your speed up and down (on my rig, between 45 and 50 or so). This thrills the drivers behind you to no end...

Asphalt, even crappy asphalt, is your friend.

WhereStream 04-14-2018 11:55 AM

My buddy has a brand-new F-150.

The SOB trailer is a 23-footer, or thereabouts.

The hitch is a Blue Ox Pro.

azflycaster 04-14-2018 12:09 PM

The sway pro puts a bunch of bend into the bars. 3 1/2 links should be visible from the bar to the ratchet when it is hooked correctly. It takes some getting used to setting the arms. I have a breaker bar with a 1" socket to make it easier than with the "tool" Blue Ox provides. Also,the bars should be rated to the trailer. My bars are 1,000 pound bars and have 3 dots on the bar to identify that.

Lumatic 04-14-2018 01:24 PM

I added a Safe Ride air hitch to my WD hitch. It cut down porposing by a whole lot. Bad shocks can also add to porposing.

WhereStream 04-14-2018 01:27 PM

Thanks. Iíll ask what bars he uses.

I donít have all the details, but if I recall correctly, he was ratcheting those bars big time, maybe only one link to go.

Does that suggest he might need heavier bars?

Dan and Liz 04-14-2018 01:29 PM

One more on trailer loading — is tongue weight adequate?

AirMiles 04-14-2018 01:48 PM

I use a Blue Ox SwayPro with 1,000# bars and found 1-1/2 links showing under the brackets is my rig's sweet spot. (11th link from the loose end of the chain in the slot). I had an uncomfortable bow push from passing big rigs and occasional porpoising on concrete highways before cranking the bars to the 11th link. Here is a picture of my rig set at the 11th link with three-pass scale tickets, plus a fourth pass showing 10 links (2-1/2 links showing) for comparison. http://www.airforums.com/forums/f42/...ml#post1985301 . I do have to extend my tongue jack really high to get the 11th link into the slot.

I would start by tightening the chains/bars one link at a time, re-leveling the trailer, test driving to a weight scale and re-weighing until you find the rigs sweet spot. A dealer can't dial in your WDH unless they weigh exactly the same as you, has your family (and dog) in the vehicle, loads the rig exactly like you do for camping, and spends all day repeating the above process of up and down a link until the sweet spot is found. I doubt many dealers will do this. Most dealers will do what mine did, set my hitch to 3-1/2 links showing, leveled the trailer and send me on my way porpoising down the highway with a white-knuckled bow push. I had to spend many days learning to dial in my hitch over multiple trips to find my sweet spot. And my sweet spot changed as I made changes to the loads in my rig. But I learned how to adjust my Blue Ox SwayPro and now have complete confidence in my rigs handling. Learning to adjust your WDH is similar to learning how to ride a bicycle, you don't do it perfectly on your first try.

daveswenson 04-14-2018 06:01 PM

Quote:

Originally Posted by Dan and Liz (Post 2089213)
One more on trailer loading ó is tongue weight adequate?

I'm with Dan and Liz. How is the trailer loaded?

PKI 04-14-2018 06:20 PM

The BOSP is prone to the porpoise movement, because the bars flex. Tuning is key. Spend time at the CAT scale to get the weight distribution spot on. The trailer loadout needs to be close and balancing a bit as you scale should help dial it in.

Get as much weight out of the back of the trailer as possible. Keep the weight low and over the axles. Run about 12% of gross on the tongue. Depending on the weight bars in use, some adjustment may be required. My thought would be to stiffen them up with next size, but that would be the last thing I would consider. If not running the 1000s, give it some thought. Going to 1500s which is next increase, I would avoid.

Keep all the weight out of the back of the tow vehicle (behind the axle).

Good Luck with the tune. Pat

Edit: Follow up with rear tire pressure. Stiffen side walls, but do not degrade contact patch. May need to change brand/type/model.

PKI 04-14-2018 06:22 PM

The BOSP is prone to the porpoise movement, because the bars flex. Tuning is key. Spend time at the CAT scale to get the weight distribution spot on. The trailer loadout needs to be close and balancing a bit as you scale should help dial it in.

Get as much weight out of the back of the trailer as possible. Keep the weight low and over the axles. Run about 12% of gross on the tongue. Depending on the weight bars in use, some adjustment may be required. My thought would be to stiffen them up with next size, but that would be the last thing I would consider. If not running the 1000s, give it some thought. Going to 1500s which is next increase, I would avoid.

Keep all the weight out of the back of the tow vehicle (behind the axle).

Good Luck with the tune. Pat

See post #13 - that's the ticket.

Luigi123 04-15-2018 03:47 AM

Maybe an Air Safe Class 5. May have one for sale as I m have a Pro Pride installed May 15.

ShinyPete 04-15-2018 05:09 AM

Guessing and recommending he change hitches won't help without way more info about his rig details. If I was asked for help (and I have been 4xs with local friends)......I would......

Set RV tire pressures to max sidewall, and set TV tire pressures to maybe 10 lbs less than max sidewall. Measure hitch ball height on truck (unhitched), and coupler height on RV (level, unhitched). Measure fenderwell heights on truck unhitched. Change hitch ball height on truck if not close to RV coupler height unhitched. Read entire Blue Ox setup manual twice. Check placement of WD bar hangers on RV (chains need to be straight down when connected), and all details of ball mount install. Hookup, and apply enough force (fewer chain links showing below bracket) to WD bars to restore fenderwell heights to nearly the same on the front and maybe a 2-3" sag on the rear. If it can't be done, readjust hitch head and keep trying. If it still can't be done, he needs stronger WD bars.

Now, this is a very simple rundown, and there are more details that are needed. But this can all be done with hand tools on a level place (parking lot, driveway, etc. with RV wheels chocked), and you can find YouTube videos to walk you through it. I've setup my own BlueOx three times on different trailers this way, and it works (and my ProPride, but that's another thread :) ). Hope this helps..........

Countryboy59 04-15-2018 06:59 AM

Quote:

Originally Posted by matthewsx (Post 2089117)
Not knowing what his tow vehicle is I would say SLOW DOWN....

Many people when they first start towing assume they can go the same speed as they did without the trailer. Unfortunately they will see others towing way faster then is safe so they figure they can do the same. Kinda like the guy who passes you in the fog, maybe he'll be able to stop in time, maybe not.

Experience is the best teacher here, lets just hope it doesn't involve a collision.

john

Towing slower is a good idea but you should be able to do 70 or 75 without any weird handling. I did 62 all the way down south and 70-72 all the way back without an issue. You may want to slow down if you tend to swerve for things or change lanes a lot (I donít).

My F350/27í AS will porpoise on some roads that have lots of dips but I also need new shocks on the truck. Harmonic porpoising sometimes gets better if you speed up or slow down.

Profxd 04-15-2018 07:22 AM

The most common cause is too much weight forward and aft in the trailer (high yaw inertia). This causes it to teeter totter as you encounter rough roads.


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