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Old 03-29-2012, 06:21 AM   #1
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Concrete roads and porpoising

I have played with my WD several times. Add links, take away links but still all that bouncing. Paved roads are just fine. But concrete roads are bad. Is it something I'm doing wrong or should I always make sure I use the men's room before I go?
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Old 03-29-2012, 06:27 AM   #2
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This is usually a sign that there's not enough weight on your lifter bars. Your bars may be too heavy or too light for your trailer, too. To get more detailed, the experts will need to know what hitch you have, what weight lifter bars you have (usually marked on them - for example mine are 1200 lb), and ideally the tongue weight of your trailer (if you know it).

I was having the same problem, but I tightened up my lifter bars and it has totally gone away.

You may also have too much weight in the back of the camper.
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Old 03-29-2012, 06:41 AM   #3
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more reading here:
porpoising - Google Search
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Old 03-29-2012, 07:02 AM   #4
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We have a section of Interstate 90 here that porpoise's our Burb whether towing or not. The frequency of the seams interacting with the wheelbase.
Slowing to 55mph is the best option to reduce the aggravation while towing.

That being said, it is very important to have the proper weight returned to the TV steering axle, with a level rig, TV & AS.

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Old 03-29-2012, 07:35 AM   #5
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I have found that there are particular roads that cause porpoising no matter how the WD is dialed in. The only things to do about it are slow down or take another road.

Stiffer rear shocks might help matters somewhat, too, did that in my pickup. It helped a little.
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Old 03-29-2012, 09:56 AM   #6
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I had that problem once on I-90 traveling east just inside of Montana. The right hand lane was so bad (at almost any speed) that it was getting uncomfortable to ride in the car. The left hand lane was perfectly fine. There was little to no traffic. Any guesses as to where I was driving? ;-)

Anywho, I don't think that it had anything to do with hitching, it was just a bad stretch of road.

Are you having these issues all the time or is it only in certain areas?
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Old 03-29-2012, 10:14 AM   #7
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This is a common problem on aging concrete highways (and sadly, some newer ones). It seems that the middle of each concrete slab is depressed in relation to the edge. Once on I-35 in southern Minnesota I saw some nice grinding at the junction of each slab and that sure did ride nice! The second solution comes later in life when they give it an asphalt topcoat.

MN-23 between Ogilvie & Mora is very bad and a common route between us and Duluth/the Northshore. I do a personal detour to avoid it. About the very worst I've seen on fair-condition interstates is I-90 between Madison, WI, and Rockford, IL. I-90 between Rochester, MN, & LaCrosse, WI, has been written up but has nothing to compare the beating I get both directions on the Madison-Rockford section!

http://www.airforums.com/forums/f42/...oad-34017.html
http://www.airforums.com/forums/f464...nco-40014.html
http://www.airforums.com/forums/f464...mph-61233.html

These are real rivet breakers! When I find myself on one I've had to just get in the right lane and go as slow as 35-45 mph and just get through it. Detours are hard to come by when you're on a 4-lane...
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Old 03-29-2012, 10:32 AM   #8
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"porpoising" seems like such a graceful description for what I've experienced...

maybe we should call it emesising

Dolphins Porpoising - YouTube
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Old 03-29-2012, 10:35 AM   #9
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Question

"Any guesses as to where I was driving? ;-)"
Butte...

Bob
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Old 03-29-2012, 11:56 AM   #10
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I think there's some combination of wheelbase, spring rates, and who knows what else that causes porpoising in some trailer/tow vehicles on certain stretches of concrete highway.

My 1999 F250 super cab and Airtream would porpoise between about 50 and 60 mph. I tried to run it at 62 which is right on the edge of a ticket here in CA, to avoid porpoising. It was not always possible to go that speed due to traffic. I tried hitch adjustments, shocks (Bilstein) but nothing seemed to change the fundamental porpoising.

I replaced the truck with a Tundra, nearly the same wheelbase, and it doesn't porpoise in that speed range. Perhaps it porpoises in a different speed range, but it isn't one I drive in. For me it was a huge relief the first time I towed with the new truck.

The porpoising is surely uncomfortable, and at its worst for me it bordered on dangerous or damaging. If there's some way you can tow test a new tow vehicle (when in market), I'd surely recommend it over rough concrete. Probably every rig has its harmonic frequency and you don't want it to be at speeds you drive.
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Old 03-29-2012, 12:42 PM   #11
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The airsafe hitch really helps with that condition.. atleast it made a huge difference in my case.

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Old 03-29-2012, 12:49 PM   #12
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Don't know what Tiger tows with, but like tpi, in my experience I have found that a 3/4 ton is much more likely to porpoise, towing or not towing than a 1/2 ton. In that case it would seem that the "stiffer" less "forgiving" suspension is part of the problem. This happens to me quite often on the westbound span of the Chesapeake Bay Bridge. The concrete sections all have pretty good bumps as you move from one to the other. I just slow down and it pretty much goes away. For example: last weekend coming back from Assateague the wind was gusting to about 40 mph, so I drove much slower than usual over that rather high (186ft above sea level) bridge and didn't experience nearly as much porpoising as I do at my normal speed. We don't have a lot of concrete roads around here, but I know on the newer concrete Rt 50 Salisbury, MD bypass, it rides nice and smooth, same on the newer Rt 50 bridge at Cambridge, MD.
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Old 03-29-2012, 01:35 PM   #13
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Small World!

Quote:
Originally Posted by ROBERT CROSS View Post
"Any guesses as to where I was driving? ;-)"
Butte...

Bob
Ha! Sounds like we were "enjoying" the same stretch of road. If I remember correctly, they were in the process of repaving the pass. Maybe there's hope that they'll keep going and fix that section.
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Old 03-29-2012, 01:47 PM   #14
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Put some heavy duty shocks on the back of your tow vehicle. The purpose of a shock is to damp out periodic motions. The load bars only add spring rate and don't add damping. I believe Airsafe hitches provide some damping. Too little weight distribution can contribute to this. A little porpoising is probably not a bad thing. If the system is too rigid you are transfering a lot of stress to the frame of your tailer and tow vehicle.

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