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Old 03-29-2012, 02:11 PM   #15
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With single axle and tandem axle Airstreams in past few years, we had same bouncing on the same stretches of road. I don't think its good for the truck, trailer, or us. We either slow down or if still rough, detour around it.

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Old 03-29-2012, 04:55 PM   #16
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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.
My 2011 F350 SRW does fine over those bridges when towing the 30' Classic - maybe some of the newer Super Duties and/or 2500 or above trucks have a bit better suspensions? :-)
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Old 03-29-2012, 05:17 PM   #17
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Concrete roads and porpoising

Porpoising was a constant problem with only one of my tow vehicles, and that was my 1995 K1500 Z71 Chevrolet Club Cab Pickup. The most objectionable stretch of highway was US 151 from DuBuque, Iowa to Madison, WI - - then I-90/I-39 into Rockford, IL from Madison, WI - - speed made no difference nor did hitch adjustment -- softer rated shocks did help some as did derated rear springs on the truck but it was never completely remedied. All I had to do was switch to a different tow vehicle -- the problem disappeared when I switched to my 1984 Jeep Grand Wagoneer, my 1975 Cadillac Eldorado Convertible, my 1965 Dodge Coronet 500 Convertible, or the problem disappeared when I traded the pickup on a new 1999 K2500 Suburban in April 1998. My conclusion was that it had something to do with the harmonics created by the distance between the tow vehicle axle and the trailer axles ('64 Overlander) in the pickup that was not replicated in any of my other combinations -- all being towed over the same stretch of highway.

Kevin

P.S.: I have had no problems with the Suburban and either of my coaches porpoising anywhere that I have traveled from the Blue Ridge Parkway and points to the West. The pickup, on the other hand, proved problematic with either coach on nearly any route having concrete surfaces with prominent expansion joints - - porpoising would be immediate and remain a constant until a smooth strech of asphalt was encountered.
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Old 03-30-2012, 08:02 AM   #18
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It has to do with the space between the axles of the TV and the coach. The slabs of concrete on the highway have been shifted by the heavily loaded semi trucks. This is why the right lane is always worse.
It happens even when you are not towing the trailer when the axle spacing on the TV is the right length.
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Old 03-30-2012, 08:19 AM   #19
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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.
Even though it was over 10yrs ago with our 63 that Butte-ful section of road still stands alone, sounds like not much has been done since.

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Old 03-30-2012, 08:58 AM   #20
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steel road plates

“porpoising” was the December night three years ago we were towing westbound across the downhill side of the Tappan Zee Bridge and suddenly found the outside lane, without any real warning, fully populated with the dreaded “steel construction plates”. I was pulling the 31’ 1976 Sovereign at about 40 mph.

I was on the brakes immediately, but not before we already “rolling” over the second one. those plates felt like they had to be 3 or 4 inches tall....

for more than just a brief moment, I thought the trailer was coming over my shoulder!!!

thankfully, it stayed behind the truck….
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Old 03-30-2012, 09:24 AM   #21
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It happens even when you are not towing the trailer when the axle spacing on the TV is the right length.
True, same problem with our VW camper Eurovan (new Bilstein shocks installed) on certain stretches of road.

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Old 03-30-2012, 09:36 AM   #22
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I added air lifts to our F250 to help keep things level when carrying a lot of stuff and towing; this has allowed me to largely tune that out of the suspension. I carry about 20 lbs of air when towing, and things are much better. The longer trucks are less subject to this I think.

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Old 03-30-2012, 10:50 AM   #23
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'Years ago' before considering towing an Airstream we towed a 2000 lb popup with the same car. This problem here and other issues almost discouraged me from moving up to the Airstream. Never heard of WDH. I quickly discovered that no amount of air pressure in the rear air shocks would lower the front of our Buick. My neighbour came to our rescue by GIVING us his old WDH setup that was in his shed for years. It is a 1000 lb bar setup which sounds like too much but is perfect. Towing our Airstream is SO much better than the popup.
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Old 03-30-2012, 12:02 PM   #24
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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.

Probably every rig has its harmonic frequency and you don't want it to be at speeds you drive.
Yes. Lots of factors go into this and what works everywhere else may not work on a specific section of road with the expansion joints at just the perfect distance to resonate with your rig. A perfect set up will not be perfect for every road and somewhere out there is a road waiting for you to rattle your teeth.

We noticed it in S. Cal., a place where it is often reported whether towing or not. There is a section of I-70 east of Denver near Limon where it is very bad. We haven't noticed it many other places, but when it happens, it is almost always on a concrete roadway. Long before we had a trailer, it would happen sometimes on some concrete roads regardless of what vehicle we were driving.

This can also happen on a gravel road when it has a lot of washboard. Same principle. Sometimes going faster helps, sometimes slower, sometimes nothing helps. Putting the tow vehicle in 4WD on gravel can improve stability on gravel. We try to find a speed that doesn't resonate with the road surface and hope the overhead cabinets aren't on the floor by the time we finish that stretch of road.

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Old 03-30-2012, 01:06 PM   #25
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The porpoising is surely uncomfortable
Especially for well-endowed women. I was giving one of my women friends a ride once and hit a bad stretch and she must have felt terrible. Wasn't anything I could do about it though.
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Old 03-30-2012, 01:18 PM   #26
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Especially for well-endowed women. I was giving one of my women friends a ride once and hit a bad stretch and she must have felt terrible. Wasn't anything I could do about it though.
Not without letting go of the wheel anyway....

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Old 03-30-2012, 11:05 PM   #27
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Old 03-31-2012, 01:11 AM   #28
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Especially for well-endowed women. I was giving one of my women friends a ride once and hit a bad stretch and she must have felt terrible. Wasn't anything I could do about it though.
Good to keep an eye on things just in case of trouble, though.

- Bart
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