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Old 09-10-2010, 04:05 PM   #1
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Porpoising

Happily rigged with the ProPride. No sway, tracks well, backs predictably, scale report in and everything rigged up just right.

Except.

Large sections of I-35 in Minnesota are ribbon-laid concrete that tend to become slightly wavy during the summer. Though some slight undulation is noticeable when bobtailing it, with the traylah, there is a pronounced porpoising effect, to the point where it is quite uncomfortable.

I have new Rancho shocks.

Any ideas?
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Old 09-10-2010, 04:28 PM   #2
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The first thing that comes to mind is to put more weight on the TV front axles. Maybe readjust the WD hitch?
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Old 09-10-2010, 04:30 PM   #3
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Unfortunately you just may be at that magic distance from your TV rear axle to the AS axle that matches the trough to peak frequency of the highway. Does it only occur on this highway? Feels fine elsewhere? You said, by scales your set up properly...are you sure? Does you TV have automatic level control and was it disabled when you performed your setup?
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Old 09-10-2010, 04:31 PM   #4
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...Any ideas?
sure

1. slow down when this happens
2. search here using the correct spelling.



not a lot u can do to alter axle positioning and other factors that lead to this condition...

so slow down and get past that area of road.

occasionally a lane change helps but not if frost/contraction/heat/expansion related.

does the tv experience this WITHOUT the trailer?

the sections of roadway i have experienced this also affected the tv withOUT stream...

see the posts around # 258-261 here...

http://www.airforums.com/forums/f464...ml#post876398l

or this thread and the many links inside...

http://www.airforums.com/forums/f464...nco-40014.html

cheers
2air'
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Old 09-10-2010, 05:15 PM   #5
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My cab bounces so bad on I80 across Iowa pulling my flatbed that I've got skull dents in my headliner. I had to bungee my jaw shut to stop my teeth clicking.
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Old 09-10-2010, 05:33 PM   #6
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The porpoising is a constructive resonance effect that will peak at a specific speed, and fall off at higher or lower speeds. The tv/trailer combination has a resonance at its pivot point, which is synchronizing with the input from the road.

Drop 1 mph every minute until you find a speed where the constructive and destructive resonances balance out.
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Old 09-10-2010, 05:43 PM   #7
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My cab bounces so bad on I80 across Iowa pulling my flatbed that I've got skull dents in my headliner. I had to bungee my jaw shut to stop my teeth clicking.

Splitrock, How about some pix?
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Old 09-10-2010, 06:15 PM   #8
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That stretch of I35 in your area is one of the worst I have been on . . . anywhere. As you most probably know, not good for the Airstream. I would avoid towing on it.

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Old 09-10-2010, 07:41 PM   #9
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That I35 in Minnesota is like driving on a plowed field. On our last trip I drove in the ditch. Much smoother.
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Old 09-10-2010, 09:25 PM   #10
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Wink I think its an upper midwest thing

On the recent trip to Northeast Iowa, We had a little of this on I-80 west of Des Moines, got some more on I-35 North of Des Moines, but when we got east of Waterloo on US-20 it was so bad that slowing to below 40 mph didn't even solve it. We ended up getting off the 4 lane divided US-20 and taking off cross country on the paved county roads. Thank goodness we know our way around the northeast Iowa boonies. A day later we rode US-20 to and from Waterloo in a minivan and it was jarring a bit, but certainly not a big deal when not towing something.

On the way back we took Iowa state hwy 3 until we got to I-35 and only experienced a little of it. Someone told us that most of the damage happened during the very hot weather earlier this summer.

We encountered nothing even close to it in Colorado or Nebraska.

The whole experience made me a big fan of recently laid asphalt highways.

Regards,

Ken
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Old 09-10-2010, 10:06 PM   #11
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If the road is older (rutted by traffic) it may of help to move to one side of the "ruts". Speed adjustment works, but mostly it is patience in getting to the end of it.

Sloppy posture behind the wheel makes it worse. Strive for upright positioning.
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Old 09-10-2010, 10:14 PM   #12
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Originally Posted by REDNAX View Post
If the road is older (rutted by traffic) it may of help to move to one side of the "ruts". Speed adjustment works, but mostly it is patience in getting to the end of it.

Sloppy posture behind the wheel makes it worse. Strive for upright positioning.
Unfortunately, in the cases we encountered, upward buckling of the concrete joints was the problem. What little rutting there was seemed to actually help a bit as if the ruts had take the the edges down some.

The one thing that helped a little, was driving in the inside lane. However I couldn't bring myself to do that when I was going 20 mph below the speed limit.

regards,

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Old 09-11-2010, 07:59 AM   #13
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Quote:
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My cab bounces so bad on I80 across Iowa pulling my flatbed that I've got skull dents in my headliner. I had to bungee my jaw shut to stop my teeth clicking.
Did ya see the sign that said, Tighten Braziers Ahead?
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Old 10-14-2010, 11:01 AM   #14
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There's a section of northbound I-75, that we traverse frequently. My rig 'porpoised' badly with the 1200# bars on an Equal-I-zer hitch. No more with the 1400# Hensley.
No matter how it was confirgured, the Equal's bars could never transfer enough weight back to the steer.
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Old 08-10-2011, 10:17 AM   #15
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Exclamation Its still there but worse

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Originally Posted by w7ts View Post
On the recent trip to Northeast Iowa, We had a little of this on I-80 west of Des Moines, got some more on I-35 North of Des Moines, but when we got east of Waterloo on US-20 it was so bad that slowing to below 40 mph didn't even solve it. We ended up getting off the 4 lane divided US-20 and taking off cross country on the paved county roads. Thank goodness we know our way around the northeast Iowa boonies. A day later we rode US-20 to and from Waterloo in a minivan and it was jarring a bit, but certainly not a big deal when not towing something.

On the way back we took Iowa state hwy 3 until we got to I-35 and only experienced a little of it. Someone told us that most of the damage happened during the very hot weather earlier this summer.

We encountered nothing even close to it in Colorado or Nebraska.

The whole experience made me a big fan of recently laid asphalt highways.

Regards,

Ken
An update from our recent trip to Iowa following same route as last year:

All the bad patches from last year are now worse than before. There are now some very bad places west bound on I-80 in central Nebraska. There is a long stretch of porpoising in the right lane southwest bound on I-76 in colorado. We are seriously considering not taking the airstream anywhere east of Denver.

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Old 08-10-2011, 10:22 AM   #16
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I will second that! East of Denver is bad.....it was so bad I had to stop and see if it was my wheels or tires.
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Old 08-10-2011, 10:31 AM   #17
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On bridge approaches and exits, I'll try to move off center to avoid the bone crunching, shock breaking, bump-stop trashing when we hit the connection.
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Old 08-10-2011, 11:00 AM   #18
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The porpoising is a constructive resonance effect that will peak at a specific speed, and fall off at higher or lower speeds. The tv/trailer combination has a resonance at its pivot point, which is synchronizing with the input from the road.

Drop 1 mph every minute until you find a speed where the constructive and destructive resonances balance out.
The takeaway I get from this is when looking at a tow vehicle, it isn't a half bad idea to tow test it (if possilble) on a previously identified road section which promotes porpoising. Each tow vehicle/trailer becomes a unique vehicle which is subject to these resonances, and hopefully you can shift the porpoise speed to a speed you don't drive at.

I come to this conclusion from experience towing with my 99 F250 short bed supercab. It was a bucking bronco towing on broken concrete block freeways with a clear resonance at my typical towing speed. The similar sized Tundra has no natural resonance at this speed and is a much more pleasant tow. For all I know the Tundra could kick in 10 MPH faster, but I don't drive at that speed.
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Old 08-10-2011, 12:15 PM   #19
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The takeaway I get from this is when looking at a tow vehicle, it isn't a half bad idea to tow test it (if possilble) on a previously identified road section which promotes porpoising. Each tow vehicle/trailer becomes a unique vehicle which is subject to these resonances, and hopefully you can shift the porpoise speed to a speed you don't drive at.

I come to this conclusion from experience towing with my 99 F250 short bed supercab. It was a bucking bronco towing on broken concrete block freeways with a clear resonance at my typical towing speed. The similar sized Tundra has no natural resonance at this speed and is a much more pleasant tow. For all I know the Tundra could kick in 10 MPH faster, but I don't drive at that speed.
My experience with our quad cab short bed pickup and classic 31D on the segment poured concrete highways is that once 45 MPH is reached, the bucking simply gets worse as speed increases. 65-70 is our normal towing speed and thus us we usually encounter it initially at that speed. The amusement park quality ride does not improve until we slow to below 45. The leaves a slim margin as the minimum speed limit is usually 40 or 45.

Sometimes, driving in the center lane helps, but then that can cause problems with other drivers. . On the bad part of I-76 when we first encountered it we found semis driving in the center lane. from then on we just followed suit as it was considerably smoother.


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Old 08-10-2011, 12:24 PM   #20
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There's a section of I-10 East of Houston, West bound, that causes all vehicles to porpoise. It even happens when not pulling anything. It's like the turtle back was sculpted the wrong way.

Just slow down to lessen the effects.
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