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Old 08-10-2011, 11:17 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.

Ken
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Old 08-10-2011, 11:22 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, 11:31 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, 12:00 PM   #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, 01:15 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.


Ken
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Old 08-10-2011, 01:24 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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