Porpoising

[Spindrift]

Don't know if "porposing" is the correct word for describing this but I'm talking about front to back rocking during towing. This situation sometimes occurs, but only on secondary roads, never on the interstate. I'm wondering if this rocking is the result of road conditions or my trailer set-up. I've measured distances from truck and trailer body to pavement and I'm level in that respect. I've weighed the entire rig but I don't know exact tongue weight. According to the rv.net police, my 34' trailer length is well beyond what is considered appropriate and safe for the truck.

[Billman]

'Porpoising' is a term that is used in the Drag Racing industry. It is when a rocking motion from front to back is happening. So as far as I can tell, you are right.

It is corrected with spring rate changes and shock adjustments.

Relate this to towing trailers and I would have to guess on adding or removing tongue weight. That doesn't mean it has nothing to do with the road conditions though.

Tire pressures may help also, but I wouldn't go too low...

[HowieE]

Porpoising in a towing setup is a result of the effects of the resonant frequencey on the complete package. Factors that go into ptoducing it are road speed, wheel base, trailer length and axel loads and repetive road falts. Porposing is most often produced by roads made from concrete slabs that have a dividing strip ever 25 feet or so. These repetive point of impact coupled with the natural resonance of the combined vehical produces porpoising.
While Jersey and Pa have a local compition going for the worst roads, Pa has won for the last 10 years or so, Route 10 in La. is the national winner by far.
If encountered while on a trip the best thing to do is slow down or change roads.
The mechanical considerations to reduce this, and I say reduce it because you can only change a resonant frequency of a mechanicl system not eliminate it, are good shocks, insure that your weight distrubiting hitch is moving weight to the front axel and trailer axels, install shocks on the trailer axels if they are not already there, checking trailer dry tongue weigth to make sure it is reasonable, 10 to 12% of trailer, and insure the tire pressures are inflated to reflect the loads on each axel set after weight distrubution.

[Billman]

Howie

Ask any Long Islander what the worst road is and they will tell you the Brooklyn-Queens Expressway--- Period . Ask anybody who has driven on it and they will agree. Commercially, it's the only way off the Island.

New York State is the winner in worst roads.

[markrinker]

Too much tongue weight. Where do you load the cargo in your trailer? Try moving anything possible rearward over or behind the axles.

Other easy remedies include adding Timbren springs for the truck, load equalizing hitch adjustments, and/or heavier rear shocks to stop oscillation.

You might be too long for most people's thoughts, but not too heavy.

[HowieE]

Billman

Sorry I did not include "Parking Lots" in my comments. There is no resonant frequency while stopped, it's just the earth moving under your feet.

[Turbine Doc]

Spin

check out www.activesuspension.com (http://www.activesuspension.com) it really helped my overall towing regardless if I'm bumper towing a utility trailer, my Bronco 2, or my GN trailer, try it they have a 30 day guarantee as well my guess though from my experience is you will keep it.

[Mudflap]

The active suspension also completely eliminates wheel hop. It is the greatest thing that ever happened to towing

[Spindrift]

I had heard about Active Suspension but I was under the impression that the system was designed more for the 1/2 ton trucks owned by "weekend warriors". These trucks usually experience more roll when loaded than their 3/4 and 1 ton big brothers.

I didn't realize you could get the springs for the HD trucks.

[Turbine Doc]

Spin they allowed my 1/2T weekend warrior to haul a 12K GN trailer load, but I installed the 3/4T set in lieu of the 1/2T set. I don't know its there unless towing.

[Spindrift]

Tim,

I hope you realize I'm not suggesting that you, or any other member of this forum is one of those!