I recently traded my older, shorter, pickup in for a newer, longer, crew cab type. Love the room, the improved braking, the more versatile power, but.... now I have the porposing or rhythmic bucking that seems to be associated with long wheel based pickups traveling on cut concrete freeways. Whoa, Nelly! My DW used to sew while we were traveling. Now I facing a workers comp claim. After reading all the archives, there seems to be gains made by having adjustability to the suspension. For those hauling campers, that most often employs air bags. Let me get to the point. Are you having the best results in dealing with this circumstance when you can adjust the air bags on the fly with the on-board compressor arrangement? Have any of you had successful results when not carrying a camper with air shocks and compressor? It seems to me that different conditions require different adjustments and that the on-board compressor allows for this while in motion. Your insights, please.
You will probably find that most will recommend upgrading your shocks if you havent done so. I have air bags but dont use them. I do have Bilstein HD shocks and Supersprings. Porposing has never been a problem, and I carry a very heavy TC on a long bed truck.
2009 Chevy Silverado 3500 dually D/A, Supersprings, Stable Loads, Bilstein Shocks, Hellwig Sway Bar, Front Timbrens.
2010 Arctic Fox 1140 DB, 220 watts solar, custom 4 in 1 "U" shaped dinette/couch, 59 interior and exterior mods to date and still adding
I'm not sure how "harmonic oscillations" come into play, but I would first suggest new shocks as "kerry4951" suggested to dampen the up-and-down movement. Air bags are not going to do it. They are great for leveling when loaded, but are not intended nor designed to dampen or smooth out the ride. And as "Bigfootchevy" suggested, "Torklift Stableloads" will greatly enhance the overall ride, including side sway. As you can see by my sig (don't even try "weight police") that I also carry a heavy camper, but in a short box Chevy. I love my setup, and after three years, everything still makes me smile. Did I forget to mention that I live in the "Rockies", and spend most of my camping off of the pavement?
Cap'n Bob
1996 Chevy K1500 4X4 Short Box, 5.7L Vortec, E rated tires, Lance Model 820 with Cabover Struts, Firestone Ride-Rite Air Bags, KYB MonoMax Shocks, Torklift Stable Loads, Happijac Truck Camper Tiedowns and Turnbuckles, Honda Eu2000i Inverter/Generator.
The porpoising you are describing is due to frame flex of the long wheelbase frame. Like the poster above me said, he uses struts between the overcab of the camper and the truck cab's a-pillars to help dampen the flexing motion. Lance designs their campers to be used with their struts. Other manufacturers may not recommend struts be used with their campers, due to overstressing the overcab section of the camper structure.
The common solution to the bucking/porpoising on concrete freeways is either change lanes, or adjust your speed up or down until you find a speed that reduces the oscillation. Other solutions would be to recenter the load on the truck (move it back over the rear axle), or stiffen up the frame so it doesn't flex so much when loaded heavily with the load centered ahead of the axle.
I can't confirm or denie whether this is frame flexing or not,
but I can say that my 2004 Chev 1500 4x4 ex cab, 8 ft box does it terrible UNLOADED, yes, completely empty box. On a bad road I've had to slow down to under 50 just to keep the truck on the road, while all the rest of the traffic is cruising along at 65 plus.
Replacing the shocks with new Bilstein's only helped a little.
I don't know if other similar trucks have the same problem of if mine has something wrong.
Dan L wrote: I can't confirm or denie whether this is frame flexing or not,
but I can say that my 2004 Chev 1500 4x4 ex cab, 8 ft box does it terrible UNLOADED, yes, completely empty box. On a bad road I've had to slow down to under 50 just to keep the truck on the road, while all the rest of the traffic is cruising along at 65 plus.
Replacing the shocks with new Bilstein's only helped a little.
I don't know if other similar trucks have the same problem of if mine has something wrong.
BTW, going to LR D tires didn't help much either.
Dan
If it's doing it when unloaded but not doing it when loaded, your problem likely is not frame flex. The frame would be flexing more when loaded than not loaded.
Your problem is likely too much air the rear tires when unloaded. Drop them down to about 40 psi and see if that helps. Don't forget to air them back up to max psi when you load up.
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