Brand New Truck Campers and Loving It! Part 2: Porpoising and Camper Stability

Kielhwl

New member
We’ve had our new Phoenix truck camper since mid June and finished an 8 day shakedown cruise through the Black Hills and Badlands of South Dakota and 3 more weekend trips around home. See our Part 1 Post at www.expeditionportal.com/forum/threads/82033-Brand-New-Truck-Campers-and-Loving-It!-Part-1-The-Pickup that described picking up the camper and falling for the simplicity and flexibility of truck camping.
On our second day of being brand new truck campers, we experienced porpoising, that sudden onset of a mild to severe fore and aft pitching of the camper. Above about 70-75mph and mainly on concrete roads, a resonance occasionally caused a rapid buildup of porpoising. Slowing down caused it to dissipate immediately. Sometimes the buffeting slip stream of a semi truck could set it off. The first time it happened, it was severe enough, that we sent an email to Rob back at Phoenix who patiently re-iterated what he told us earlier about a “truck to cab blanket” (a small inflatable inner tube to support and absorb the shaking) and the 3M Clear Bra to prevent paint damage to the roof of your truck. He reassured that porpoising was not going to cause structural damage to the cab over. Being in the middle of our shakedown cruise, we did not want to try to stop, find and install the truck to cab blanket, so we just slowed down when it happened.
We did some additional research and found very little scientifically sound information in the various forums about the causes or solutions to porpoising. Yes I believe Lance Cabover shocks will eliminate it, but they are expensive and seemed like over kill for our relatively light weight camper. Upgrading the truck’s suspension might help, but there were very mixed reviews on how effective it really is. Plus it’s expensive too. The Truck to Cab blanket seemed to work for most people, but didn’t have a lot good reviews about its durability or having to change pressure when going up and down mountains.
So I thought about this and decided to try a simple experiment that cost me $4. I bought a 3 inch diameter swimming noodle – those stiff foam floatation tubes kids use in the pool. I cut 2 sections about 8 inches long and squeezed them under the cabover near the edge of my truck top and took a high speed drive down a nearby concrete highway. It worked great, no porpoising at all. It also seemed to add a lot of overall fore/aft stability to the camper.
I had one reservation. I didn’t want to concentrate any pressure points on the cabover or the truck top, so I decided buy a large piece of foam for under the cabover to distribute the pressure. I also bought a 12 by 60 inch 3M Clear Bra to protect the paint - $30. The foam is called Drylast and is for outdoor furniture pads. It is designed to let water run right through it. It’s an open cell foam with a density of 1.8 lbs/cubic ft (measure of durability and nothing to do with stiffness - higher is better) and a 25%IDL of 60 lbs (a measure of stiffness – higher is stiffer). I’m not an engineer, so didn’t really know if it would be stiff enough so I hesitated a bit since it was fairly expensive. A 12 by 60 by 3 inch pad was $50 with shipping. Maybe it turned out to be a bit too stiff, but not much.
When I got the foam, I cut a slight “V” shaped leading edge to help shed wind (probably over thinking a non issue). I also cut a deep “V” shape on the back side and “shaved” the center down an inch to about 2 inches thick so there would be less lift in the center of my truck. I want most of the support on the sides where the truck and the cabover have more structure. I lifted the camper a couple of inches, installed the Clear Bra in about an hour, laid the foam on top of the truck with 4 self adhesive Velcro pads on the camper side (top) side to help the foam stay in place and lowered the camper back down. The foam pad is all centered over door supports/frames to minimize any forces on the top of my truck. That weekend we went on a 600 mile camping trip and had zero porpoising and significantly better overall stability of the camper in the truck bed. Unlike the Cab to Truck Blanket, I don’t have to worry about it bursting when climbing high mountains. Next time I take the camper off, I may shave another ½ inch from the center. The camper seems to set about ½ inches higher and I don’t want to add any unnecessary forces to the cab over.
Think hard about it before you try, but for my camper, this works great and only cost about $80 for a long term solution to porpoising.

P. S. Rob from Phoenix is a big believer in minimizing the step front edges on the truck minimizing wind damns to cut wind resistance and improve gas mileage. Based on a limited sample, I went from about 13.2 mpg (1300 mile sample of interstate driving) to 13.8 (600 mile sample of interstate driving) when I added the foam closing the gap between the truck top and the cab over. If you follow Rob’s logic, you want to minimize the gap between the truck top and bottom of the cab over to prevent a wind damn. The foam helps fill in the gap. In full disclosure, I also took off my Happy Jacks for this last trip which probably had a bigger effect than the foam?



tc cabover suspension.jpg
The experiment with the swimming noodle.

foam front view.jpgside view foam.jpg
side and front views with the permenent foam.
 

haven

Expedition Leader
"Above about 70-75 mph..."

I'd advise that you don't drive your loaded truck the same way you drove when unloaded. Keep your speed to 60-65. 55 is even better. You'll get much better fuel economy, and you'll be able to enjoy the scenery.

"We weighed in at 8000 lb..."

The Toyota Tundra has a GVWR around 7200 lb, depending on configuration. So you're running overloaded. Helper springs or air bags, plus heavier shocks will keep the load under control. Or trade up to a 2500 series truck.
 

Kielhwl

New member
Already did a Timbren SES upgrade. It may have helped the porpoising a bit, (it was hard to tell if there was any impact to porpoising) which I why I went and added the foam. The Timbren gave me back about 2 of the 3 1/2 inches I had my back end settle with the camper laoded. I do think I have a bit better cornering, but again, it is really hard to tell. Still glad I did the Timbren upgrade since it was cheap, easy, and did reduce about half the rear sag which will hopefully help prolong my suspension's life.

I'm not sure if I should have gone with air bags instead since they would have been "stronger". But since I was having essentially no handling issues that I could feel, I went the cheaper and no maintance route with the Timbren. As of now, I can barely tell I have a camper back there except when I go to the pump. Even at high interstate speeds I only lose 1.5 MPG.

Before the foam, at any speed, any good bump, truck passing would cause it to porpoise a bit. With the foam, I never feel anything especially the really bad ones on concrete highways, at speed (or good head winds), or with a fast truck passing.
 

redthies

Renaissance Redneck
Funny haven, I was thinking the same thing... "ABOVE 75mph". "Even at HIGH interstate speeds" too? Slow down and you won't have "porpoising" issues. I towed my various camper trailers at the posted speed, which is sometimes 70, but with a slide in truck camper in a half ton, that can be a dangerous game.
 

TCcruzn

Observer
Two things will fix the porpoising- Rancho 9000 shocks all the way around, and seeing a podiatrist about your lead foot. You may even experience another benefit- improved mpg. I have a much heavier Lance and do not have a problem with the porpoising.
 
Top