Porpoising when towing on Concrete Roads

We are new trailmanor owners and have a 3124 that we tow with a 2001 Chevy Silverado pick up. On our first outing, we noticed a problem towing on concrete roads. We had a good smooth ride on asphalt, but when we hit concrete roads we started porpoising. We tried speeding up, slowing down and nothing helped. We have a weight distribution hitch and we were towing with empty water tanks. We were not carrying a lot of weight in the trailer. We are wondering if anyone else has experienced this problem and how they resolved it?
Thanks,
Carl&Judy

Have you driven the same route with just the truck? And if so do you observe similar (maybe reduced) porpoising?
We have a few concrete freeways around the Portland area here and I notice the tractor trailer rigs (apparently empty) having a slight "gallop" to them. I think it has to do with the roadway being poured in slabs as opposed to a continuous run like asphault. When driving these freeways, I notice a slight rhythmic "gallop" and the frequency does change with speed.
Just a thought but because of the WDH you have effectively lengthened your vehicle wheelbase which might amplify the effect.

As we went through N. Carolina two weeks ago we hit a long area with the woop te dos.

We also have a WDH and never encountered it before.

Just some bad roads out there!

[Bill]

We had a thread on this topic a year or so ago, but I can't find it at the moment. I'm not sure we reached any useful conclusions. Like others, I have experienced what I describe as "pounding" on these concrete roads. It is intensely annoying, but it never threatened to take control of the vehicle. In your case, does it feel like you might lose control if you had to make a quick maneuver? Or like the front end is threatening to bounce up off the pavement?

By any chance do you have anything heavy stashed way back in the trailer? Like a bike rack on the rear bumper? That can amplify the effect. And have you adjusted your WDH using the procedure outlined in the Tech Library (TM Info You Won't Find Anywhere Else)? If you weren't using a WDH, the unweighting of the vehicle's front end can make it more susceptible to porpoising. A WDH that is adjusted much too lightly would produce some of the same feeling.

There is one possibility that I have found. The tires in your truck are probably inflated to the pressure listed on the label on the driver's door. This is a "comfort" setting, intended by the mfr to produce a soft comfy ride without costing too much in the way of mpg. Next time you are going out, take a look at the sidewall of the truck's tires, and find the Max Allowable Pressure. Inflate the tires to a couple psi below this. The stiffer tires may make the ride better. In my Explorer, I think I increase the pressure from 35 psi (comfort) to 40-42 psi (Max is 44). I hope that Bobby (wmtire) will chime in on this particular thought.

But when you hit one of these concrete slab roads, I don't think anything is going to entirely eliminate the pounding.

Bill

[ShrimpBurrito]

I just experienced this effect this weekend on I-405 just north of LA, and on parts of US 101. Very painful. No significant weight in the back of the TM...empty gray tank, no bike rack, but there are 2 batteries back there. At first, I was wondering if it is waterboarding, an effect commonly found on dirt roads and created by the unavoidable up and down oscillation of vehicles. But since concrete is harder than asphalt, and since the effect is not on asphalt, I don't think it's it.

Upon closer inspection of the road at slower speeds, it seems the concrete is poured in sections, so perhaps the low spots are either in the middle of the section or at the joints.

Dave

[wbmiller3]

I-10 east of Houston is notorious for this, or has been. Ongoing roadwork seems to be helping...at the usual road-work-delays price.

Many thanks to all who responded to our question regarding porpoising. Since the last trip, we added a full height topper to the back of our pick-up truck and recently made the same trip again. Voila! The topper greatly diminished the porpoising problem. The extra weight on the back of the truck really helped. (I attached a photo, I hope it comes through)

[Wavery]

It's funny that this came up.

I recently added a WDH to my rig. The one negative effect that I noticed was that we now have that same effect on roads that we have traveled before.

I'm just wondering why you need to use a WDH on your Silverado. I wouldn't think that it would be necessary. I installed it on my S-10 because I was concerned about the lack of weight on my front wheels during braking.

I never experienced the porpoising effect without the WDH. I guess that it's a trade-off for me. I'm glad that you found a solution. My truck may be too light for the WDH....I don't know. Although, I do feel safer with it.

[Philip]

Hello Carl & Judy,

I will have to preface my comments with the fact that I have very little experience with towing as I just purchased a new 2008 2720 TM(leftover). However, I gather that I experienced the same sensation while towing as you did while towing my TM back to where I live from where I purchased her(400 miles).

My TV is a 2005 Toyota 4Runner with a Eaz-Lift Ultra(1200lb. trunnion bars) WDH. The fellow at the RV dealer where I purchased the TM installed the WDH, that I had shipped to him, while I watched. He was a bit hasty during installation and I wondered if he had taken the proper steps to set the correct tension in the WDH. Once I started on the road home I felt as if the TM pushing the rear of my Toyota up and down a bit or else the TM was pushing the Toyota forward and holding back in a slight pulsing motion. It was difficult for me to judge what exactly was happening but I didn't like the feeling. The feeling was much more pronounced on concrete roads as opposed to asphalt. Changing speed did not seem to affect the motion much at all. After driving for a couple hours I kind of came to the conclusion that the motion was more related to the rear of my TV pulsing up and down slightly. This conclusion may have been reached only because I could not conceive as to how the TM could push forward and hold back in a pulsing motion when I did NOT have the brakes applied at all.

Thinking as I drove, I remembered that the WDH manufacturer stated that you want to be careful when setting the hitch up initially not to have the bars too tight as this will take too much tongue weight off the ball and result in erratic towing. I decided that at my first stop I would loosen the chains on the WDH one link and see what happens. After doing this the TM towed much better and I had virtually none of the pulsing I was experiencing before. After loosening the chain one link I could not detect that the TV was any less level than before. I suspect the WDH was too tight. I plan to let another link out in the future to see how towing feels with yet less tension on the bars. I will also be more precise at judging how level the TV remains as I change bar tensions.

I am not sure that what I experienced was the same as your "porpoising" but I have at least found a solution to my problem.

I hope this long winded reply helps.

Take care,

Phil

[Wavery]

I recently bought a new truck (2006 Silverado 157" WB) and moved my WDH from my S10 (127" WB). All of the porpoising is gone. The truck rides smoother with the trailer hooked up then it does without it.

I think that the longer wheel based vehicles accept the WDH better than shorter WB vehicles.