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Old 01-11-2015, 11:19 AM   #1
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Does porpoising affect my toad?

I have a 98 Beaver Ticonderoga and a Fiat 500 toad. Virginia has a lot of bridges where the road on either end of the bridge has subsided or the road was constructed with a dip. This causes some pretty severe porpoising if I don't see the dip in advance and slow down. As a relative newbie, I have only towed the car a few times, I am concerned what the porpoising will do to the toad. I haven't seen any issues yet and I don't see any issues looking in the rear split camera I installed which looks at the hitch. Does anyone have any words of wisdom regarding any adverse effects of the porpoising on the toad?
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Old 01-11-2015, 11:33 AM   #2
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Check the attachment bolts on the base plate at least annually. Porpoising puts a lot of stress on the base plate and you want to make sure it's not working loose.
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Old 01-11-2015, 11:50 AM   #3
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The porpoising should be solved. Shocks and/or suspension issue are likely.
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Old 01-11-2015, 12:15 PM   #4
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I've had occasional severe porpoising over the years with no damage to the toad.

New shocks will help but every now and then you'll hit some real bad road....I10 near New Orleans comes to mind.
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Old 01-11-2015, 02:12 PM   #5
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Richard.....I'm thinking you may be a little overly concerned since you installed a camera. You have a very lightweight toad and it shouldn't be a big issue.

Most likely, the Fiat doesn't have a lot of structure under the front end and they probably had to use multiple attachment points to install the tow plates. For that reason, you need to just keep an eye on plates as "FlyingDriver suggested. Otherwise, relax and enjoy.
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Old 01-12-2015, 02:07 PM   #6
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Heading for an RV park in Desert Hot Springs I had a "porpoising" event. When we got into our spot I found that the Closet Rod with my cloths on it had broken free of the cheap plastic mounts. Definitely a surprise for us.
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Old 01-12-2015, 03:11 PM   #7
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As a total newbie can some one define "porpoising"?
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Old 01-12-2015, 04:04 PM   #8
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Quote:
Originally Posted by Punxsyjumper View Post
As a total newbie can some one define "porpoising"?
It's the front-to-back rising and falling motion (in the manner of a porpoise), experienced when driving through a dip in the road.
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Old 01-12-2015, 04:18 PM   #9
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Quote:
Originally Posted by Punxsyjumper View Post

As a total newbie can someone define "porpoising"?
Porpoising | Henderson's Line-Up Brake & RV Inc.

Porpoising: What it is, and How to Stop It

A guy called me up the other day and told me his Dolphin motorhome was porpoising. I told him it sounded like it was having an identity crisis ().

Seriously though, porpoising is something we get quite a few calls on, and it is one of those terms that you hear about mostly with regard to RV’s. Porpoising is front to rear bounce; the front hits a bump, then the rear hits the bump, and they both bounce independently of each other, creating an oscillating motion. If the problem is severe enough, it can feel like you’re going to pull the wheels off the ground.

The problem is more typical in shorter coaches (low 20-foot to low 30 foot) than long ones. You don’t have as much trouble when you head up to 37 foot and beyond, and we definitely have more problems controlling it on a short wheelbase coach. The reason is that there is more time for the bump to settle out between the front and rear wheels on a longer wheelbase coach. Anything from the springs on down is called “unsprung weight.” The heavier your axles and tires are, the more difficult it is to make them change direction. Because of the high amounts of unsprung weight on a motorhome, it’s been a real challenge for us. Between the wheel, tire and brake, you’ve got 300 lbs. there, and when it’s spinning, it’s like a gyroscope; it doesn’t want to change direction.

Changing out your shocks and sometimes your springs will usually diminish the problem significantly. On some of the IFS coaches, our Motion Control Unit (MCU) can help cut down on porpoising as well. Sometimes controlling airflow into and out of the bags can help in some applications, but not always. For example, MCU’s on some Freightliners; we’ve managed to get the side to side movement out of it, but then it started porpoising. I had a guy with a Spartan IFS chassis that he cut down some porpoising by putting on the MCU’s on the front.

On non-airbag coaches, good shocks will typically do the trick provided you’ve still got some decent springs. In situations such as these, we use the Koni FSD, and for the ultimate, the RoadKing 2-5/16 bore shock. FSD’s are good for rebound control, and the frequency selective damping takes some of the harshness out of the ride. The FSD valve is a secondary valve that they put in the piston head that dissipates the initial shock load. Most shocks are a linear rate; the harder you work them, the stiffer they get. That’s an age-old dilemma; you can make anything handle well, but it can end up riding like a lumber wagon.

We were fortunate to be involved on the protoype testing on the RoadKing. When we first experienced these shocks on a P30 chassis, it felt like we pulled 20 psi out of the tires and improved handling at the same time compared to a competitive shock. We’ve been working with King shocks for three years. What we discovered with them is, the bigger the piston the more range of control, and the smoother the transition could be from small amounts of control to great control.

The RoadKing is a mono tube, high-pressure design which is the standard in high performance vehicles. It has the largest bore size on the market, so it has up to three times the volume of standard sized shocks. Standard pistons have 1.5 square inches of surface area; the RoadKing has 4.2 square inches—that’s 280% more surface area. The increased volume allows engineers to lower the required gas pressure in the cylinder, which gives you a smoother ride; the bigger piston also has more surface area to absorb the bumps. You also don’t have to run such tightly stacked disks in the piston head to control movement (check out roadking.com for more info). RoadKing shocks aren’t cheap, but they last longer than anything else and they’re also rebuildable. The Koni FSD’s are a 100 thousand mile shock; The RoadKings are run 350,000 or more in the trucking industry before requiring a rebuild.


Dr4Film ----- Richard
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Old 01-12-2015, 04:18 PM   #10
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As previously mentioned, it can be hard on ow hardware. Something else people overlook is tire balancing on a toad. You can get some serious vibrations going on when towing that you may not notice while driving your toad. I have seen some major damage done by towing vehicles with poorly balanced tires.Sounds like you need new shocks or other suspension work done on your RV.
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Old 01-13-2015, 12:26 AM   #11
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I've not had much issue with porpoising on a towed vehicle, simply because there are a couple joints in the tow bar system so the front of the toad doesn't get "worked" too badly. Trouble can really start if you're pulling a trailer with a fixed tongue. Depending on how much overhang you have on the back of the coach, your trailer can take a tremendous beating. Its especially true on anything in the rear of the trailer. It can get bad enough over time that the movement of the trailer will actually bleed down the lifters in my harley if its in the back of the trailer. That's a pretty common problem actually. The coach can be just fine, but if its "working" the trailer hitch very much, it can cause problems. The only real cure is slowing down.
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Old 01-13-2015, 07:34 AM   #12
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Your question comes just after I had the same thought while passing a MH the the other day. What I noticed that concerned me was that the tow bar was short and it was at a very steep angle. That being the towed end was significantly lower than the hitch end on the MH. Every time the MH porpoised, the front of the towed was lifted up, which requires a lot of leverage. Had the owner used a drop down hitch adapter to level the tow bar, this would reduce the upward pull on the tow bar and lessen the strain on the front mounts on the towed.

Like any trailer hitch, it should be as close to level or parallel to the ground as possible to allow for the maximum travel with the least amount of strain on both units.

This guys tow bar was at a 35-40 degree angle and that put the coupler on the end of the tow bar at a dangerous position on the hitch ball on the MH. I suspect over time the coupler will crack and the front end of his towed will too from the impact of the jarring from the bouncing of the MH caused by the MH porpoising.
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Old 01-13-2015, 09:09 AM   #13
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I am amazed at the number of RV's towing vehicles where one is significantly TOO high or TOO low for a safe tow.

If I happen to observe someone while parked I will explain to them what is wrong and why but 99% of the time it goes over their heads or they really don't care about the physics and off down the road they go.

The way I figure it if they have a problem it will be an expensive lesson and usually when it affects their pocketbook that's when a change will take place, hopefully.

Dr4Film ----- Richard
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Old 01-13-2015, 04:04 PM   #14
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If you have surge brakes on the toad, they may activate
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