New fifth wheel bounce when towing

[mtofell]

Need more weight in the airbags. 20# is barely anything. If they are like my Firestone's they will hold up to 90#. I usually run around 40-50#. When I run less I get the exact problems you are describing with excess bouncing. The bags essentially stiffen up the hinge at kingpin and stop the rythmic bouncing that can develop when hitting a bump.

[CecilD]

When a trailer goes over a large heave it tries to rotate around an east-west axis, creating the bouncing motions. Jacking up air bag pressure will help stop the trailer from rotating, however the trailer still wants to. The bouncing energy is still being generated. It can be dissipated by moving your truck up and down. Or, if your rear suspension is rock hard, it will be sent back to the trailer; hello frame welds.

Best to look at solutions that will reduce the trailer's tendency to rotate such as polar mass (increased pin weight), better axle equalization, or shocks on the trailer. A good air hitch will dissipate some of that energy. Some manufacturers quote 90%.

[mtofell]

Originally Posted by CecilD

When a trailer goes over a large heave it tries to rotate around an east-west axis, creating the bouncing motions. Jacking up air bag pressure will help stop the trailer from rotating, however the trailer still wants to. The bouncing energy is still being generated. It can be dissipated by moving your truck up and down. Or, if your rear suspension is rock hard, it will be sent back to the trailer; hello frame welds.

Best to look at solutions that will reduce the trailer's tendency to rotate such as polar mass (increased pin weight), better axle equalization, or shocks on the trailer. A good air hitch will dissipate some of that energy. Some manufacturers quote 90%.

What's the difference between stiffening up the rear of the truck with air or stiffening up the hitch point with air?

Also, I'm confused as to the term "polar mass" as it's being used. I can find no definition for this term that doesn't talk about Antarctica and polar bears.

[CecilD]

Originally Posted by mtofell

What's the difference between stiffening up the rear of the truck with air or stiffening up the hitch point with air?

Also, I'm confused as to the term "polar mass" as it's being used. I can find no definition for this term that doesn't talk about Antarctica and polar bears.

An air hitch doesn't stiffen the hitch joint, it softens it. Compare the movement of a Trailer Saver to a solid steel B&W hitch. An air hitch converts trailer generated energy into heat and radiates it into the atmosphere via the air bag sidewalls and shocks. A solid hitch transmits all the trailer's energy to the frame of the truck, and all the truck's bouncing energy to the frame of the trailer.

Polar mass refers to having weight at the ends of the trailer rather than over the axles. That is why filling a water tank or heavier pin weights tend to reduce chucking in fifth wheels. I first read about it when Porsche introduced the 928 with the rear transaxle. They claimed front engine/rear transmission increased polar mass and reduced the car's tendency to rotate.

From the Latin "Polus", end of an axis.

[kdauto]

Originally Posted by CecilD

An air hitch doesn't stiffen the hitch joint, it softens it. Compare the movement of a Trailer Saver to a solid steel B&W hitch. An air hitch converts trailer generated energy into heat and radiates it into the atmosphere via the air bag sidewalls and shocks. A solid hitch transmits all the trailer's energy to the frame of the truck, and all the truck's bouncing energy to the frame of the trailer.

Polar mass refers to having weight at the ends of the trailer rather than over the axles. That is why filling a water tank or heavier pin weights tend to reduce chucking in fifth wheels. I first read about it when Porsche introduced the 928 with the rear transaxle. They claimed front engine/rear transmission increased polar mass and reduced the car's tendency to rotate.

From the Latin "Polus", end of an axis.

I never heard the term "polar mass" but I have heard of "polar moment". Oddly enough I too remember this when referred to the 928, probably some Car And Driver review or similar.

Polar, or (from the Poles, North or South) and moment meaning the time for motion to occur. In the 928 the were referring to the oversteer factor (delay time).

In your 5th wheel reference I imagine we are talking about the side-to-side rocking of the 5er on the truck OR the "chucking" effect on improperly hitched 5ers. Chucking is the samefeeling as if you'd be "pumping" or pedalling the accelerator.

I'm just putting this info for the ones wondering what the heck we are talking about.

[tuffr2]

When I think of polar mass as it relates to the OP's issue I think of 'Balance'. The 928 was trying to be a 'well balanced' car. Front to back as well as side to side.

So one thing that may help the OP is to 'balance' his 5th wheel if possible.

[redfisher]

I'm the OP and would like to thank you for all responses. Some questions have been asked so I'll provide some addt'l info.


Front axle rating - 5200#
" " scale weight - 4820#
Rear axle rating - 6200#
" " scale weight - 5840# (the rear axle weight with the truck loaded for camping is 3380#, making the pin weight 2460)

GVWR - 10,000#
GVW scale weight - 10,660#


Max tire load for truck is 6380# at each axle.



Scale weights are with all gear and occupants, no water in any holding tanks


I realize I'm over on GVWR .


The trailer does not have shock absorbers but does have the Moryde suspension installed at the factory. It's a 2011 Cameo 34SB3 model.


Does anyone know how to assess wear on that suspension system ?


I will install new shocks on my truck. I will look into having shocks installed on the trailer( my last 5er had them)


Thanks again for your responses.


Bill

[Super Thirty]

I recently had the wheels aligned on my travel trailer. Before the alignment the trailer always felt like it was surging behind the truck and it felt like it was porpoising. I switched to an Andersen Hitch and that improved it immensely but the wheel alignment eliminated it completely. My wife says she really noticed the difference. While our trailer is not a fifth wheel I’ve found sometimes the problem occurs from a combination of things not just one.

[NvGuy]

The only way I know of to assess wear is to remove the spring and equalizer bolts to visually inspect the bushings. The best time to do this is when the coach is on jack stands for a brake inspection & wheel bearing inspection / repack. You can jack the coach up to remove the weight from the equalizer then see how much vertical movement there is, but this isn't very precise.
If the coach has wet bolts-and-(this is the catch) they were regularly greased then there should be minimal wear. No grease = accelerated wear.

[redfisher]

Originally Posted by NvGuy

The only way I know of to assess wear is to remove the spring and equalizer bolts to visually inspect the bushings. The best time to do this is when the coach is on jack stands for a brake inspection & wheel bearing inspection / repack. You can jack the coach up to remove the weight from the equalizer then see how much vertical movement there is, but this isn't very precise.
If the coach has wet bolts-and-(this is the catch) they were regularly greased then there should be minimal wear. No grease = accelerated wear.

Thanks for your response. I have auto levelers so I should be able to check them easily. I'm not sure if the system has wet bolts, it's new to me and currently in storage away from my home but I'll check it out.


In your opinion, if the Moryde system is in good shape, do you think adding shock absorbers would be of much benefit given my situation with the bouncing?


Thanks,
Bill

[Fulltimer]

If you have the Moryde IS system, you have shocks.