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Sprinter RV's & Conversions Talk Common features found in Sprinter RV's and Conversions.


 
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Old 12-27-2016, 05:07 PM   #1
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Default Sway Bars vs. rocking ... no bull

It's really amazing how some people perceive suspension modifications. Some think sway bars are the best suspension mod. If that's actually the case then why wouldn't Mercedes install their biggest SB? The reality is that sway bars reduces sway but significantly increases rocking. Not all "good" comes from bigger sway bars.

Here's some accelerometer data from my Winnebago Navion motor home going over a speed bump at an angle with and without the sway bar attached. The yellow plot represents vertical movement. This plot is not affected by SBs. Likewise the blue plot (front-to-back movement) is not affected by SBs. The pink plot shows side to side movement, or rocking. With the Hellwig SB, accelerometer measurements show peak amplitude of 125 units after the rear wheels hit the bump. Removing the SB, peak amplitude reduces to 60 units. The difference between no SB and a Hellwig SB about as twice as much rocking.

I converted the accelerometer plots into FFTs (Fast Fourier Transform). The x-axis changes from time to frequency. The rocking frequency is just under one Hertz. The y-axis displays the energy of oscillations. The energy of the Helliwig SB at 1 Hz is almost double that of the no SB configuration. That is significant!

A bigger sway bar will increase rocking. The only way to counteract rocking is with dampers. The best dampers I've found are modified Fox shocks sold by Agile Off Road.
Attached Images
File Type: jpg Hellwig SB.jpg (75.1 KB, 225 views)
File Type: jpg #9 No SB.jpg (67.6 KB, 203 views)
File Type: jpg FFT Hellwig SB.jpg (33.7 KB, 282 views)
File Type: jpg FFT no SB.jpg (31.3 KB, 271 views)

Last edited by calbiker; 12-27-2016 at 05:10 PM.
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Old 01-02-2017, 08:00 PM   #2
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Default Re: Sway Bars vs. rocking ... no bull

So... I'm getting confused... but I'm trying hard to understand this because you are son convincing (and seem well-versed in how to prove your suggestions). Forgive me for being repetitive, but some of the confusion comes from the lengthy discussions that move into other side-line discussions.

Can it be put succinctly?
1) To improve body movement in high-winds or when large trucks pass by on the Interstate... use what?
2) To improve abruptness of ride over potholes or rough surfaces... use what?
3) To improve rocking over approaches to angled driveways or speed-bumps... use what?

I get the feeling from my reading that trying to correct for one of these, increases the problems with the other two.
If I had to choose, I'd opt to get improvement with Item 1.
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Old 01-03-2017, 05:28 AM   #3
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Default Re: Sway Bars vs. rocking ... no bull

As much as I like to see the creativity that goes with these sort of posts, I cant help but wonder about all the $quillins of Euros that Mr Mercedes and Mr Benz must have wasted with all the research only to be found out to be wrong by a weekend warrior?
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Old 01-03-2017, 04:39 PM   #4
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Default Re: Sway Bars vs. rocking ... no bull

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As much as I like to see the creativity that goes with these sort of posts, I cant help but wonder about all the $quillins of Euros that Mr Mercedes and Mr Benz must have wasted with all the research only to be found out to be wrong by a weekend warrior?
Entirely true - if you are looking at a van conversion. The minute you slap a coach body on the back of a cab chassis Sprinter the MB engineering research takes a back seat.
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Old 01-03-2017, 06:32 PM   #5
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Default Re: Sway Bars vs. rocking ... no bull

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Entirely true - if you are looking at a van conversion. The minute you slap a coach body on the back of a cab chassis Sprinter the MB engineering research takes a back seat.
Obviously the more weight you add the more leaves you will need in the rear springs to compensate, hardly a MB fault if you overload from engineered specs.
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Old 01-03-2017, 07:52 PM   #6
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Default Re: Sway Bars vs. rocking ... no bull

Quote:
Originally Posted by Tooth Fairy View Post
As much as I like to see the creativity that goes with these sort of posts, I cant help but wonder about all the $quillins of Euros that Mr Mercedes and Mr Benz must have wasted with all the research only to be found out to be wrong by a weekend warrior?
I think you are reading the data wrong.
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Old 01-03-2017, 08:04 PM   #7
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Default Re: Sway Bars vs. rocking ... no bull

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Originally Posted by Tooth Fairy View Post
Obviously the more weight you add the more leaves you will need in the rear springs to compensate, hardly a MB fault if you overload from engineered specs.
Fully agree but many of these sway bar queries/threads are coaches and not vans. More than one of the respondents above are in cab/chassis coaches and not vans. Mother Benz engineers did what they could and I don't place any blame on them at all.
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Old 01-03-2017, 08:11 PM   #8
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Default Re: Sway Bars vs. rocking ... no bull

Quote:
Originally Posted by Scarecrow View Post
Can it be put succinctly?
1) To improve body movement in high-winds or when large trucks pass by on the Interstate... use what?

A larger sway bar and/or Fox shocks. Fox shocks have enough damping to decrease body sway caused by passing trucks. However, nothing will be perfect. Sway will be reduced by a sway bar or better damping, it will not be eliminated.

2) To improve abruptness of ride over potholes or rough surfaces... use what?

Shock absorbers with more damping. The best shocks I've found are Fox shocks for Jeeps, modified by Agile Off Road.

3) To improve rocking over approaches to angled driveways or speed-bumps... use what?

Same as #2

I get the feeling from my reading that trying to correct for one of these, increases the problems with the other two.
If I had to choose, I'd opt to get improvement with Item 1.
As mentioned, you can reduce #1 but not fully. I would try better shocks (Fox @ $260/pair) first.

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Old 01-03-2017, 09:41 PM   #9
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Default Re: Sway Bars vs. rocking ... no bull

I guess it takes a weekend warrior to tell Mr Benz his Sprinter suspension is not up to the standards of past "German engineering".

If you had a 8 ft long beam and need to balance and stabilize it at two points, you would choose the two locations at the ends of the beam. The closer towards the center the two stabilizing points become, the more difficult the job becomes. Right? So why would Mr. Benz mount the stabilizing points 8.5 inches from center? You're getting into a situation where the shocks can't control rocking. And adding a bigger sway bar just amplifies the already bad rocking.

Quote:
Originally Posted by Tooth Fairy View Post
As much as I like to see the creativity that goes with these sort of posts, I cant help but wonder about all the $quillins of Euros that Mr Mercedes and Mr Benz must have wasted with all the research only to be found out to be wrong by a weekend warrior?
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Old 01-03-2017, 10:28 PM   #10
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Default Re: Sway Bars vs. rocking ... no bull

How many leaves have you got in the rear springs?
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