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Thread: Matching Springs to Load Carried
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05-16-2019, 07:00 AM #31
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Hi Rob, thank you for your work on the spring info. Just swapped my kitchen side to 3000# on my 303 per your info.
Question. You had mentioned that the OEM on axles were concerned about natural frequency and using an unmatched pair of springs (3000# one side and 2700# on the other) would cause issue. Do you have any more info in this area of study? Just curious.
TIA
TTThank you!
2021 310GKR Solitude
2022 GMC Denali - Duramax
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05-16-2019, 07:24 AM #32
Hi TT,
Quoting from an earlier discussion . . . see this thread https://www.mygrandrv.com/fo...525#post103525 . . . particularly around post 54.
"LCI will claim (at least they did to me at the Rally tech session) that they can’t have different springs because this will create an imbalance of spring natural frequencies side-to-side. They seem to be forgetting that natural frequency is affected by the weight carried by the spring. Not to get too deep into the math, but natural frequency varies directly as the spring constant and inversely as the mass, so increasing the strength of the spring will actually compensate somewhat for the increase in weight, keeping the natural frequencies closer together. Whether the natural frequencies should or should not be matched in a four spring undamped system is way more math than I am up for "
RobCate & Rob
2015 Reflection 303RLS
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05-16-2019, 08:05 AM #33
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. Thank you!
Thank you!
2021 310GKR Solitude
2022 GMC Denali - Duramax
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05-16-2019, 08:51 AM #34
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Rob,
I am in full agreement with you (previous discussions). I found this calculator for a coil spring but I think the concept of different weight on a spring changing its natural frequency rings true. With that said, putting more weight on a heaver spring will give it the same Natural Frequency as a lighter spring with less weight on it. So with us putting different springs on 303's to compensate for the weight difference side to side solves the Natural Frequency problem that Lippert created by not using different springs side to side.
So to kind of prove the point I used this calculator for a 2600 lb./in spring and a 3000 lb/in spring. https://www.amesweb.info/Vibration/N...of-Spring.aspx
Values
2600 lb spring
Spring constant [k] = 2600 (lbf/in)
Mass [M ] = 2600 (in) Used 2600 to simulate 1" of spring compression
Resulting First natural frequency [f1] = 3.127 HZ
3000 lb. spring
Spring constant [k] = 3000 (lbf/in)
Mass [M ] = 3000 (in) Used 3000 to simulate 1" of spring compression. My 303 has about 400 lbs of extra weight on the drivers side.
Resulting First natural frequency [f1] = 3.127 HZ
Hmm, same natural frequency. So if I'm thinking correctly, putting different size springs side to side actually helps correct natural Frequency issues. Just as we think.
Try putting different weight on the 2600 lb spring in the calculator and watch the Natural Frequency change.
Another Gearloose moment,
PatLast edited by Gyro Gearloose; 05-16-2019 at 08:56 AM.
Pat&Marlene Gyrogearloose - 2010 Itasca Meridian 34y - 6.7 w/Allison 6spd - Jeep Wrangler Rubicon - previous Reflection 303RLS
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05-16-2019, 09:10 AM #35
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05-19-2019, 07:29 PM #36
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Looking this up was easier than cracking my Vibs book.
Natural frequency of spring mass system
A spring does not have a natural frequency of its own. The natural frequency of a mass spring system depends both on the stiffness of the spring and the mass of the body supported by the spring and is f=1/(2pi)*square root (k/m) where k is the stiffness of the spring and m is the mass.Last edited by MidwestCamper; 05-19-2019 at 07:35 PM.
MidwestCamper
Jim & Dawn
Near Milford, Michigan
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