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Suspension often requires different ranges of behavior. Small amplitude and high sensitivity for vibrations and small sharp bumps but also high amplitude and low sensitivity for larger smoother road deformation. So my question is whether or not it's possible to use two suspension system on top of the other. I was thinking of a small fast shock (strong spring with weak damper) for small amplitude/high frequency and then a long slow shock (weaker spring with a stronger damper) for high amplitude/low frequencies.

My main concern is of course interactions between them.

Do you have any example of this setup?

Thanks

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    $\begingroup$ All cars have this setup, see the wheels act as a second spring mass system. But yoir much better of using active suspension. $\endgroup$
    – joojaa
    Oct 11, 2017 at 15:01

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There are manufacturers of progressive springs - soft for the first part of the movement then harder for the rest of the travel.

There are also shock absorber manufacturers that make various types of shock - depends on the applications you want and what is available "off the shelf" ie fairly standard or you can go to them with your requirements and they will make them to your specifications (for road use within limits, off road ....), but they won't be cheap..!!

Edit: also check out Citroen for hydraulic suspension (variable) and the older mini for hydrolastic... and also landrover / Range rover for adaptive settings...

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  • $\begingroup$ The use case I was thinking of is mountainbike. So electronic suspension might be hard to implement. $\endgroup$
    – bokan
    Oct 13, 2017 at 13:44
  • $\begingroup$ That detail : mountain bike would be useful in the question. avoids people making suggestions that will be irrelevant. $\endgroup$
    – Solar Mike
    Oct 13, 2017 at 13:51
  • $\begingroup$ Don't worry, I'm interested in the general purpose question and the theory of suspension systems. Thank for your answer. $\endgroup$
    – bokan
    Oct 13, 2017 at 13:53
  • $\begingroup$ The shocks on my son's downhill bike have various valves that can be set so compression and extension behave differently $\endgroup$
    – Solar Mike
    Oct 13, 2017 at 14:13
  • $\begingroup$ Yet, I do too, but those suspensions still have only one spring. $\endgroup$
    – bokan
    Oct 13, 2017 at 15:00
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The short answer is 'yes,' since each absorber has its own frequency response curve.
Now, the ideal setup is an active absorber with, say, piezo-driven adjusters which respond to the initial impact profile. There is a prototype out there somewhere of an active sensor which is designed to recognize road bumps and essentially turn off all damping, so that the wheel assembly goes up, over, and down the bump without transmitting any vertical force to the car body. More gentle (less delta-functionish) bumps are treated differently, to keep the overall ride as smooth as possible.

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My answer will probably sound simplistic, but examples of this are more common than people think - the spring/damper arrangement of most vehicle suspensions, coupled with a pneumatic tyre, does exactly what you're describing (tyre = low amplitude high frequency, spring/damper = high amplitude, low frequency).

[I think joojaa was thinking along similar lines, and any wheel with a damped elastic response will have this effect.]

There are much smarter ways of doing it, as Mike and Carl have indicated.

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