Why more shock rebound vs. compression damping ?

[TrackRat]

For those who tune suspensions for a living, why is it common to use more rebound shock damping than compression damping, particularly at lower velocities say under 6"/sec.?

 

[GregLocock]

Because the tire is already having to accelerate itself, and the sprung mass (via the spring) upwards, adding more damping force just makes the impact worse. You might find on a track that that ratio drops somewhat.

The ideal magic carpet ride would maintain equal vertical force across each axle. Every time you upset that you want to do it as gently as possible.



Cheers

Greg Locock


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[TrackRat]

That's what I understood also. It seems that some damper companies have found that adding compression force (above critical damping) below 2"/sec. (increased nose damping force), prevents the unsprung mass from over-shooting and requires less overall compression and rebound damping to control the suspension motion at higher velocities without increased transmissibility, thus a better ride and better motion control.

 

[TrackRat]

I'm wondering if adding compression damping below 2"/sec. is in the range of suspension bushing compliance and thus people don't sense the increased damping force but the result is less suspension motion over a bump and less roll which improves transient response?

 

[TrackRat]

I found some useful info. on bump vs. rebound damping at OptimumG. I won't be using (10) shocks on my street vehicle however... *LOL*

http://www.optimumg.com/OptimumGWebSite/Documents/TechTips/Springs&Dampers_Tech_Tip_4.pdf

Comments welcome on the OptimumG Damper/Spring Tech Tips.

 

[cibachrome]

Higher rebound damping is an effective way to buy more ride travel without having to actually have it.

 

[TrackRat]

Yeah, I can see how using more rebound damping as a bandaid for insufficient suspension travel is possible.

 

[hemipanter]

What I say here is a theoretical argument and no specific indications. We have a sprung and unsprung carweight that in high and low speed dampening requires a certain amount of damping. This amount of dampenig is to be divided between compression and expansion of the proportions to suit car use. For an ordinary car is the idea to have smaller compressions damping and thus the corresponding part more expansion damping. This is to get better comfort as hard compression damping gives a jerky ride.
For a racing car it is not good to use more expansion damping because the wheel is prevented from rebound fast enough after it crossed a ridge in the road, then you lose grip. Hard compression does not matter to much, since comfort is not so important.
Now there are racing situations where more expansion damping is used to make the car lower, so the distribution of attenuation in question is an adaptation to both the track and rules.
Goran