Specifying damping from models and data

It sounds like you are doing something a lot more complex than the way I would go about it. A typical plot of "sprung mass response to road input" transmissibility indicates that a damping ratio of anywhere from 0.2 to 0.4 is a good compromise. For the 1958 Jaguar XK150S the front suspension (w/o ARB) critical damping calculates out to be 29.1 lb-sec/in, which means the damping coefficient should be around 8.73 lb-sec/in, and not the 5.6 lb-sec/in I was initially using. The 5.6 lb-sec/in gave me a high peak transmissibility value around 12 (!!), and now I know why. I'm going to have to re-run the transmissibility equations (from Gillespie's "Fundamentals of Vehicle Dynamics", page 150) again, but I think I will see a fundamental improvement. By the way, the "sprung mass response to sprung mass input" transmissibility equation (Eq. 5-17) has a typo in my 1992 edition of Gillespie's book; the odd symbol in the equation numeratior should be a Greek lower case "chi" for "unsprung mass to sprung mass ratio". Both that transmissibility equation, and the response to road input equation, work out very well for me, but the "sprung mass response to unsprung mass input" is completely wacko. You wouldn't know of any corrections to the equation, would you? I sent an inquiry to the great man himself, but who knows if I'll get a response. I tried checking with Dukkipati (et al) in his book "Road Vehicle Dynamics", but he only shows the two transmissibility functions that I already know to be correct. A literature search came up with more of the same, plus a transmissibility function for "unsprung mass response to road input", which is very good thing to use for road holding determinations, but still not what I need....BPW

Im not familiar with the Gillespie book to honest. Its neat that you tried to get a hold of him though. Thank you for presenting your method!

The reason Im not using just sprung output over road input is that it leaves out whats actually going on at the contact patch which for the moment is what I am after. Body control is important especially for aero setups critical to ground clearance as well as ride comfort, but thats not my main focus with this.

Im literally using load fluctuation at the road surface for a ton of different frequencies in the form of a body plot and defining the road based upon a power spectral density (there are a number that define varying road conditions). That allows me to weigh the importance of each frequency to the system as 20kHz is probably not pertinent nor is .01Hz (which wouldnt give much response anyways). The sensitivity of load fluctuation at that frequency to damping ratio will also be given weight.

At the end of the day damping needs to be different in both directions and at least modeled as varying with velocity (non-linear) so this is merely a ballpark like I said.

The problem im having is finding a way to find a particular curve of damping that varies with velocity bi-directionally and is solved for minimal load fluctuation (area under the gain curve). This ignores the concept of driver control through low speed damping and many others considering its only a quarter car, but that can be ironed out in later refinements.