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Old 04-10-2016, 02:34 PM   #1
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Default Half-Car suspension simulation

The bilsteins on my car feel extra dead... probably because they have 200k miles on them. So I've been digging through the site looking at damper information trying to make a somewhat informed decision on what to do about the situation (revalve, illuminas, agx, etc) and I have had a hard time finding solid info that quantifies what damping you need for certain spring rates. This is my first NA miata and before this I only drove subarus, so I also lack experience in how a miata should feel on the road (but I can assume it should feel like a normal car, and not a spine smooshing mobile)

FCM has a lot of good information and I've been trying to couple that with what I have learned in enginerd school. Sooo I used Matlab to create a half-car model of a miata, using some of FCM's data from this source: FCM_MSDS_1_8NA.xls. Damping rates were sourced from another Shaikh post here: MX-5 Miata Forum - View Single Post - Teaser: FCM adjustable perch/spring kits and full coilover suspensions coming soon!.

The model takes into account the vehicle mass, weight distribution, tire and suspension spring rates, and suspension damping rate (Bilstein HDs). However, its all an approximation, and doesnt take into account suspension friction, varying damping rates, hysteresis, and varying road profiles.. and all other real world things that I'm missing...

My main gripe with it right now is that the compression and rebound damping use the same value, for some reason when I try changing it to specific compression and rebound values Matlab becomes unhappy.

Here is a plot of suspension deflection of the front and rear driving over a 2" triangular bump at ~22mph. This is using spring rates for a 1994 with Bilstein dampers.

I think this is a good plot to demonstrate what Shaikh refers to as "flat ride"; at about 1.25sec the front and rear deflection is sync'ed and from there on they deflect in almost the same way.

I can get deflection, force, velocity, and acceleration data from the model, but as I mentioned it is still quite flawed at the moment. I hope to get it to the point where I can enter in models of specific dampers and spring rates and get some useful plots for how one can expect the system to behave.

Also I'm using metric units, so deal with it.

Also here is a link to the model sketch: http://i166.photobucket.com/albums/u....19%20AM_1.png
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Half-Car suspension simulation-initial%2520miata%2520half%2520car.png   Half-Car suspension simulation-977ee0fb-34d2-489c-a21a-ab6b05c3fb06.png  
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