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      06-17-2008, 05:28 AM   #23
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Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

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Originally Posted by jm1234 View Post
Perhaps I should be more clear, I think it is fair and valid to conclude that the "system is going to be robust to changes in spring rate" (it is actually guaranteed because even stock spring have some variability) but you do so without attempting to put bounds on the statement. I'd bet the N54 engine is robust to changes in boost pressure too. Surely you don't believe that was a system design criteria and/or that any spring rate or type will work just fine? It's a question of degrees and nobody seems to want to put any numbers to any of the changes discussed.

The conclusion that the system is robust to changes in damping when damping is the controlling variable is nonsensical. The damping rate is clearly designed to change and to do so over a much greater range than a traditional damper so the comment doesn't make sense when placed in the same context as the spring rate which is not designed to change.

I wish you luck with your modification and if you say that the specific springs installed do not ruin the ride I'll take your word for it. I still think that the system will not take any spring rate and that some spring rates will cause a crappy ride regardless of the system. I also think that the effect on damper life is an open question as no one can describe any of the pertinent design elements of the system (like how the dampers or control systems work) let alone analyze their interaction.

By dynamic system offset I'm simply referring to the offset over a known period of time. In other words, the system can calculate with a certain degree of error and over a fixed period of time what the relative (from the start of the time period) position offset is based on accelerometer readings.

By static system offset I'm referring to a measurement of the system offset with a certain degree of accuracy without regard to time. Basically you wouldn't be able to do this with an accelerometer because the buildup of position error over time would overwhelm the position measurement.
-I even guessed at some bounds on the spring rates and stated that before. My guess was basically anything that any reputable spring manufacturer would build for the car for anything outside of dedicated track/race car.

-Just FYI, I do not plan to change the springs on my own car. All is just fine and BMW have done a darn good job of compromise IMO.

-It is not really nonsensical. You could easily design a simple suspension system that actively controlled damping that was not robust to the allowed range of damping. Would it make production, no, could it be designed, yes.

-I more or less agree with you clarification of what types of offsets an accel can and can not measure.

OC: There is an inherent problem asking folks who design springs (coils and torsion bars) for their opinions on the suitability of their own products for certain applications. There is not only possible conflict of interest but there is a serious question of expertise.