Here are a few dyno curves for the various Bilstein shocks available for the BMW E36 chassis. The dyno runs were generously supplied by Mike O'Callaghan of Shocktek, Inc. located in Girard, PA. 1-814-774-8808.
This is a comparison plot of all three front struts. I think this will be very interesting to some people.
These plots show left and right front struts for each of the three types.
This is the left and right rear M3 HD shocks.
Note that on all plots, rebound damping is in the right upper quadrant, compression damping is in the left lower quadrant.
These pages will be updated with comments and analysis soon. I wanted to get the plots out so people could have a look at them though. The three struts I've gotten done so far are the E36 HD and Sport, and the M3 HD. The first two are twin tubes and the M3 units are monotubes. Also have the M3 HD rear shocks.
The data were collected on Shocktek's MTS 810 servo-hydraulic test stand. This is a pretty amazing unit, capable of putting out 3500 lbs. of force over a 5" stroke.
It is fitted with a position sensor and a load cell (force). Various wave forms can be played through it simulating a wide variety of shock and vibration inputs. The ram can be commanded to precisely track either a position or force input wave form, yielding extremely accurate inputs. Position input waveforms are used for these plots and force is measured as output. The position sensor is used both to record data and to run a closed-loop controller forcing the ram to track the input waveform.
In case you want to know, this is a $120,000 piece of hardware. I have used Mike's system extensively for some of my electronically-controlled suspension system design work for NAVAIR and other DOD clients.
The data collection method was as follows: the bottom of the shock/strut is mounted to a fixture on the end of the hydraulic ram. The top of the shock/strut is bolted to the load cell via another fixture which is rigidly attached to the frame of the MTS. The ram is then offset to the mid point of the shock travel. A low frequency sine wave (@?? Hz and ?? inch amplitude) is played through the MTS and the analog signals from the position sensor and load cell are recorded on a National Instruments/LabViews-based data acquisition system, and converted to proper units. This yields a digitized force/position data set. The position data is then differentiated with respect to time, yielding a force/velocity data set. This is what appears in the plots.
Some caveats: This is fairly raw but very accurate data. Many shock dynos use some very crude methods to approximate velocities, and then only plot a small number of points and then connect the dots. The data here represents a full range from roughly -12 to 12 inches/second. The Bilsteins are high-pressure gas shocks, and so there is a static gas spring force which will make the curves look weird if it is not removed. So this offset force was measured at the mid point of travel for each shock and subtracted from the force data. There are still some slight gas spring effects seen in the plots, this is due to the difference in compression of the gas at the peak and valley of each sinusoidal motion. We could have removed that too, but since it is a true dynamic force, it is real information describing how the shock works.
There are a few other weird forces in the plots, mainly due to seals. These tend to be directional and may go away as the shocks break in. All the shocks were new units, and were warmed up to operating temperature prior to recording data.
As soon as I get the struts and shocks off of my 95 M3, I'll have those dynoed as well and add the curves. I'll be adding lots of other stuff related to tuning the M3 suspension over the next few months.
Comments and suggestions are welcome. Please feel free to contact me at
Finally, any comments regarding Bilsteins and shocks in general are my own and do not necessarily reflect the views of Shocktek or its employees.
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This page was last updated on 04/28/99.