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      11-08-2018, 02:12 AM   #2
ashiohsiao
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Drives: 2012 F20 118i
Join Date: Oct 2018
Location: Taiwan

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Shaikh (Fat Cat Motorsports) did a bit of over-time work just now and got some initial dyno testing on the Bilstein B6, as well as measured the gas pressure.

Just in case someone doesn't know what the gas pressure is, it is the force needed to make the damper begin compressing.

So the gas pressure for the Bilstein B6 (F20 118i):
Front: 48lbs
Rear: 54lbs

These are both way too high, and cause discomfort. Let's assume I hit a bump and it generates a force of 45lbs, my dampers' gas pressure will NOT compress at all, causing the impact to pass into the car directly (also lifting the car).

Below are the damping graphs of the dampers, with the upper portion as the compression damping, and the lower portion as the rebound damping.

This is the damping graph of the front damper:
Name:  F20 118i Bilstein B6 Front Dyno.png
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This is the damping graph of the rear damper:
Name:  F20 118i Bilstein B6 Rear Dyno.png
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When analyzing damping dyno, the usual practice is to remove the gas pressure from the graph, so both compression and rebound begin at 0. If you want to add in the gas pressure to see the net damping force, simply move the graph vertically upwards (both compression and rebound) by the gas pressure force.

Here are three pictures to illustrate how to read these graphs:
Name:  Picture1.jpg
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Name:  Picture2.jpg
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Name:  Picture3.jpg
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With gas pressure, I took some estimated readings:
Front:
Name:  Front with Gas Pressure.png
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Rear:
Name:  Rear with Gas Pressure.png
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Some observations that I made myself (haven't discussed with Shaikh to confirm my understanding):
- Starting at 6 inch/sec velocity, the front dampers start to have more rebound damping force than compression damping, causing jacking-down.
- Rear damper damping force is increasing quite linearly, which will make the suspensions unable to effectively deal with uneven road surfaces at high velocity

Last edited by ashiohsiao; 11-12-2018 at 03:32 AM.