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      11-15-2012, 03:35 PM   #5
The HACK
Midlife Crises Racing Silent but Deadly Class
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Drives: 2006 MZ4C, 2021 Tesla Model 3
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I attended a TechFest West seminar hosted by Jay from Ground Control, and he has shock dyno charts that showed OEM Sachs dampers losing 50% of its effective damping by 30,000 miles, and by 50,000 miles they were down to 10%.

HAVING SAID THAT. Unless you're comparing shocks and struts of the same part number, it's hard to tell for sure what's going on between the old and new shocks. BMW has traditionally spec'ed shocks with higher rebound than necessarily for the rear. Again, I had some conversation with Steve Dinan at the same TechFest West back in 2004, and he said that on his stage I kits he actually DECREASES the rebound on the rears of most of his kits to make the car behave better in corners AND ride better. The fact that the new shocks returned to the full and upright position quicker may just mean it's tuned to provide LESS rebound control.

When I installed my Koni single adjustable tubes on the WRX, I purposely played around with the rebound setting before I installed it on the car, and surprisingly, at the "stiffest" rebound setting, the shocks took forever to return to fully extended, while at the "softest" setting the shocks returned to extended range with relative ease. So what you're seeing may be indicative of Bilstein choosing to reduce the rear rebound compared to factory setting, or at 30,000 miles, your shocks may be far less effective than they originally were.

Try this unscientific test. Once you compress the shock's piston fully, try and pull it back out rather than letting it slowly expand. If you can pull it up easily, then it's done for. If it still provides plenty of resistance to you pulling the piston back out to fully extended, it may just be designed to provide high rebound rate rather being busted.
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