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      03-20-2019, 12:05 AM   #1

Drives: '17 328d Wagon, '21 M2 Comp
Join Date: Sep 2016
Location: Bay Area, CA

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Bilstein B6 Shock Dynos

*Updated Info*
I recently stumbled upon ashiohsiao's FCM project thread in the 1-series forum where he went to Fat Cat Motorsports as well and got a set of custom tuned B6 based dampers for his RWD 118i. Based upon the data he posted of the RWD B6 damper dynos, I was able to compare it to my xDrive ones, and it looks like Bilstein is using the same damping for RWD models as well as xDrive. I guess that's not completely surprising given they use the same part number for all cars with a certain drive type (so one PN for all RWD and one for all AWD). Lazy...

*Original Post*
I recently received a set of Bilstein B6 front and rear shock/struts from Germany for a bespoke suspension project and dropped them off with my suspension builder this past weekend. He and I were interested to see how the B6s performed stock, so he put them on his shock dyno. Here's the plot:

What this shows is that that the rebound is much stronger than the compression in the front struts, which doesn't allow the strut to return to "normal" height after going over bumps, thus you lose ride height and "jack down." My suspension guru says that a bit more rebound over compression is desireable, but not the large ratios you see here. At the 2.5in/sec rate the rebound is 2.29x the compression force, and at 10in/sec it's still 1.94x higher. For the rears at the 2.5in/sec rate the rebound is 1.32x that of compression and 1.14x at 10in/sec.

Note that this graph doesn't zero out the nitrogen gas forces (42lbs front, 37lbs rear). These numbers are kind of high, and what that means is it takes a force of at least the pressure of the gas before the dampers will actually start moving and damping anything. This is typically why you feel more small/fine road textures with "sport" suspensions with high gas pressures vs a smoother ride. The dampers aren't actually doing anything/working in that regime!

The front PNs are 35-264583 (left) and 35-264590 (right) and the rears are 24-264570. I believe the rear shocks are available now in the USA, however the fronts never have been. These are the latest updated PNs (there was a recent revision) that are still pushed back to May for USA availability (and I'm fairly certain that date will get pushed back again). The front struts are what Bilstein recommends for all F30, 31, 32, 33, 34, and 36 xDrive cars, and the rear PNs are shared for all those chassis, and both sDrive and xDrive variants according to Bilstein's Euro catalog. It wouldn't surprise me if the sDrive front dampers have the same performance as these xDrive ones (given the rears are all the same across all models), and their PN differences are purely due to physical differences like the end link mounts on the struts.

Last edited by FaRKle!; 04-22-2020 at 03:19 PM..