So I blew a B6 (HD) in a pothole the other day. Ordered new front B8s (sports) from Tirerack (on sale vs. the B6).
Unfortunately, I was in a rush, so I didn't pull the cartridge/bump stop out of the B8, but the housings, shaft lengths, and stroke appear to be identical between the two.
So the widely asserted "body is 25mm shorter" isn't correct. Pics:
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'02 S54 M3 (500/500 GC/Koni)
'08 N54 135 (JB4, DCI, BMW PS/Bilstein B6s, H&R M3 FSB, Strongflex FCABs)
'14 N55 X1 (JB4, BMS DP, BMS Intake, Alpina TCU reflash, H&R Sports, Bilstein B6s, E93 M3 RSB, Strongflex FCABs, baby seat)
'08 N54 535xi touring (Bilstein B6s, Downpipes, MHD tune, baby seat)