I am just guessing that your shocks are hitting the bumpstops. I would think that a lowered car going over a street bump could cause the shock to bottom out.

My Porsche technical support guru has been installing Bilstein shocks on Porsche's for years and has seen that the Bilsteins when set low for the track, don't have enough travel. He called an engineer at Bilstein and got him to tell us how much overkill was in the bumpstops in the Cayman PSS9 shocks.

We were able to disassemble the shock and cut the stops down almost in half. Gave me plenty of travel for the track and street even after lowering the car about 40mm.

I would not do this, unless you know what you are doing. Find an old school Porsche race car builder, who can take the Bilsteins apart. If you need specs on how much of the bumps stop you can cut out, let me know and I will make some calls.

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