Porsche 997 PASM suspension compression measurement.
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Porsche 997 PASM suspension compression measurement.
I’m looking for a measurement from any owner of a 997 with PASM, for comparison with my own cars track setup and a resto mod project
I would like to know how much the stock PASM Rear Shock absorbers compress when the car is lowered to the ground, to be able to establish the millimetres of compression and rebound that Shock has available in its travel, and how much is already used by ‘sag’ at rest.
(Sag or Droop, either terminology)
Best measured when the car is on a hoist, simply from the lip of the bodywork to the edge of the rim, then lower the car to the ground and repeat - this would be how much the springs sag due to the static weight of the car.
(Using a hoist is best, as jacking just a single side the sway bay will deflect some of the travel) *yes, measuring directly on the shock would be best, but trust me, it’s not easy to crawl under these cars and measure without a platform hoist.
My measurements of PASM REAR shocks have a total travel range of ~120mm, but the bump stop seems to take up ~25m of this, so there’s only -95mm of range. I’m wanting to know if the shock sits Half Way, ie has roughly half (47.5mm) of compression travel before it hits the bump stop, and similarly 47.5mm for droop that can extend.
Or is the ratio different, the shock compressing more are rest, sitting closer to the bump stop, but having more extension distance to keep tyre contact on rough roads? (Eg compressing 60mm).
The manuals quote the PASM Rear Spring rating as 56 N/mm
And with roughly 420kg on each rear corner the predicted static compression distance calculates to 75mm from the weight of the car, but that doesn’t take into effect how must the spring is preload compressed in assembly - and why you must always use spring compressor tools when disassembling shocks to change dust boots etc.
My own 997 I’ve converted to Cup hubs front and rear and Sach shocks with H&R springs for track days, vastly stiffer springs with a much shorted travel, and helper springs to keep the main spring perched.
The resto mod project uses 997 suspension but appears to only be compressing 31mm when I lower the car, which doesn’t seem right at all. So I’m trying to trouble shoot if I have a stuck PASM valve or otherwise whilst I set the car’s ride height (via shims above the shock at the tower).
I would like to know how much the stock PASM Rear Shock absorbers compress when the car is lowered to the ground, to be able to establish the millimetres of compression and rebound that Shock has available in its travel, and how much is already used by ‘sag’ at rest.
(Sag or Droop, either terminology)
Best measured when the car is on a hoist, simply from the lip of the bodywork to the edge of the rim, then lower the car to the ground and repeat - this would be how much the springs sag due to the static weight of the car.
(Using a hoist is best, as jacking just a single side the sway bay will deflect some of the travel) *yes, measuring directly on the shock would be best, but trust me, it’s not easy to crawl under these cars and measure without a platform hoist.
My measurements of PASM REAR shocks have a total travel range of ~120mm, but the bump stop seems to take up ~25m of this, so there’s only -95mm of range. I’m wanting to know if the shock sits Half Way, ie has roughly half (47.5mm) of compression travel before it hits the bump stop, and similarly 47.5mm for droop that can extend.
Or is the ratio different, the shock compressing more are rest, sitting closer to the bump stop, but having more extension distance to keep tyre contact on rough roads? (Eg compressing 60mm).
The manuals quote the PASM Rear Spring rating as 56 N/mm
And with roughly 420kg on each rear corner the predicted static compression distance calculates to 75mm from the weight of the car, but that doesn’t take into effect how must the spring is preload compressed in assembly - and why you must always use spring compressor tools when disassembling shocks to change dust boots etc.
My own 997 I’ve converted to Cup hubs front and rear and Sach shocks with H&R springs for track days, vastly stiffer springs with a much shorted travel, and helper springs to keep the main spring perched.
The resto mod project uses 997 suspension but appears to only be compressing 31mm when I lower the car, which doesn’t seem right at all. So I’m trying to trouble shoot if I have a stuck PASM valve or otherwise whilst I set the car’s ride height (via shims above the shock at the tower).
Last edited by LoganMarriott; Jan 21, 2025 at 04:16 PM. Reason: noting Rear Shock for measurement
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