PASM and lowering springs

I had a conversation with a Porsche engineer this weekend through a contact of mine. This particular engineer works on suspensions, let's call him 'Hans'. Hans told me that lowering a car with PASM is just fine as long as the force of the springs was within a margin of safety (he quoted some newton-meter figures but I forgot to write them down). He said THE most important thing is that the springs MUST be linear NOT progressive. He said progressive springs will ruin a PASM setup causing early failure of the struts. He has personally seen a tuner in Germany use progressive Boxster springs on a PASM Boxster and not only was the ride terrible when under loads, but one of the struts failed after a few thousand miles. If I recall his statements correctly, it had something to do with the valves in the PASM struts work in a linear fashion and when progressive springs are used the forces become to large too fast and the valves blow under the added stress. I asked him if he had a 'recommended' set of aftermarket springs for PASM to lower a PASM car and he said no, but that he knew several tuners were working on them. He was also of the opinion that a Cayman S with PASM does not need to be lowered to gain more performance and that lowering was more for look than functionality although with the right springs he would expect some performance improvement from lowering the center of gravity of the car. I know there are some members out there who have lowered their car with lowering springs that may not have been designed for the Cayman S , but I don't know if any of those cars had PASM or not. If you have a PASM car and have lowered using progressively wound springs (many lowering kits use progressive springs) then I would recommend swapping back to your factory springs until a linear set designed for PASM is available. Thanks to Hans (not his real name) for the excellent discussion, thoughtful insight and terrific advice which I wanted to pass on to our members.

K-Man S if we have non- PASM suspension can we lower the car for "looks" using the H& R springs supposedly designed for the Cayman ??

Well, I'm not sure I understand why a progressive setup would effect PASM in any way? It must be due to physical loads, not necessarily just because its dampening in a progressive fashion? Hmm... However, it would take a DOE to determine if it is in fact the truth. I'm sure Hans is closer to this than others as he is on the suspension team. Typically, aftermarket companies use progressive springs because they help to add firmness under load where the standard linear manufacturer springs don't (body roll / sway not ameliorated via progressive spring dampening). This is also why I never screw with the factory suspension setup. Changing camber for track day is one thing, but there's a reason Porsche put over 1 million miles on their Cayman mules....I tend to trust their judgement. Paul

In Europe a factory sport suspension with 20mm lowering is available for the 997 and rumors are that such a set up would be very easy for Porsche to offer on the Cayman if it chose to. The 986 Boxster had a Rest of World 030 sport suspension that was not offically available in the US. While Porsche certainly tunes their suspensions well, what is offered to us in the US by PCNA and Porsche AG often reflects marketing and DOT concerns rather than performance.

Devo, If I understand progressive springs correctly, near the end of the travel the springs get progressively stiffer because there is overall less distance to travel to achieve the same effect. For example if springs were 10' tall there would be 10' of distance over which to compress, but if you put 8' springs on to drop the car 2', then the last couple of inches are generally progressive to try and make up for the missing length correct? I'm not a suspension expert but I think he said it had to do with exceeding the valve limits during short burts and these burts blow out the valves after awhile. Has anyone checked the new GT3 ? It has PASM as I recall, are the springs progressive or linear?

Linear springs provide a constant spring rate across the entire compression (ie: K is a fixed constant) travel. A progressive spring will provide a higher spring rate (ie: higher K value) the more you compress the spring. So, a typical linear spring would be: 600 lb / in - or 600 lbs to compress the spring 1 inch. it will be 600 if its compressed 1 inch or 5 inches. a typical progressive spring: 450 - 700 lb / in. or 450 lbs to compress 1 inch, then under full load, 700 lb to compress the final 1 inch. So, at 1 inch of compression it is 450 lbs but at 5 inches of compression it takes 700 lbs to compress it one inch. Hope that makes sense. Paul

Funny you should mention that. I just read the August Excellence review of the GT3 which notes that the springs were changed from progressive to linear in the rear. On page 64: 'Incidentally, the new GT3 uses linear-rate coil springs all around. The 2004 GT3 used linear springs up front and progressive springs at the rear, but Porsche says this is no longer necessary thanks to PASM's 'active' damping, which requires linear-rate coil springs anyway'.

Good find scopacetic, that jives with what I was told as well! I remembered the 2004 GT3 had a mix from watching one get changed out so that's good to know that PASM needs linear springs and the GT3 is no exception!

I called H&R today and spoke with Josh. He says that their sport spring for the Cayman is PASM compatible with no problems. he pointed out that they make the OEM spring for Porsche . He also said they are out of stock until about June 19. These springs lower the car by 1.4 inches in the front and 1.2 inches in the rear.

So i assume the H&R PASM springs are not progressive? Do they have seperate kits for PASM and non- PASM ?

If H&R has the same part # for the Boxster and the Cayman then they haven't really done their homework and I doubt their statement that they supply Porsche with these parts since Porsche has different part numbers for these springs, likewise different between PASM and non- PASM . I'm going to need more proof than the word of someone selling the item in this instance.

H&R part number for CaymanS is 54020 H&R part number for Boxster is 29168-1 I didn't ask if the CaymanS spring is linear or progressive. They do not offer different springs for PASM and non- PASM . I'm going to use them. if you see me parked on the side of the road with a wheel amiss...please stop and help. thanks.

Greg, What is their part # for the Boxster S ? (987 version). I would make sure the springs are linear if your car has PASM . If we see you buy the side of the road with wheels/struts amiss we'll be sure to stop, what we do after that depends... /fckeditor/editor/images/smiley/MWPX/tounge_smile.gif

H&R does not list a spring for the Boxster S on their web site.

I'm having the H&R spring set installed on my car as I type. Ordered it directly from the dealer, as they were pretty competitive with the pricing. The spring set will lower the car by 1.2' all around, and is supposed to be fully compatible with the PASM . I'll post pics and provide an update once I get the car back.

Looking forward to the report! Can't see anyone improving the ride and suspension setup, it reallyis superbfor the factory, but I'm sure you could make it much worse easily and blow a few $$$K

So how have the PASM cars with H& R springs been doing? I'm about to have them installed on my car...

Somebody had a PASM failure after installing lowering springs, it was in another thread, I don't recall off-hand which make springs though, I think it was H&R.

Yeah, that thread is here: http://www.planet-9.com/topic.asp?TOPIC_ID=4441&FORUM_ID=4&CAT_ID=1&Topic_Title=PASM+failure+with+lowering%3F&Forum_Title=Cayman+Tech I'm guessing the installer didn't properly reconnect the wires. I'm aware of several 911's with PASM and H&R springs and have really liked the setup. H&R says their springs are PASM compliant; I have no reason to not believe them since they are a very reputable company.

Have someone tried Bilstein ? ' lowering by some 25 – 30 millimeters TechArt offers sport springs, which also harmonize perfectly with the PASM suspension available from the factory. Alternatively they offer a tighter set up sport suspension that was developed in cooperation with Bilstein. ' http://www.worldcarfans.com/tuners.cfm/tunerid/7060321.001/country/gcf/Porsche/techart-porsche-cayman-s-engine-tuning astek

No, but I see they are selling the PSS9 system for Cayman S with and without PASM: http://www.gmgracing.com/porsche_suspension.shtml 'Call for price'. I haven't called. Personally, I'm not ready to be the first with any of the suspension mods, but love to hear the reports from those eager enough to be pioneers.

Does this mean that at a press of a button the car will drop 25 to 30 mm? or the car will ride 20-30 mm lower then normal and in addition to that PASM will drop it another 10mm?

Good question , anyone have any more info on this ?