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Discussion Starter #1
I just received my GT4 and traded in a 981S w/ X73 SS. When I was contemplating the trade, and learned that X73 was not an option on GT4, but that the PASM was a GT-specific setup in part derived from the GT3, my hope was that it might actually be more comfortable for road use in the soft setting, and even better for track in the sport setting.

I am still in break-in mode, so no track yet, but I am delighted that at least the first half of my wish is true. The GT4 is surprisingly smooth and comfortable on the road, in normal/soft PASM mode, compared to X73.

As for track, it remains to be seen for me. The X73 was rough on the potholed streets of MS, but on track was sublime. At my last track event I left guys in GTSs and 997 GT3s scratching their heads how they couldn't shake me in my street stock 981S. Street brakes, street tires, but the X73 was a secret weapon. Could I have used more power? Sure. More brakes? Stickier tires? You bet. But more suspension? Not really. X73 was like a race suspension on a street car, for better (track) and for worse (most of the streets I have to deal with).

Which leads me to the 2nd part. I know the GT4 suspension is a bespoke GT suspension, borrowed from GT3 up front and built from scratch in the rear, and the chassis is adjustable for height, camber, toe, plus the adjustable anti-sway bars, but can an adaptive, electronically adjustable PASM really outshine X73 on track? I sure hope so, but it's a mighty high bar. I'd love to hear from anyone who has driven an X73-equipped 981 and a GT4 on track and get your thoughts on how they compare.

As an aside, another pleasant surprise is that the GT4 actually seems easier to get in and out of. It's supposed to be 30mm lower than standard compared to 20mm lower for X73, so maybe it's the seats/seat positioning, who knows. But it doesn't feel quite as low as my 981S w/ X73.

Julius
 

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"I'd love to hear from anyone who has driven an X73-equipped 981 and a GT4 on track and get your thoughts on how they compare."

Had the same set up. My X73 was installed after I purchased my CS. Agreed, the X73 was very impressive. I traded my car with the X73 and almost new giro-disks and fresh pagid yellows. A GT4 literately dropped in my lap and I had no time to change out. Somebody is going to get a sweet set-up!

Will let you know mid September.
 

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On a related note, PCNA has a video where TPC racing walks you through all of the GT4 specific chassis mods. Great video.
 

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I had X73 on my 981 CS as well. My 1st track day is going to be Sep 19th so I can only relate to the same on road driving you are experiencing. From what I have read the fast Nurburgring lap time was done in normal mode.
 

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As an aside, another pleasant surprise is that the GT4 actually seems easier to get in and out of. It's supposed to be 30mm lower than standard compared to 20mm lower for X73, so maybe it's the seats/seat positioning, who knows. But it doesn't feel quite as low as my 981S w/ X73.

Julius
I'm going on 68 and though more nimble than most, getting into my X73 SS equipped Cayman is an interesting dance. Now, getting into a Cayman that is an ADDITIONAL 10 mm lower, a first blush, would seem to be even that much MORE difficult -- not easier. I think the only explanation is that the "smile" on your face with that sweet GT4 just masks the grimace (unless you are a quite nimble youngster!!!).http://www.planet-9.com/images/smilies/hilarious.gif

Enjoy...
 

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[...]but can an adaptive, electronically adjustable PASM really outshine X73 on track? I sure hope so, but it's a mighty high bar. I'd love to hear from anyone who has driven an X73-equipped 981 and a GT4 on track and get your thoughts on how they compare.
I tinkered with that question a lot. I am sure that as far as precise driving feel adaptive suspensions will never beat good passive suspensions. They will always feel like the car isn't quite following orders and road - which it isn't. There is somebody constantly adjusting the dampers. So what the car does has a third component, one you can't predict.

Now, I moved on to the second question, which is, is it still better for track times and safety? I have looked quite a bit into how BMW's first level adaptive suspension (nor ARS etc) works, and there could be quite a bit of potential in -for example- dealing with bumps inside high-speed curves. It could cut down on the hobbling and hence on how far out you drift because of the bump. It could help keeping the car from spending energy on suspension compression. There is a gyroscopic sensor in the car working with the adaptive suspension, and it has access to the steering wheel angle. It knows whether you are current doing a high speed curve, or hard breaking. It could use to stem against suspension compression.

The third question is then, how aggressive would the manufacturers tune the software to help with "faster". At least in the BMW world it seems like the adaptive suspension is meant to still provide an OK sports mode in a suspension primarily made for comfort. However, it is hard to separate out the factors in play. It is very hard to get accurate driving data on current BMWs because everything still owed by BMW (for test drives at the dealer or tracking driving on events) has the runflat tires which no serious enthusiasts leaves on. The M models do not and F80 M buyers are very excited about their adaptive suspension.

Personally I will not order adaptive suspension again until I collect more data to sort out those questions.
 

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I don't think it's fair to compare a different driver on X73 Cayman vs an older GT3 and conclude the passive suspension was the main reason being the secret weapon. The 981 has improved vastly over older cars. The 981 GTS Is just as quick around a track as a 996 GT3. You would really need to have passive versus active suspension setup by the same driver and same (or at least somewhat comparable) car to figure out whether the X73 was the source for faster lap times. I have never heard of a Cayman GTS clocking faster times than even a 991 911 non GT car when driven by the same competent driver regardless of options. There is absolutely no way a cayman would give a car like GT3 in the same generation a hard time if that car's driven by an equally good driver ... That would mean all the GT3s out there have an extra 5 seconds to shave around the 'Ring if a cayman could pass a GT3 around a local track just cuz of X73

Sorry to sound like a hater, but personally I have never felt that the X73 particularly great. From my limited knowledge and observations, the X73 suspension actually doesn't exactly improve lap times although most owners who spec'd X73 feel that is a secret weapon -- also, if the X73 truly has performance implications over the regular PASM, Porsche would have advertised it left right and center. The X73 makes you feel more focused over a regular non-GT PASM setup. I don't think Porsche would have kept the PASM as the only available setup on all the GT models if passive setup was deemed faster around a track. The X73 is more direct and often feel stiffer. Humans tend to have the illusion that stiffer suspension automatically yields faster lap times ... Yet, why do Porsche test drivers always leave their cars' PASM mode in Normal while clocking 'Ring times?

the PASM certainly can feel unnatural at times, especially the earlier versions. The 981.1 non-GT program has come a long way but could still use some improvement. I have never driven the GT4 so I couldn't comment. So far TPC is the only one in the market who has created an aftermarket program for the PASM setup. The last time I tried it on my 987.1 car, I felt it was a vast improvement as the system was more responsive and just got everything right.
 

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Discussion Starter #8
I don't think it's fair to compare a different driver on X73 Cayman vs an older GT3 and conclude the passive suspension was the main reason being the secret weapon. The 981 has improved vastly over older cars. The 981 GTS Is just as quick around a track as a 996 GT3. You would really need to have passive versus active suspension setup by the same driver and same (or at least somewhat comparable) car to figure out whether the X73 was the source for faster lap times. I have never heard of a Cayman GTS clocking faster times than even a 991 911 non GT car when driven by the same competent driver regardless of options. There is absolutely no way a cayman would give a car like GT3 in the same generation a hard time if that car's driven by an equally good driver ... That would mean all the GT3s out there have an extra 5 seconds to shave around the 'Ring if a cayman could pass a GT3 around a local track just cuz of X73

Sorry to sound like a hater, but personally I have never felt that the X73 particularly great. From my limited knowledge and observations, the X73 suspension actually doesn't exactly improve lap times although most owners who spec'd X73 feel that is a secret weapon -- also, if the X73 truly has performance implications over the regular PASM, Porsche would have advertised it left right and center. The X73 makes you feel more focused over a regular non-GT PASM setup. I don't think Porsche would have kept the PASM as the only available setup on all the GT models if passive setup was deemed faster around a track. The X73 is more direct and often feel stiffer. Humans tend to have the illusion that stiffer suspension automatically yields faster lap times ... Yet, why do Porsche test drivers always leave their cars' PASM mode in Normal while clocking 'Ring times?

the PASM certainly can feel unnatural at times, especially the earlier versions. The 981.1 non-GT program has come a long way but could still use some improvement. I have never driven the GT4 so I couldn't comment. So far TPC is the only one in the market who has created an aftermarket program for the PASM setup. The last time I tried it on my 987.1 car, I felt it was a vast improvement as the system was more responsive and just got everything right.
several testers recorded faster lap times in a GTS with X73 than in a GTS with PASM, the suspension being the only difference. The reason to promote PASM over X73 for Porsche is probably because it costs more, is more technologically advanced, and is the better choice for how most owners drive their cars.

i don't want to debate which is "better". I loved X73 but so far am very optimistic about GT4 PASM. But I have driven many cars, from street stock to fully race prepared on many circuits, and my own personal experience with X73 is that I couldn't have asked more of the suspension on track, and I've never felt that way in a street car. In most street cars the suspension would be the weakest link, the first thing to upgrade to improve track performance. Not so with X73. As I said, I believe I could've used more power, better brakes, stickier tires, but the suspension did its job beautifully with little need for improvement. I just hope to be able to say the same for the GT4 PASM setup. I'm not at al, suggesting that I expect to be disappointed. To the contrary.
 

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several testers recorded faster lap times in a GTS with X73 than in a GTS with PASM, the suspension being the only difference. The reason to promote PASM over X73 for Porsche is probably because it costs more, is more technologically advanced, and is the better choice for how most owners drive their cars.

i don't want to debate which is "better". I loved X73 but so far am very optimistic about GT4 PASM. But I have driven many cars, from street stock to fully race prepared on many circuits, and my own personal experience with X73 is that I couldn't have asked more of the suspension on track, and I've never felt that way in a street car. In most street cars the suspension would be the weakest link, the first thing to upgrade to improve track performance. Not so with X73. As I said, I believe I could've used more power, better brakes, stickier tires, but the suspension did its job beautifully with little need for improvement. I just hope to be able to say the same for the GT4 PASM setup. I'm not at al, suggesting that I expect to be disappointed. To the contrary.
not here to challenge you or anything. But could you quote the testers with results? Very curious about this, especially when the GT cars give you nothing else but PASM. I would be very interested to see why PAG slapped on PASM setup over passive setup if the PASM setup is significantly inferior to passive setup in performance. Clearly the PASM is there partly for comfort. But I'm really curious if the passive setup would be able to offer a sharp increase in performance over active. I can't imagine PAG putting PASM on every possible GT car when a passive setup would shave you seconds off a lap to bring a car equipped with passive setup. Why not passive GT3 and PASM GT4 just to mess with everyone?

i honestly have never ever seen a proper comparison between sport suspension vs PASM done by an unbiased yet competent driver. All the comments I have heard so far are done by drivers who own and are extremely familiar with the X73 cars but not PASM cars. So ya ... I'm really curious who has ever done an unbiased test with a high level of consistently and competency. Guys who own x73 cars with extensive track expletive operating a PASM car for 5 mins wouldn't really count as a fair comparison. I would be utterly shocked if PAG keeps the PASM system in all their GT cars just so that they could collect an extra 500 USD or so of money on their regular road cars.
 

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Discussion Starter #10
not here to challenge you or anything. But could you quote the testers with results? Very curious about this, especially when the GT cars give you nothing else but PASM. I would be very interested to see why PAG slapped on PASM setup over passive setup if the PASM setup is significantly inferior to passive setup in performance. Clearly the PASM is there partly for comfort. But I'm really curious if the passive setup would be able to offer a sharp increase in performance over passive
I'll try to find the reviews I referred to, but I want to clarify that I'm not saying passive is inherently better than active. I'm saying the X73 passive setup was a better track option, a more sporting setup, than the PASM setup available on on the Cayman S or GTS. Not necessarily because it was passive. Keep in mind the PASM on the GT4 is completely different from the PASM on S or GTS. I'm sure PASM can be tuned to meet or exceed a passive setup, but of the three suspension options available on S, PASM was positioned between stock and X73 in terms of sporting intent. On the GT4, I believe/assume/hope that PASM is tuned to exceed the track performance that X73 would deliver. That is the only reason that makes sense to me that X73 would've been available as an option on GTS and not GT4.
 

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I sold my 15CS X73 and it was a very good. I also had a 14CS with PASM. On the X73 I maxed out the f neg and set it up. I tracked it and it was very good on smooth tracks,a little skittish on a bumpy tracks like turn [email protected] The gt4 is about the same stiffness as the X73 but not as harsh, the dampening is much better. The main you feel is the spherical bearings in the control arms and how much quicker it responds to steering inputs and the overall stiffer chassis. The other day i went to my dealer and took a X73 out to my handling course to compare back to back. Overall the GT4 suspension by far the best out of the box set up Ive ever had. Including a 996GT3,996GT2,993TT.981X73&pasm,Lotus exigeS,TTRS ect. carl
 

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There are two main issues that need to be tackled separately: spring rates and shocks.

Spring rates for the GT4 are up 50% in front and 70% in the rear vs the X73, while swaybars are also stiffer. This gives the GT4 significantly better platform control that the X73- at a given cornering G force it's going to roll less than 2/3 as much. On the other hand this also means the GT4 gets more upset by bumps. As most tracks are smoother and you're pulling high cornering Gs these stiff springs will significantly benefit the GT4 on track.

Shocks tuned to control these springs are a separate issue. PASM is responsible for the GT4's great ride over over smaller bumps and broken pavement, because it's digital and thus has a far wider dynamic range than the analog Z73. However PASM can only react, not predict, and by definition it doesn't react consistently. Sometimes it gets confused by the wrong patch of pavement, at which point the GT4 gets bouncy and feels underdamped. This is the exception, but it occasionally surprises, leaving me wondering exactly how it's going to react next time. X73 shocks give a relatively harsh ride given the lower spring rates, but they are totally consistent and transparent in operation, and hence more confidence inspiring.

PASM tries to give the best of both worlds- great ride and race car handling simultaneously. It does that admirably. The best analog shocks on the other hand are specialists- they focus on doing one thing well. If they are tuned for what you want them for they are more consistent, and arguably still superior to PASM at that one thing. Hence the selection of X73 for the Boxster Spyder.

The X73 package is tuned not for the track, but for fast street. I prefer it to the GT4's PASM system in that roll. On track I expect the GT4 to be significantly superior overall- I autocross the car tomorrow so I'll get a bit more insight. For a pure track car I'd rather it wasn't PASM, but a stiffer analog system. For a daily driver, weekend car plus track car the PASM is probably the best compromise available. For just a weekend car and track car I'd give up some comfort and take stiffer analog shocks- these would make the ride harsher, but also give the car a little more sensory feedback when going slowly. The car also seems under-damped for low speed/ autocross, and I suspect analog shocks would improve that as well.
 

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Wake me up when I can put my own software for the adaptive suspensions :)

I guess BMWs are a bit closer to having a rootkit than Porsches, though.
 

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The PASM is there partly for comfort and partly for grip. Road cars often get stuck in situations where road conditions are so bad that the car ends up losing grip at higher speeds -- this applies to even some of the race tracks. There is no doubt these comparable (i.e. in generation) GT-cars would out handle an X73 as there is a lot more going on than just springs and shocks. I think anyone who really thinks bone stock 981 X73 is even anywhere close to bone stock GT4 when driven by a competent driver must be imagining things 24/7 -- but I know no one here thinks so.

The discussion is whether PASM vs X73 on the same car would even yield a significant performance difference. The X73 would give the driver a more raw and exciting experience, while the PASM would give the driver a bit more comfort and a more versatile car for various road conditions. Although it's by no means an official race, my friend and I went through some very challenging winding roads. I was on a PASM equipped car while he was on X73. His car had a lot of trouble getting through a few turns without feeling the rear was skipping around, while my car was able to struggle through all that with a PASM. Grip is actually another reason for PASM (as well as other active suspension out there in Ferrari etc) which some tend to overlook.

In some ways, the "sport" mode in a regular non-GT4 981 PASM is actually pretty much an X73 except the damping rates are even higher. From my understanding (and I could be wrong), PASM in Normal mode opens the valves at default positions while Sport model closes the valves at default positions. This means that the Normal mode acts much more like soft dampers that stiffen up when needed, while Sport mode is stiff dampers that soften up when needed. On top of that the algorithm and tolerances are also very different. That's why between the PASM system's program itself, along with the two available modes, the PASM setup could tackle a lot of conditions at the expense of feeling unnatural. Most feel that the X73 is "faster" merely because it inspires more confidence for drivers not familiar with active suspensions, and it's natural human tendency to think that stiffer suspension + more raw = faster. That's why people never get tired of driving cars like older Hondas even though they aren't the fastest cars out there.

As I really do believe, PAG wouldn't have put in PASM into all their GT cars if the concept of active suspension is proven to be substantially inferior to the passive system in performance. I'm not saying all GT-cars are 100% performance oriented and are race cars, but any significant draw back would be considered seriously. On top of that ... it does appear that most if not all the timed laps with extremely impressive results around the Ring were timed with PASM under Normal mode, which actually is "softer" on average than an otherwise proposed passive setup. Also, the PASM programs on older GT cars were very similar in mapping compared to non-GT cars. I'm not sure whether 981/991 GT cars are same as I haven't driven them to be able to compare. But for 997 cars, the diff between GT3 and non-GT3 PASM program isn't as big as others think.
 

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On top of that ... it does appear that most if not all the timed laps with extremely impressive results around the Ring were timed with PASM under Normal mode, which actually is "softer" on average than an otherwise proposed passive setup.
I am not surprised by this, as "road rally" cars often have thinner anti-roll bars and lower spring rates relative to track cars. A lower spring rate ensures maximum contact between the tire and road surface particularly on bumpy roads - resulting in maximum traction and grip (assuming a well damped vehicle). Likewise for the anti-roll bars - a thin bar promotes the full use of the contact patch whereas a thicker bar results in force distribution towards the outer edge of the wheel/tire combo leading to more readily attainable oversteer (or worse still uncontollable snap oversteer :))
 

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IMO Porsche is trying to give the maximum off both worlds ( street/track ) but falling sort of the greatest of each. After all many GT cars are bought with the intent of not being tracked and Porsche knows this. You put in a suspension stiffer than X73 and see your GT car sales take a dump. An owner who tracks his GT car twice a year surly does not want to have to deal with a hardcore suspension the other 363 days of the year on the street.

Lap times matter in Real Races with Real Racecars.....$$$ matters in the real world with track cars for fun.
 

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PASM can tune the shocks to the road. As with adjustable passive dampers this does offer theoretical advantages as roads change. If these outweigh the disadvantages of consistency or not will depend on the road. As I said, PASM offers more breadth of ability, but less depth- it doesn't do the one thing quite as well.

An ideal suspension would adjust spring rate as the road changes, then tune the shocks to match. The advantage of a stiffer car is that it doesn't lean as much in corners and reacts faster, but stiffer gives up grip over bumps. Sport PASM can "fake" a stiffer car by over-damping the chassis, improving transient response. However in a steady state corner the shocks don't prevent the car leaning over, while the over-damped springs more than a properly damped spring/ shock combo. Hence it's not as good as a spring-rate bump, but it's better than nothing.

A stiffer car is harder to drive- less consistent grip requires more corrections. Yet ultimately racers generally like stiffer, preferring the extra response and sorting the car out themselves. Hence a GT3 Cup car is many times stiffer than a GT3 road car, while an RSR is twice as stiff again, even if they run on bumpy tracks like the 'Ring.

Regular PASM "fakes" stiffer by bumping the shock rates. X73 actually gives the car stiffer springs with ideally matched shocks. GT4 PASM bumps spring rates even further, then fakes even stiffer with more damping in sport. Which is best for performance will depend on the road and the driver. The GT4 units are excellent on course, but do give up something on many roads to the X73. Meanwhile the standard 918 PASM units attempt to improved chassis control falls short of X73 for me, both in consistency and because the shocks and springs are imperfectly matched depending on setting. The best, most transparent PASM I've tried is in the RS 4.0. I'm convinced this is because PASM does very little in that car- in the RS 3.8 you can feel a big difference between the settings, in the 4.0 it seems smaller.

I suspect the other big variable here is the quality of the GT4's shocks. These are clearly more expensive units than the X73: upside down, stiffer in bending and almost certainly lower friction. The ride reminds me of Öhlins or similar race shocks, very low stiction...

Back to the original question, after autocrossing yesterday I'm convinced the GT4 suspension is significantly better on track than X73, at least in feel. I'd probably leave it in "soft" mode at first, as I believe "sport" does overdamp the car somwhat.
 

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Are the anti-roll bars the same with x73 and PASM?
 

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Nope, ~10% stiffer front, 30% stiffer rear with X73.
 
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