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    PASM and damptronics

     I have been reading the threads on improving the turbos handling with much interest and thought it would be educational to have a look at the theory side of it. I am not a physics expert or a suspension specialist. I am setting down my thoughts in the hope that those with better knowledge than me will either affirm or correct my logic.  So, firstly springs, what are their purpose(s)? 1. to absorb the forces attempting to unsettle the car when a wheel hits a bump. A softer spring gives a more compliant ride and returns the wheel to the road quickly after passing over the bump. 2. To reduce the transfer of weight to the outside of the wheels during cornering in order to increase total grip. Stiffer springs = less weight transfer = more cornering grip. 3. To reduce transfer of weight to the front wheels during breaking to increase grip for maximum breaking. Stiffer springs = better breaking. 4. To reduce transfer of weight to rear wheels during acceleration (squatting) giving better acceleration for 4 wheel drive cars. Stiffer springs bring improvement for 4 wheel drive. Maybe not true for 2 wheel drive. Now Dampers: Dampers have a much simpler job of preventing the oscillation that is a characteristic of springs. Their aim is to allow a spring to contract under load then return to its neutral state without continuing past the neutral state.   To further differentiate between the two, a spring provides a continuing opposing force to a force acting on a wheel whereas a damper provides a momentary initial opposing force that reduces over time. Now here is the big one: The damper should be set according to the stiffness of the spring and the load on the spring. There is one perfect setting for the damper to exactly control the compression and decompression of the spring. When this is set right, the contact between tyres and road will be maximised. There is not a best setting for track and a best setting for road use. Agree? If it were possible, the adjustable component should be the spring. The damper would then need adjusting but only to match the spring. Since adjustable springs don't exist (?) they have created adjustable dampers. The damper can then do some of the job that should really be done by the spring. Ie PASM in sport mode. The result is less compliance over bumps and anti roll resistance that reduces through the corner as the damper contracts and passes the job of resisting body roll over to the spring. So PASM in sport mode improves initial turn in but does not help prevent body roll. I am ignoring anti roll bars deliberately. PASM in sport mode is a compromise to attempt to create some improved handling but it will be less effective than stiffer springs with well matched dampers and less compliant too. When the damper has too much resistance it does not let the spring rebound fast enough to keep the tyre in contact with the road after hitting a bump. I assume that the damper compression resistance is the same as the damper decompression resistance(?)  So if the perfect damper setting for soft spring is 3 on a scale of 1 to 10, I would guess that PASM is using 3 for normal mode and 8 for sport mode(?) ie it appears to be optimised for normal mode rather than sport mode. If damptronics is configurable you could choose to have sport mode as the one that best matches the stiffer spring, and have nomal mode as the compromise setting(?) ie optimised for sport mode rather than normal mode. If all this is somewhere near the truth, maybe the most important decision for an upgrade is the spring rather than the damper?
    --

    Paul

    996 GT3 RS

    997.2 C2S Cab

    How to Save Money


    Re: PASM and damptronics

    The damper is responsible for absorbing the shocks from the road, while the spring is responsible for pushing the wheel back to it's normal riding position and carrying the weight of the car.

    Stiffer springs do indeed reduce the body roll, but the weight transfer of the car remains almost the same during braking/accelerating/cornering (although you cannot see it). 

    The weight transfer is heavily depending on the center of mass of the car and therefore the ride height. If you reduce the ride height, you have to stiffen the springs to prevent the car from hitting the ground.

    If you are going for grip, softer springs are better, especially on rougher surfaces, as the spring will push the tire down more and therefore give you grip where the tire would not even be in contact with the road with stiff springs. Rally cars have much softer springs compared to track cars.

    Springs however, have the tendency to swing, which can have awful effects. The damper is there to prevent that and therefore damper, spring and ride height have to be seen together as a unit


    Re: PASM and damptronics

    Using your scale, I was told that PASM in Normal mode tries to stay on 1 but moves to 7/8 when required whereas in Sport mode, it tries to stay on 10 and moves to 7/6 when required.  Standard steel springs are set on 7.  What has always perplexed me with PASM is that I was taught to match springs and dampers based on the unsprung and sprung mass.  So how are variable dampers so succesful?  I guess first year undergraduate theory is miles away from the real world.

    Eunice is spot on but its also worth noting that dampers dissipate energy and respond to velocity inputs, wheras springs store energy and respond to displacement inputs.  So in a highly dynamic environment (i.e. fast weight transfer), the damper stiffness has a very big effect .  Then you have to factor in the anti-roll bars which are a great big torsion spring!


    Re: PASM and damptronics

    Sorry that my previous post was all merged into one paragraph. It did not look like that when I pasted it into the page. Eunice, thanks for mentioning the ride height and that dampers are shock absorbers. I can see this is a major factor in reducing body roll on the corners. My understanding of why body roll is bad is that it reduces the contact pressure between the inner tyres and the road and therefore reduces grip. But, on a smooth track, surely stiffer springs are better to help reduce weight transfer when cornering (as well as preventing the car underside from grounding). Stiffer springs will also help 'turn in' yes? GR, as you say the anti roll bars are there for this reason too. It would be nice to incrementally upgrade the suspension components and alter their characteristics but as stated they should be treated as one. I imagine this would include tyres and the wheel settings (camber and toe in) too. For example, a set up with softer springs would require more negative camber than one with stiffer springs. It's a complicated subject isn't it. I can see why some companies have their secrets.
    --

    Paul

    996 GT3 RS

    997.2 C2S Cab

    How to Save Money


    Re: PASM and damptronics

    @Pink Panther: yup Paragraphs are nice


    --

    Rennteam Moderator - 997.1 C2S Coupe GT Silver/Cocoa, -20mm/LSD, PSE, SportDesign rims, Zuffenhausen collection


    Re: PASM and damptronics

    Pink Panther:
     .... I assume that the damper compression resistance is the same as the damper decompression resistance(?) 

    Fascinating topic and you drew me out of temporary rennteam retirement while preparing for summer trip(s) for my family. Smiley
    First the warning: I am a complete amateur and what I write is therefore amateurish interpretation of what the pro's told me, or what I've read. In other words, I could be wrong.

    The answer to the above is no, compression and rebound dampening forces (I assume this is what you meant by resistance) are not the same. The compression force is usually LESS than the rebound force.

    There is an explanation for this that I've read about but don't remember anymore, and am not sure my limited knowledge allows me to understand the concept fully. I VAGUELY recall that it has something to do with the weight of the car:
    During compression, the weight of the car is working against the compression force. That is, the bump on the road is compressing the coilover with the weight of the car on top of it.
    During rebound, the wheel is moving out, without weight of car being a hindrance.
    Bottom line: I am NOT sure that this explanation is valid; it seems to make some sense some time, but when I think more about it, some time it doesn't. Regardless of what the explanation is, it is true that the forces are not the same, as illustrated by the following Bilstein curve that belongs to the Bilstein B16 PSS10 (the curves are the 10 settings of the coilover, changeable by a knob at one end of the coilover). Note that the rebound forces are numerically higher than compression forces.1248302460526bilsteinPSS10curvessharpen label 1.jpg


    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

    ^^^^^ About the red markings called low speed, medium, and high speed (for anyone who don't already know): They are unrelated to the question but IMHO are critically important in any discussion of dampening effect. A very subtle point that took me a long time to understand, or think I understand (my amateurish questions MUST have driven the guys at USA Bilstein crazy!).

    The speed is NOT the car's speed (many amateurs, including me, were at one point or another confused by this), but that of the shaft of the coilover, or "shaft velocity":

    1. High speed: This is what happens when, for example, you hit a bump on the road. The coilover shaft compresses, quickly.

    2. Low speed: This is what happens when you are rounding the curves and enter corners, or when you brake. The car leans, causing the coilover shaft to compress, but not at nearly the same speed as in 1 above.

    The way I look at it, 1 has to do with comfort and wheel contact when you hit a bump. 2 has to do with the car's dynamics (side to side leaning, front to back leaning) during braking and while entering corners.
    When I "discovered" this distinction, I was much fascinated by the 2 entirely different facets of what coilovers "do."

    In more "serious" coilovers (Moton, Bilstein high-end stuffs), these adjustments are independently adjustable: low speed compression, high speed compression, low speed rebound, high speed rebound, etc. In the B16 that most of us use for the Turbo, none of these is adjustable. In many ways, a blessing.


    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

    I just made a post that didn't appear so hopefully this will be ok The paragraphs are not working because I am posting from an iPhone while touring Canadian Rockies. I post was written to point out that unsprung masses are probably important part of getting the damper settings right to. Saving weight with pccb and lighter wheels would mean the spring and damper have less to deal with and therefore require less resistance(?) Can, Thanks for the insightful comments and graph.
    --

    Paul

    996 GT3 RS

    997.2 C2S Cab

    How to Save Money


    Re: PASM and damptronics

     Thanks cannga, for these insightful posts. Of course the unsprung mass is a vital part of the equation.

    What I'ld like to know is, if the weight transfer really changes due to softer springs and more body roll. I think with stiffer springs the weight is still transferred, it just doesn't result in body roll.


    Re: PASM and damptronics

    Good question. In order to answer it I think it helpful to exaggerate what is going on. Imagine a double decker bus with high centre of gravity going round a corner. If it had soft springs it would lean away from the turn and the centre of gravity would move over the outside wheels. On firm springs this would happen less. The same is true in a car but less obvious to the eye. This is why lowering the centre of gravity is important. The aim is to use all four tyres as effectively as possible through the corner. Hope that helps.
    --

    Paul

    996 GT3 RS

    997.2 C2S Cab

    How to Save Money


    Re: PASM and damptronics

    Pink Panther:
    So, firstly springs, what are their purpose(s)? 1. to absorb the forces attempting to unsettle the car when a wheel hits a bump. A softer spring gives a more compliant ride and returns the wheel to the road quickly after passing over the bump. 2. To reduce the transfer of weight to the outside of the wheels during cornering in order to increase total grip. Stiffer springs = less weight transfer = more cornering grip.

    Hey Paul, thanks and glad you find the discussion interesting. (If you typed that whole paragraph out of an iphone, then now I must consider getting one for myself! Smiley Very impressive.) 
    I didn't have time last night but your brought up another interesting point (highlighted) that brings to mind a similar discussion we had in that Bilstein thread here. The discussion at that time, joined by the Editor of a US Porsche Mag (Excellence): Is stiffer always better in corner? The answer, not surprising at all in a topic as complicated as this,  is, up to a certain point yes, but not necessarily always, and, it depends... Smiley

    It seems to me cornering behavior of the car must take into account 2 different parameters, both influenced by the choice of spring rate. A stiffer spring helps one parameter, but may "hurt" the other. The 2 are:
    1. Chassis control -- or how the suspension reduces side to side leaning.
    2. Tire adhesion.
    While a stiffer spring helps with chassis control (less leaning) and undoubtedly results in better "handling," a stiffly sprung car also likes to go airborne, therefore losing traction more easily, especially if road surface is not smooth. These 2 aspects therefore must be balanced against one another to achieve the fastest speed that a car could take corners. The issue is more important on the streets (versus track), when road surface is almost never perfect.

    I believe the following article discusses a similar point. It may not be authoritative and I might be quoting them out of context, but regardless, it's a very interesting read.
    http://www.f1technical.net/articles/39
    ...
    The springs or torsion bars are the parts of the suspension that actually absorb the bumps. In simple terms, the softer the suspension on the car, the quicker it will travel through a corner. This has the adverse effect of making the car less sensitive to the drivers input, causing sloppy handling. A harder sprung car will have less mechanical grip through the corner, but the handling will be more sensitive and more direct, ideal for circuits such as Monaco where the drivers must be inch perfect between the barriers.
    ...


    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

    Eunice:

     .....

    What I'ld like to know is, if the weight transfer really changes due to softer springs and more body roll. I think with stiffer springs the weight is still transferred, it just doesn't result in body roll.

    Eunice, thanks. I have nothing to add re. weight transfer, but that same article I quoted above has a little discussion on that as well. I do find the last sentence (highlighted) very interesting.

    >>>>>>>>>>>>>>>>
    Weight transfer is the general term for most forces a car undergoes in any change of condition. It is a shifting of loading on the four outmost corners of the car. Acceleration means load is transferred to the back of the car, the opposite occurs when braking. In corners, most weight becomes lying in the two outside wheels. These kinds of weight transfer can be expressed and calculated with the following formula:

    blah blah blah (incomprehensible letters) Smiley

    Different types of weight transfer:

    • Heave is the motion of the chassis when all four wheels go up or down in unison i.e. when a car drives through Aux Rouges at Spa, that car is pushed down onto the track, due to the surface which is basically a narrow valley. When thus driving over a hill, the opposite occurs and the car wants to fly away.
    • Pitch is when the front and rear of the chassis go in opposite directions, either up or down. This occurs at braking when the car seemingly bends forward, or accelerating so that the car want to raise its nose.
    • Roll is a side-to-side movement of the car. The suspension on the outer side of the car compresses while the inner suspension extends. This occurs during cornering.
    • Warp is the movement of the diagonally opposed wheels in opposite directions i.e. the front left suspension compresses as the right rear extends.
    • Yaw is the rotation of the car in a horizontal plane around a vertical axis. This occurs during cornering.

    Weight transfer has to be absorbed or taken up by the suspension system, otherwise it will be expended at the tire contact patch meaning a loss of adhesion and a spin-out.


    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

    Great cannga, thank you very much.

    Coming back to the extreme example of the cornering bus: With stiffer springs, it almost immediately has two wheels airborne, therefore loosing grip in the corner.

    With softer spring, the tires stay in contact with the road and the grip is maintained.

    However, the softer springs come with more body roll, which slows down wheight transfer from left to right.

    20 years ago, race cars usually had very soft springs, and the driver had to think two corners ahead. 


    Re: PASM and damptronics

    Thanks Can, some good reading material there. The iPhone is not good for text input. It was a labour of love. Current hotel has WiFi - Yey!!!

    Eunice, thanks for correcting me. I can see you are right but I cant get my head around it yet.

    Now I am puzzled about why more extreme road going cars have firmer suspension eg GT2

    Glad I started this thread as I am learning a lot.


    --

    Paul

    996 GT3 RS

    997.2 C2S Cab

    How to Save Money


    Re: PASM and damptronics

    Pink Panther:

    Now I am puzzled about why more extreme road going cars have firmer suspension eg GT2

    Glad I started this thread as I am learning a lot.

     Yea, I'm learning a lot too.

    I think the ride height is the key, it is MUCH lower than in early day race cars, resulting in a lower gravity center and better cornering due to the improved weight distribution.  

    To lower the ride height you need stiffer springs, with the added benefit of faster change of direction (like in an "S" curve) and more direct handling (turning the steering wheel first compresses the springs and then leads to a change of direction).

    In the early days of racing, dampers where not as good as today, so maybe that's why they needed softer springs to reduce shaking of the car.

    But that's only guessing, Cannga, please help us out once again: Why do newer cars have stiffer springs? 


    Re: PASM and damptronics

    Pink Panther:

    Now I am puzzled about why more extreme road going cars have firmer suspension eg GT2

     

    Paul,

    First, I should add that I love your current garage (996 GT3 RS and 997.2). The 997.2 has PDK?
    If I ever add a second Porsche, it would be a 996 GT3, or better yet 996 GT3 RS, and 997.2 GT3 if I win the lottery (hope they have solved the RMS problem, that for some strange reason, seems to be a lot more common in 997.1 GT3 than 996 GT3).

    Second, once again noting my amateur status, IMO, extreme road going car is stiffer, because a stiffer car IS a better handling car, assuming the following conditions:
    1. Ride comfort is not the number one priority. As in a car designed mainly for the track.
    2. Road surface is smooth AND does not have too many peaks (stiffer cars is more likely to be airborne) and valleys. As in a track.

    At any given time, a car's suspension setup has to balance 1 & 2 above versus 3, which is,
    3. A stiffer car in general will have better handling.

    In other words, I did not mean to say stiffer is not better, but stiffer is not ALWAYS better. I have very little doubt those open wheel race cars for the US track ovals have bone-jarring stiff suspension.

    BTW, I have driven a 997 GT2 and I actually don't think it's that stiff; it's truly an outstanding road/track compromise and deserves the title of best 911 suspension ever, perhaps until 997.2 GT3. The drive in the GT2 was a major reason why I almost sold my Turbo, prior to installing the Bilstein.


    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

    Hi Can,

    My C2S is manual. I haven't bonded with the car like I have with other Porsches. It seems to have lost the x factor that was present in Gen 1 Carreras. Having read about your's and Alex's improvements to the Turbo I have found a turbo that I will swap my cab for. A GT Silver/Cocoa manual with bucket seats. Unfortunately not PCCB. There was a turbo with PCCB in slate which looked stunning but sadly it was tiptronic. So I am thinking through various upgrades:

    1. PCCB - costs a lot of money but possibly worth it for the reduced unsprung mass. Need to research cheaper parts suppliers.

    2. Exhaust - not researched yet but cargraphic sounds like a strong contender

    3. Lighter wheels with Michelin PS2

    4 a. Stiffer springs and Bilstein dampers

       b. Adjustments to toe in and camber

       c. Sway bars

    5. Tuning - might not bother with this or save it for a later date.

    I think it makes sense to do the weight loss mods first as they will effect the spring and damper settings. I hope to take up Alex's offer of a ride in his turbo prior tomaking any decisions.

    The turbo will be used as a long distance tourer so I need to be conservative on changes to suspension for my wife's sake. If she finds it too firm then it won't be fit for purpose.

    My 996 GT3 RS is a keeper although she is currently being repaired after I spun her off the track.


    --

    Paul

    996 GT3 RS

    997.2 C2S Cab

    How to Save Money


    Re: PASM and damptronics

    Eunice:

    Coming back to the extreme example of the cornering bus: With stiffer springs, it almost immediately has two wheels airborne, therefore loosing grip in the corner.

    With softer spring, the tires stay in contact with the road and the grip is maintained.

    However, the softer springs come with more body roll, which slows down wheight transfer from left to right.

     

    Yes, we are on the same channel! The realization that stiffer suspension may actually be SLOWER in certain road conditions (peak/valley and imperfect surface) was an a-ha moment for me when I was a complete novice to this and was looking for way to improve the Turbo's suspension.

    In retrospect, it is such an obvious concept. But...  I am sure I am NOT the only amateur who has been confused by the give and take of this aspect of suspension setup.

    As far as your question about whether "newer" cars have stiffer springs: I can't comment on the 993, but for 996 and 997, I do not believe this is the case.
    With respect to 996 and 997 GT3 and Turbo for example, I have reasons to believe that there was NO significant change in spring rates between the 996's and 997's. The 996 spring rates are known -- in my Bilstein thread, first page, but those for 997 have remained a mystery. That said, as mentioned I do not believe there was a drastic change.

    For the Turbo, both 996 and 997 Turbo are disappointingly soft car. I know the cars were tested and approved by WR (LOL, I have to use abbreviation since I always have trouble with spelling his last name, Rorhl, Rohrl, or Rolhr, or Rorlh? Smiley), I still say they are way too soft for a flagship sports car. And I am not the only one whining -- WR is the king but he still has to follow PAG's marketing decision with respect to the Turbo's suspension.

    For the GT3, going by what others have told me and what I've read between the lines (I have no direct experience): The difference between 996 and 997 GT3 is that, speculating here, on the track they are similar, but on the street the 996 is much tougher on passengers. So if anything, the 997 *might* be the overall "softer" feeling car.

    BTW, suspension is such a complicated topic but I think it's so much fun for us amateurs to try to understand. It's by far my favorite thing to read about. I've run into even more complicated articles where I could only shake my head and give up. For example check this one out:
    http://www.rqriley.com/suspensn.htm
    The ride quality normally associated with the vehicle's response to bumps is a factor of the relatively low frequency bounce and rebound movements of the suspension system. Following a bump, the undamped suspension (without shocks) of a vehicle will experience a series of oscillations that will cycle according to the natural frequency of the system. Ride is perceived as most comfortable when the natural frequency is in the range of 60 to 90 cycles per minute (CPM), or about 1 Hz to 1.5 Hz. When the frequency approaches 120 CPM (2 Hz), occupants perceive the ride as harsh. Smiley Smiley Smiley Consequently, the suspension of the average family sedan will have a natural frequency of about 60 to 90 CPM.  Smiley Smiley Smiley A high-performance sports car will have a stiffer suspension with a natural frequency of about 120 to 150 CPM (2 to 2.5 Hz).


    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

     Wow, thanks canna.

    Just for your info, it is Röhrl. If there's no possibility to write the umlaut "ö", a German would write Roehrl instead.


    Re: PASM and damptronics

    I might be converting to motons soon as i heard that you can in 2 mins change from a setting that is softer than even damptronics for town and commuting while a few clicks later have a true track suspension (with same springs). The damptronics are truely better than stock bilsteins but still low in the food chain of suspensions. (ie still not good enough for track use).

    I will report findings when i try them.


    Re: PASM and damptronics

    Pink Panther:
    My understanding of why body roll is bad is that it reduces the contact pressure between the inner tyres and the road and therefore reduces grip. But, on a smooth track, surely stiffer springs are better to help reduce weight transfer when cornering (as well as preventing the car underside from grounding).

    What has been left out of the equation so far is the importance of the tire itself. The correlation of applying force and grip is not linear, so the amount of force on one single wheel, usually the front outer wheel during cornering, should be kept as low as possible.


    Re: PASM and damptronics

    Ferdie:
    Pink Panther:
    My understanding of why body roll is bad is that it reduces the contact pressure between the inner tyres and the road and therefore reduces grip. But, on a smooth track, surely stiffer springs are better to help reduce weight transfer when cornering (as well as preventing the car underside from grounding).

    What has been left out of the equation so far is the importance of the tire itself. The correlation of applying force and grip is not linear, so the amount of force on one single wheel, usually the front outer wheel during cornering, should be kept as low as possible.

    Good point. Discussion getting more interesting!


    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics


    Pink Panther:
    My understanding of why body roll is bad is that it reduces the contact pressure between the inner tyres and the road and therefore reduces grip. But, on a smooth track, surely stiffer springs are better to help reduce weight transfer when cornering (as well as preventing the car underside from grounding).

     

    Very much agreed. There are 2 separate situations that I did not make distinct:

    1. On a smooth surface: As you discussed above, stiffer is better because a stiffer suspension reduces weight transfer, hence causes less leaning, and hence maintains tire contact patch of the inside wheels better.

    2. On a bumpy road: As I discussed previously. Point 1 has to now be balanced against the fact that bumpy road causes a stiff car to lose traction more easily as tire + suspension lose compliance and car becomes airborne. Note that now we are not talking about inside or outside wheels, but BOTH sides, which lift and lose traction.

    I've also read that not only the load on the wheels should be taken into consideration, but HOW FAST that load develops also matters. For example if one increases the compression dampening force too much, the outside wheel will load "too quickly" and the car won't be stable into corners. Basically, it's an exceedingly complex issue and I am happy if I understand anything at all. Smiley

    This is why I've often repeated my opinion of complex coilovers with independent bump and rebound settings: To be reserved for the most experienced of drivers and tuners only! There are numerous parameters to be considered in suspension setting and in many ways the simplicity of the Bilstein is a huge blessing in disguise. (That it is designed and made by the same company that produces the stock suspension and has picture of WR on the web site Smiley make it the overwhelming choice in my book.)


    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

    Ferdie:
    ........... so the amount of force on one single wheel, usually the front outer wheel during cornering, should be kept as low as possible.

    That's got to be an over-simplification, otherwise no car would have an anti-roll bar on it's front axle. Smiley 

    Suspension tuning sometimes appears to be more of an art than a science, probably due to the multitude of complex interactions between all the relevant parts influencing ride and handling.


    --

    fritz


    Re: PASM and damptronics

    cannga:
    high-performance sports car will have a stiffer suspension with a natural frequency of about 120 to 150 CPM (2 to 2.5 Hz).

     

    You are very correct, but there can be complications.

    Imagine if the vehicle chassis has a beaming resonance around the same (2 - 2.5 Hz) frequency range such as the mid-80s Corvettes had.  Their rear suspensions would bounce all over the road because of this condition until the factory fixed it.  One can't believe how spooky those early examples handled.  The rear end would be all over the road if the correct series of bumps were encountered along the way.


    --

    Mike

    2005 Carrera GT - Signal Yellow

    2008 Tesla Roadster - Thunder Gray

    1972 BMW 3.0 CSi - Nachtblau

    2009 Bentley Arnage T - Black Saphire


    Re: PASM and damptronics

    cannga:

    1. On a smooth surface: As you discussed above, stiffer is better because a stiffer suspension reduces weight transfer, hence causes less leaning, and hence maintains tire contact patch of the inside wheels better.

     

    This is very true, as well.

    Old 356 racers would make the suspension so stiff that the wheels barely moved over bumps.  This would completely tame the trailing-arm suspension deflections that gave so much trouble.  Set up this way, the car would skip and skitter over bumps, but corner very well on the smooth spots of the track.  Many SCCA championships were won with this method.

    To have a softer suspension that handles bumps as well as smooth sections seems a miracle of modern engineering.

    I am very impressed with modern Porsche suspension tuning.


    --

    Mike

    2005 Carrera GT - Signal Yellow

    2008 Tesla Roadster - Thunder Gray

    1972 BMW 3.0 CSi - Nachtblau

    2009 Bentley Arnage T - Black Saphire


    Re: PASM and damptronics

    Hi Mike

    If dampers have one optimal setting, do you think that PASM is optimised for the soft setting or the sports setting? Or are both a compromise?

    I would say that they are optimised on the soft setting. I would prefer an optimised sport setting with the soft setting having a little oscillation as a trade off.


    --

    Paul

    996 GT3 RS

    997.2 C2S Cab

    How to Save Money


    Re: PASM and damptronics

    Pink Panther:

    Hi Can,

     Having read about your's and Alex's improvements to the Turbo I have found a turbo that I will swap my cab for. A GT Silver/Cocoa manual with bucket seats. Unfortunately not PCCB. There was a turbo with PCCB in slate which looked stunning but sadly it was tiptronic. So I am thinking through various upgrades:

    1. PCCB - costs a lot of money but possibly worth it for the reduced unsprung mass. Need to research cheaper parts suppliers.

    2. Exhaust - not researched yet but cargraphic sounds like a strong contender

    3. Lighter wheels with Michelin PS2

    4 a. Stiffer springs and Bilstein dampers

       b. Adjustments to toe in and camber

       c. Sway bars

    5. Tuning - might not bother with this or save it for a later date.

    I think it makes sense to do the weight loss mods first as they will effect the spring and damper settings. I hope to take up Alex's offer of a ride in his turbo prior tomaking any decisions.

    The turbo will be used as a long distance tourer so I need to be conservative on changes to suspension for my wife's sake. If she finds it too firm then it won't be fit for purpose.

    My 996 GT3 RS is a keeper although she is currently being repaired after I spun her off the track.

    Turbo + GT3 RS: Sounds like a DREAM garage and this exact combination has been my "secret" plan for a long time. IMO you are having the best of both worlds: daily driver, track car, NA engine's linear response, turbo power.

    Yes, I too think the GT3 RS is a keeper, especially now that you will have all the power you need with the Turbo. I hope the damage to the GT3 RS did NOT extend to the frame or suspension components? IMO, not good if damage occurs there.

    I agree with your mods. This is the triad of mods very common with US owners: suspension, exhaust, ECU. I agree with the order that you are doing yours. It seems like you have been doing very careful homework.

    I believe very strongly in modding one step at a time also. It is good for learning and in addition, if something is not to your liking, you could backtrack and eliminate the mod. This is especially true with the suspension mods; I did mine in multiple steps even though it did cost more money this way. Not too bad, 2 or 3 extra alignments that in the US costs around 180 or so. Very cheap for the lessons I've learned.

    If you mod the Turbo "correctly," my opinion is you will end up with an incomparable daily driver, a comfortable yet extremely aggressive and EXTREMELY powerful Smiley car when situations call for. Even though it's been time-consuming, I would not trade my mod experience for anything else in the (car) world.

     


    --
     

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

    W8MM:
    cannga:

    1. On a smooth surface: As you discussed above, stiffer is better because a stiffer suspension reduces weight transfer, hence causes less leaning, and hence maintains tire contact patch of the inside wheels better.

     

    This is very true, as well.

    Old 356 racers would make the suspension so stiff that the wheels barely moved over bumps.  This would completely tame the trailing-arm suspension deflections that gave so much trouble.  Set up this way, the car would skip and skitter over bumps, but corner very well on the smooth spots of the track.  Many SCCA championships were won with this method.

    To have a softer suspension that handles bumps as well as smooth sections seems a miracle of modern engineering.

    I am very impressed with modern Porsche suspension tuning.

    Interesting stories there. I myself learned of this the hardway, on a 70 mph combination right left right curve from home to work that I drive through daily. The curve has a few bumps in the middle such that if I set my car on stiff setting the rear end feels "funny," like it has a mind on its own. I was new to suspension concepts and was confused; I thought stiffer was supposed to be better in corners.

    I eventually realized that what happens is that on the stiff setting the car bounces off the road, and the centrifugal force, unopposed by tire contact, literally walks the car's rear end sideways. This is made even more dramatic by the extreme rear engine position of the 911 form.


    --
     

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


    Re: PASM and damptronics

    Ferdie:

    What has been left out of the equation so far is the importance of the tire itself. The correlation of applying force and grip is not linear, so the amount of force on one single wheel, usually the front outer wheel during cornering, should be kept as low as possible.

    I meant to post this a while ago. I believe the following discussion & graph are the same as what Ferdie was talking about. The relationship between friction and load is not linear, so as the vertical load on outside wheel increases, frictional force does NOT increase proportionally. The curve plateaus.

    http://www.autozine.org/technical_school/handling/tech_handling_3.htm#Weight-lateral-force
    Look at the following graph. It illustrates the Grip - Load characteristic of a typical tyre.

    As you can see, as the load increases on the tyre, the grip generated by the tire increases, but at a declining rate. This says, when weight transfer to the outside wheel, the grip on the outside wheel is increased, but not increase as much as the grip loss on the inside wheel.
    --

    Regards,
    Can
    997 Turbo + Bilstein Damptronic ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )


     
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