yes , I measured using hand held press gauge.
actually my TPMS just about the same with my hand held unit

I checked tire pressure before i start the engine and yes I did select partial load

the weather in indonesia is about 28 degree C in the morning and can reach 40 degree C in the afternoon .thats huge different so the tire pressure chance dramatically from 33 to 36 front and 36 to 41 rear

 

1. Basic Principles:
Say you have installed Bilstein and were happy at first but now want to go to the next step, firmer, stiffer, more like a GT3. What to do? Besides the first and important step of adding R compound tires, this leads to discussion of further modification of the Bilstein, stiffer springs. Note that nothing comes free and this "upgrade" WILL sacrifice comfort for handling. Anyway, IMHO, here are the steps for a "Turbo to GT3 conversion":
1. R compound tires: Don't ever underestimate the difference a tire could make. This is a key component of imitating GT3: you want GT3 handling, you need R compound tires such as Michelin Cup, Pirelli Corsa, Toyo Roxes R888, etc. No way around this. Why? Not just increased traction, but more importantly the stiffer tire sidewall that hugely influences suspension behavior (makes the car stiffer with less body roll).
2. More negative camber, -1.2 front, -1.6 rear. This means you max out the front negative camber, and keep rear camber same as factory setting of -1.6.
3. Stiffer and adjustable anti-roll bar. For adjustment of understeer/oversteer, body roll, and ride comfort. Combine this with rear Tarett Drop Link Here for even better feel of tightness and control - you will love it, guarantee.
4. Bilstein basic or with stiffer springs: A basic Bilstein with R compound is outstanding and already transforms your Turbo to something that is very fast. However, if you want to take the GT3 in tight corners & curves, and if you want to duplicate the subjective feel, IMHO even stiffer springs are needed. This is where the beauty of using coilover comes in: it's designed with that in mind, the ability to change springs to your need and taste.

2. How to change springs for Bilstein:
Keep in mind there is a limit as to how much you could increase the spring rates. Per Swift, the normal rule of thumb is that you can go up to +/- 4 kgf/mm (224 lbs/in) in additional/reduced spring rate from the coilover's stock rates. What this means is that since the Bilstein starts at 336 front/560 rear, you could go up to about 564 front and 784 rear without having to re-valve your Bilstein shock absorber. For reference, a 911 professional race car would run in the 1000-1200 spring rate range (anyone pls correct as needed).

First some basic technical information for the Bilstein springs - they are weird in that their ID is 70mm, not industry standard and making it difficult to find replacements. Second, don't worry about changing the helper springs (in the Bilstein these do not contribute to the rate; they are "helper," not "tender" springs), all you need to change are the main springs:
Front: Main Spring 336 lb/in rate, 151.5 mm length; Helper Spring 80 lb/in spring rate, 60mm length ; ID 70mm for both helper and main springs.
Rear: Main Spring 565 lb/in rate, 200 mm length; Helper Spring 80 lb/in rate, 60mm length ; ID 70mm for both helper & main.

There are two places you could get springs that fit Bilstein: Hypercoil and Swift Springs. The springs you want to look for is 70mm ID, 6 inches long front, 8 inches long rear. The process is very easy and cheap - labor should be around 300-400 per axle.
Swift Springs: http://www.swiftsprings.net/products...r-springs.html
Hyperco: http://www.hypercoils.com/PDF/70mm.pdf
Currently my car is set at 392 front/600 rear - versus Bilstein's 336/560.
The front spring is Swift Spring part # Z70-152-070: Internal Diameter 70mm, free length 152mm (6 inches), spring rate 7 kgf/mm=392 lbs/inch. (Previously # Z70-152-080 spring rate 8 kgf/mm=448 lbs/inch)
The rear spring is Hypercoil part # 8P0600: Internal Diameter 70mm, free length 203 mm (8 inches), spring rate 600 lbs/inch.
The springs are cheap and directly replaceable for the OEM Bilstein springs. If you are into more advanced level of suspension tuning, the springs are the place to play around and have fun with. It's an easy process and the change will be easily noticeable.
The stiffer springs make steering response more immediate (no free play) and precise. Soft/mushy steering IMHO is one of the biggest problem of the stock Turbo compared to its GT2/GT3 sibling. The car is definitely on the firm side but has extremely fast reflexes and minimal body roll. This is the best all around car that I've ever driven: for me, perfect mixture of handling vs. comfort, precise steering, precise suspension response. I love every second that I am driving my Turbo baby!

 

What R compounds are you running on the street?

 

Excellent write-up and thread..thanks

 

I had Pirelli Corsa for 1 year and recently changed to Michelin Pilot Super Sport for the rainy season. By spring I plan to get another set of R comps, this time most likely Michelin Cup, non N rated and please don't make me explain LOL. There is no reason for the switch other than I want to learn the difference and I want to try different things for the fun of it. I *loved* the Corsa. FWIW rumor, pure rumor, is that the Michelin Cup is a little stiffer than Corsa, and not as sticky in the rain. It is also cheaper.

Toyo Roxes R888 is another candidate - but I have some concern about possible louder road noise (rumor again - no flame pls, from reading post here and there), plus the weight is higher. Keep in mind that all of these R comps get unusually louder and stiffer towards the end of their life cycle. In other words, very uncomfortable.

If you've never had R comps before, get ready to be amazed. Check out this thread also: https://www.6speedonline.com/forums/...stiffness.html
Thanks for the nice comments guys.

 

Following are some technical data of Bilstein PSS9; NOT for everyone and only try to read this if you are sort of nutty . I am re-posting here because it's very rare that you see complete data like this.
I highlighted in red numbers that are interesting: the max allowable increase in spring rate (around 100-150) before one should re-valve the shock, and range of dampening forces when you change the Bilstein setting from full soft to full stiff.
Note that these are numbers for different cars, NOT our 997 Turbo. For one, the starting spring rates of 997 Turbo Bilstein are higher, 336 front/ 560 rear.

FWIW, I am currently running mine at 448 front/ 5600 rear, using 70mm ID, 6 inch springs from http://www.swiftsprings.net/file/metric.pdf, and I absolutely love it. The stiffer front spring rates help a lot with making steering firmer and more precise, with no significant increase in understeer. In the 997 Turbo, stock steering is too soft/mushy (over assisted); this is among my biggest criticism of the Turbo so this change as a result of stiffer springs is very welcome.

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https://www.6speedonline.com/forums/...-bilstein.html
SPRING RATES:
8848/8877/D536:
f: 260 lbs/in main, 145 lbs/in tender -- r :515 lbs/in main, 145 lbs/in tender
Initial combined rates w/o static sag:
f: 93 lbs/in -- r: 113 lbs/in
Final rates before main coils close:
f: 260 lbs/in -- r: 515 lbs/in

VALVING: (max force)
8848 (PSS9):
9 = soft/adjuster open, 1 == hard/adjuster closed
Rebound (in N):
f: 9=1465, 1=2050 -- r: 9=2150, 1=2820
Compression (in N):
f: 9=935, 1/1=1410 -- r: 9=1310, 1=1530

-- Max Spring Rates supported w/o revalving:
f: 350 lbs/in main -- r: 650 lbs/in main (6.3kg/mm -- 11.6kg/mm)

8877 (PSS9):
9 = soft/adjuster open, 1 == hard/adjuster closed
Rebound (in N):
f: 9=1700, 1=2775 -- r: 9=2270, 1=3060
Compression (in N):
f: 9=1050, 1=1695 -- r: 9=1420, 1=1800

-- Max Spring Rates supported w/o revalving:
f: 375 lbs/in main -- r: 700 lbs/in main (6.7kg/mm -- 12.5kg/mm)

D536 (PSS10):
1 = soft/adjuster open, 10 == hard/adjuster closed
Rebound (in N):
f: 1=1700, 10=2775 -- r: 1=2270, 10=3060
Compression (in N):
f: 1=1050, 10=1695 -- r: 1=1420, 10=1800

-- Max Spring Rates supported w/o revalving:
f: 375 lbs/in main -- r: 700 lbs/in main (6.7kg/mm -- 12.5kg/mm)

Bilstein will revalve each strut for $125.

It would be interesting to compare valving data and spring rates for other shock models too, if anyone has that data.

Instructions:
gm5-8848_C4 Manual
gm5-8877_Turbo Manual

 

Very nice post on caster -- rarely seen discussed! BTW if you ever wonder what caster looks like, look at the 2 front wheels of Supermarket's cart next time you go shopping LOL - how the axis come at an angle and allow the front wheels to steer and straighten itself as you push the cart.

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http://www.planet-9.com/<wbr>cayman-boxster-modifications/<wbr>16158-installing-gt3-front-<wbr>lower-control-arms-2.html
How cool! A way to progressively increase the tilt of the tire as you turn the car harder! Let's put A LOT of that on! And, if you look at the front wheels of almost any German high-end car when it's parked with the wheels turned sharply. Others are catching up, but I really am amazed at how much caster is dialed in to some of these suspensions.
But the benefit doesn't stop there. Positive caster also makes the steering wheel more self-centering and everyone likes that, right?
Well, like everything else, there's a limit. You don't get a corresponding camber change at the back, so you can really create some wicked oversteer situations on a rear drive car, especially one with a solid axle.
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>>>>>>>>>>>>>>>>>>>
http://www.ozebiz.com.au/racetech/theory/align.html
THE EFFECTS OF CASTER
Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the caster is negative.
Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. The mechanism that causes this tendency is clearly illustrated by the castering front wheels of a shopping cart (above). The steering axis of a shopping cart wheel is set forward of where the wheel contacts the ground. As the cart is pushed forward, the steering axis pulls the wheel along, and since the wheel drags along the ground, it falls directly in line behind the steering axis. The force that causes the wheel to follow the steering axis is proportional to the distance between the steering axis and the wheel-to-ground contact patch-the greater the distance, the greater the force. This distance is referred to as "trail."
Due to many design considerations, it is desirable to have the steering axis of a car's wheel right at the wheel hub. If the steering axis were to be set vertical with this layout, the axis would be coincident with the tire contact patch. The trail would be zero, and no castering would be generated. The wheel would be essentially free to spin about the patch (actually, the tire itself generates a bit of a castering effect due to a phenomenon known as "pneumatic trail," but this effect is much smaller than that created by mechanical castering, so we'll ignore it here). Fortunately, it is possible to create castering by tilting the steering axis in the positive direction. With such an arrangement, the steering axis intersects the ground at a point in front of the tire contact patch, and thus the same effect as seen in the shopping cart casters is achieved.
The tilted steering axis has another important effect on suspension geometry. Since the wheel rotates about a tilted axis, the wheel gains camber as it is turned. This effect is best visualized by imagining the unrealistically extreme case where the steering axis would be horizontal-as the steering wheel is turned, the road wheel would simply change camber rather than direction. This effect causes the outside wheel in a turn to gain negative camber, while the inside wheel gains positive camber. These camber changes are generally favorable for cornering, although it is possible to overdo it.
Most cars are not particularly sensitive to caster settings. Nevertheless, it is important to ensure that the caster is the same on both sides of the car to avoid the tendency to pull to one side. While greater caster angles serve to improve straight-line stability, they also cause an increase in steering effort. Three to five degrees of positive caster is the typical range of settings, with lower angles being used on heavier vehicles to keep the steering effort reasonable.


Like a shopping cart wheel (left) the trail created by the castering of the steering axis pulls the wheels in line.

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Hope this helps those completely new to this. Anyone please add/correct me as needed. I will edit as necessary.

Suspension Mods Overview:
Suspension mod is easier to understand if you categorize the modifications. Then all of sudden, things will seem so simple ;-) and not so intimidating. I will arbitrarily create 4 categories:
1. Stiffer springs: this is the single most important mod in the Turbo and will transform the car. It is accomplished by using lowering springs (which I do not recommend but YMMV - ok if you prefer them) or using coilover (springs + shock absorber) such as those made by Bilstein or KW. Positives: Stiffer and lower are almost always better in a sports car: less weight transfer (body roll, dive and squat), more precise response. Negatives: Ride versus handling trade-off is forever present - the law of physics. As handling improves, ride will suffer. Don't use Moton or JRZ because they are too stiff for street driving.
2. Alignment: involves toe, caster, camber. For all practical purposes, all you need to worry about in the Turbo is to increase front negative camber. Stock is around -0.6, you want to increase this to minus 1.1 or so (the max possible). Positives: Negative camber increases cornering force/traction of the tire (allows you to corner faster), decreases understeer which is an inherent problem with AWD 997.1 Turbo (complicated, pls just trust me that this is the case ;-)), improves turn-in. Negatives: Excessive & uneven tire wear and straight-line traction/acceleration could be affected adversely if over-done.
3. Stiffer "other" components: This would fall into 2 categories:
A. Sway bar: used to fine tune the system, in particular the understeer/oversteer behavior. After market sway bars are not only stiffer, they have adjustable stiffness. In the AWD Turbo with inherent understeer trait, the recommended setting is soft front, stiff rear, to decrease understeer. Note that sway bar on stiff setting could have major effect on the comfort of your ride (very un-comfortable). Positives: Decrease body roll, adjust understeer/oversteer, stiffer front sway bar makes steering firmer and feel more precise. Negatives: Decreases ride comfort.
B. After market suspension links that use solid metallic bushing/joint, in place of stock rubber/neoprene bushing/joint. The links include rear upper links (dog bones), toe control link, thrust arm bushing, front camber plate, drop links, etc. Positives: Solid links increase precision and make cars feel more "planted"/precise. Negatives: Increase noise, vibration, harshness, some more than others. Also, these are wear-and-tear items and need to be checked periodically and replaced when the joints become loose (metallic joints/links don't last as long as rubber/neoprene joints/links).
4. Tires: Don't under-estimate this major component of suspension system, and never race another car that has superior tires! This means: R compound tires such as Michelin Cup or Pirelli Corsa. Positives: have inherent advantages: stickier rubber, stiffer wall. Negatives: Dangerous on wet roads (no traction, aqua-plane), takes time to warm up, noisy & stiff especially when old.

 

excellent synopsis Can. The only small point I would add is that Moton (under different ownership now, original company re-organizing under different name) and JRZ manufacture the dampeners/shock bodies and not the springs. The Moton/JRZ shocks can be valved to match whatever range of spring pressure desired. Whether you wanted JRZ's valved to near stock spring pressure ~150# or track pressure ~1000# they could do it.

 

Nice JOB!

 

Spring is here - time to take pictures again.
No not Spring, spring! Here in my garden:

 

The green spring is Swift front spring, light blue is Bilstein OEM, dark blue is Hypercoil rear spring.
Why springs? From previous post:

>>>>>>>>>>>>>>>>>>>>>
https://www.6speedonline.com/forums/997-turbo-gt2/136096-pics-review-my-bilstein-pss10-lowered-red-turbo-17.html
Say you have installed Bilstein and were happy at first but now want to go to the next step, firmer, stiffer, more like a GT3. What to do? Besides the first and important step of adding R compound tires, this leads to discussion of further modification of the Bilstein, stiffer springs. Note that nothing comes free and this "upgrade" WILL sacrifice comfort for handling. Anyway, IMHO, here are the steps for a "Turbo to GT3 conversion":
1. R compound tires: Michelin Cup, Pirelli Corsa, Toyo Roxes R888, etc. No way around this. If you want GT3 handling, tires with stiff sidewall is a prerequisite.
2. More negative camber, starting numbers: -1 front, -1.6 back. More as needed.
3. Stiffer and adjustable anti-roll bar. For adjustment of understeer/oversteer, body roll, and ride comfort.
4. Bilstein with stiffer springs: A basic Bilstein with R compound are outstanding and already transforms your Turbo to something that is very fast. However, if you want to take the GT3 in tight corners & curves, and if you want to duplicate the subjective feel, IMHO stiffer springs are needed. This is where the beauty of using coilover comes in: it's designed with that in mind, the ability to change springs to your need and taste.

Keep in mind there is a limit as to how much you could increase the spring rates. In general, you could increase the spring rate about 100-120 lbs/in or so; beyond this, the shock absorber has to be sent in to be re-valved. What this means is that since the Bilstein starts at 336 front/560 rear, you could go up to about 460 front and 680 rear without any modification needed. For reference, a 911 professional race car would run in the 800-1200 spring rate range (anyone corrects as needed).

There are two places you could get springs that fit Bilstein: Hypercoil and Swift Springs. The springs you want to look for is 70mm ID, 6 inches long front, 8 inches rear. The process is very easy and cheap - labor should be around 300-400 per axle.
Swift Springs: http://www.swiftsprings.net/products...r-springs.html
Hyperco: http://www.hypercoils.com/PDF/70mm.pdf
Currently my car is set at 448 front/600 rear - versus Bilstein's 336/560. The front spring is Swift Spring part # Z70-152-080, the rear is Hypercoil part number 8P0600. The stiffer springs make steering response more immediate (no free play) and precise (soft steering IMHO is one of the biggest problem of the stock Turbo compared to its GT2/GT3 sibling). The car is definitely on the firm side but has extremely fast reflexes and minimal body roll at sub 100 mph speed. This is the best all around car that I've ever driven: for me, perfect mixture of handling vs. comfort, precise steering, precise suspension response. I love every second that I am driving my Turbo baby!

 

Haven't seen you around here in quite some time, Can. I thought maybe you sold your car. I'm turbo-less but still visit here.

 

Hey Cannga - have you upgraded your front/rear sways? ...what about thoughts on Engine mounts? The guys at Sharkwerks just launched a set of RSS ones - the mounts that is, that look VERY promising.

BTW - my RSS sways from Sharkwerks arrive tomorrow

You're an expert when it comes on coilovers/spring but never heard you mention any other components/elements that could provide more benefit. Thinking that eventually you're going to reach a point of limited returns playing with shocks and springs(?)

 

Latest pic of my Turbo baby; this one on the switchback in the neighborhood around my house. Now you know why I am always searching for "stiffer and lower"; the curves are not kind to soft suspension and these roads are what I drive through daily.