-I'm starting this thread in hopes that it'll help all of us collectively agree as a community on some of the more common issues and solutions for the 996TT platform!

First, let's look at what the suspension consists of and what is lacking...

According to the books I’ve read on the development of the 996TT, the original intent of the suspension on the 996TT was to create a great Grand Touring, sporty and comfortable ride. It was not intended that the stock suspension be used as a road race platform. An inspection of the bushings and mounts for the suspension and drive train will show them to be very soft and compliant. Further, any upgrades to the engine/turbos will create excessive movement or porpousing of the drive train. Excessive movement can pull on intercooler hoses, vacuum lines, and cause the exhaust system to make contact with the rear bumper cover.

The basic design of the 996TT is similar to that of the other 911s based on the 996 chassis, except for the fact that the AWD system requires a different front suspension design/geometry, and the pickup point of all four corners is altered to accommodate this 4 wheel drive solution.

The 996 Turbo has a different offset to the front suspension upright/knuckle and this plays into the issues of compatibility for front brake rotors, as described in the Brake tech DIY sticky I started elsewhere in this category.

Toe and camber are adjustable on the 996TT from the factory, although camber is limited to approximately 1.5 degrees negative front and 2.0 degrees negative rear. Caster can ONLY be altered via the strut mount at the top of the coil spring and is very limited in adjustment in that range. OEM right height is not adjustable on the 996TT (However, the GT2 does have threaded collars for coil over ride adjustment.) and the sway bars are not adjustable. The X73 suspension package offers springs that are approximately half an inch lower with a few other improvements in stiffer bushings. The struts on both the standard and the X73 are valved specifically for the grand touring intent of the chassis.

There are a number of “solutions” that people have asked about… Some want to alter the ride height without creating a less comfortable daily driver. Others want to drive at the track occasionally while using the car on weekends and for fun. Still others want the best of both worlds; GT3 handling with GT2 power…

So if we're talking "levels" then I suppose we could try something like this:

Level 1 - OEM Stock
Level 2 - Coil overs for asthetics
Level 3 - DE beginners
Level 4 - DE Advanced
Level 5 - Club Racers (Tom Kerr on Crack! )

Let's start a discussion and I'll edit this initial thread as we go to keep everything in the first thread. I also plan to do that to the Brake DIY so people don't have to read 20 pages to find the answers they're looking for...

Here is some interesting Tech info from the Factory Service Manual:

Scaling and Corner Balancing - Maximum Load Differences for the GT2, per wheel axle should be 15 KG – Adjustments made at diagonal corners for balancing (e.g. right front to left rear)
Ride Height for the GT2 – Front - 118MM minimum up to 123MM Rear – 133MM Minimum up to 138MM. Total per axle is 5mm adjustment

There is much variance on Turbo and Turbo X73/S models
Standard 996Turbo Front - 158 +-10MM Rear – 163 +-10MM
RoW Front - 138 +-10MM Rear – 153 +- 10MM
X73 Model Front - 128+-10MM Rear – 133 +- 10MM




Mike

 

I am suscribed 100% to this treat, I am level 3 I guess, I do about 20-25 AutoCross events a year and a couple of DEs. The rest is pure backroad weekend fun . I dont care too much about comfort but at the same time I dont think I need a full racing setup, also I dont want to spend too much money either..

 

I have used the thread below as a reference for suspension mods for the 996TT platform since I discovered it a few months ago. You are probably aware of it already. Using your framework I would put this into Level 4.

https://www.6speedonline.com/forums/...uspension.html

I am in the process of evaluating a 996TT build for the track so your thread is of great interest to me.

 

contact me for this info at dat74z@yahoo.com

 

If you are looking just to adjust the height and have no plans of tracking the car, would springs be OK or a waste of money?

If so any brands that fit well in the 996tt?

 

Personally, I don't care for them. For the cost of swapping them and then doing another alignment, you might as well save the money for going to something more sophisticated. But others will disagree... And your timing was great. I was editing the post for coil springs as you posted... Go to my second post...

Mike

 

mike im running the JIC with TPC racing adjustable front and rear sways, adjustable rear toe's. but damn even at the softtest setting they are still on the stiff side .

 

Mike-

Thanks for the thorough discussion. As you mention towards the end of your comments the investment adds up quickly. I completely agree; I use a custom Stasis/Ohlin Motorsport system in my VW R32 track car. My experience with the Haldex AWD system in that car has inspired my interest in the 996TT platform.

A couple of areas of interest;

First question; AWD system. The OEM VW Haldex system is FWD biased (primarily oversteer). In addition the OEM Haldex is free wheeling under braking (not desirable under heavy braking on the track). Tuning the suspension for the track requires modification to the Haldex to optimize ones ability to balance the suspension front to rear (throttle oversteer, etc.) as well as stabilizing the rear drive train under braking. Fortunately the Haldex can be custom tuned to provide a RWD bias and to effectively "lock" the rear diff under braking. What is the bias rear to front of the Porsche OE AWD system? Are there custom tuned versions available (I doubt it since it is a viscous coupled system)?

Second question; any discussion of suspension should include the tire/wheel combination. One of the biggest challenges for the stock VW R32 is the fact that it runs on 225/40-18 tires (we use Hoosier R6 rubber in the dry but lately I have been very impressed with the latest BFG g-Force R1). I have struggled to find/fit wheels and tires with the proper offsets that maximize contact patch and take advantage of the suspension and drivetrain upgrades we have made to it. What are the recommendations for wheel/tire combinations for the Porsche 996TT platform that you would consider level 4 or beyond?

 

I've had springs and there is nothing really wrong with them. They are the cheapest part of any suspension. As long as you can get a decent labor rate the asthetic bang for the buck is very good. If your car isn't going to be pushed much, springs are decent, but aftermarket springs tend to sag after a while and you may need to swap them again down the road.

But that's no different that coilovers which require periodic (or MORE PERIODIC) maintenance based on the brand.

Also of note is the make sure coilover providers have good service, look around, some coilover manufacturers have crap for service and repair. I happen to live about 35 minutes from Moton USA and that was a big sway in which direction to go for me.

 

Thanks for your time and effort Mike. I'll be following this.

 

Wow, Great info! Thanks. Always good to have a quick reference.

 

Mike,

Getting into a technical discussion of suspension dynamics as you mentioned early in this thread would possibly go over the heads of the majority of us and beyond the interest level of most.

I've been studying and trying to learn a little about suspension dynamics lately since I have made a lot of changes to my car. I have found this subject to be highly-detailed, extremely convoluted, fiercely interdependent in component relationships and sometimes very confusing (for me, at least).

For instance, I have been trying to evaluate the ride height of my car to determine if it is at its best position. One might think that just slamming it down as far as components permit would be the best thing to do in order to lower the center of gravity (CG) and improve cornering and straight-line capabilities. I'm not so sure about that. With our 996tt street-car geometry and suspension pickup points this creates somewhat of a quandry. If the ride height is really low, the suspension arms angle downwards and with some measurement and calculation it will be seen that the front view static roll centers (RC) at each end of the car are below ground. With cornering forces, they will go further underground. Well so what, you say. This increases the distance of the RC from the CG. With that increase comes more rolling force (hence chassis roll) because of that increased distance. This must be offset with heavier springs/roll bar stiffness, etc. At the other end of the spectrum in placing the RC closer to the CG by raising ride height to where the RC's come above ground you decrease that rolling moment but increase the jacking effect on the sprung weight. With my limited knowledge I'm not sure what the correct RH should be.

I read that Porsche made suspension changes in the '04 GT3RS that allowed a low ride height without the RC's being underground. They must've thought this was an improvement because the earlier models were underground as are mine.

There are many things that can be calculated for our cars such as CG, instant centers, roll centers, wheel rates, etc. but some of these equations require a lot of measurements that would be difficult to determine accurately without a whole lot of time and trouble.

I've had my dampers, springs, ride heights F and R, alignment specs, etc. all done by a shop that has set up cup cars in the past. Only problem is that I ain't got a cup car, and don't want one. Their efforts, at best, are educated guesses. I won't know what I really have until I get to the track, hopefully this weekend if the wx is good.

I haven't found, at this point, anyone who has a large amount of experience and an associated data base to give the correct starting points for an AWD 996 turbo. And oh yes, let's not forget to throw in lot of aero downforce into the mix. That's my dilemma, and I expect is the same for others who want to do some tracking.

It would be nice to have someone with that knowledge to share recommendations.

 

I have the pss10 set 8R3F, ride height lowered approx 1.3 inches, otherwise stock. What do you do to tune out some understear. Would adjustable sways full hard back and soft front be a good option? Call me a level 2.5.

 

Matt Callahan has a shop in North Carolina that has done extensive work on his 996GT2. That car is simply brilliant in its setup and quite honestly one of the most well sorted street/track cars I've ever been in...



Mike

 

Main issue I have with GT2 data is that front suspension geomertry is different bc it doesn't have to accommodate half shafts and we, as 996tt owners do. Removing the 71 lb. package of shafts, coupling, etc. does not a GT2 front suspension make. We still have all the same geometry and pick up points, AWD or 2WD. As you well know, the front is the most important even though we are all crippled with a McPherson strut design.