Guys, I am currently running a 997.1TT Champion VTG with essentially a full aftermarket suspension. GMG Sways, Tarrett and GT3 everything else for the most part. There are very few stock parts left as far as suspension goes. Well one of the few items I am not 100% satisfied with as far as suspension goes is my coil overs. Let me first say, changing away from the PASM compatible model is not an option. I don't want the JW Coilovers or other brand. I want the Bilstein PASM models that I am currently running.

With that said, I thought I saw a few of the people here swapping out the springs in the Bilstein Coilovers to stiffer ones and still maintaining the PASM working. Under hard cornering, the car leans too much for my liking and I am thinking that stiffer springs in the coil overs should help fix this problem. Has anyone swapped out the springs in the Bilstein PASM models and if so to what springs? NASA Nationals is a few weeks away and I am seriously considering making this change after the last few track days I had.


See the attached photo for what I am referring to under hard cornering.


Thanks!


-Sayajin

 

Wow leaning is an understatement. That's crazy. Are you using the bigger sway bars from the GT3 RS?

 

I am using the GMG Front and Rear Sways. Yea, I didn't know how crazy the lean was until someone took a picture! With that said, this is an extra tight turn at Autobahn, but still not something I'm happy with!


-Sayajin

 

interesting, I don't feel my car lean much with the GMG springs, sways. What setting are the sways on? Wasn't there a vendor that tweaked the Bilsteins both shock and spring rates? Forget who it was but search a bit, someone mods them.

 

WOW.... that's a lot of body lean. In that pic are you on street tires, R-Compounds or slicks? Looking at that picture you can see a gap between the sidewall and the edge of the wheel on the driver front. So it makes me think they are not street tires.

I'd say your springs are fully compressed and if that's the case, you need a stiffer spring.

I've seen pics of my .2 GT3 in corners like that and it was NEVER fully compressed and leaned over like that. Wow.

 

Running Hooiser R6s. As mentioned above, I was also shocked by the amount of lean when someone showed me the picture. I promise it doesnt feel like that much lean while driving! Also, thats why I made the post, looking for a stiffer spring.


-Sayajin

 

Did a bit more searching and found the thread I originally saw, posted by @Cannga, however the post is a few years old so I want to verify the information is still correct and accurate:

I figure 3 years later there may be more/better options out so I wanted to check before diving in. Thanks!

-Sayajin

 

I agree that does not look right. If you ran super soft racing slicks with a street set up, or something is broken (sway bar end), you would see lean like that.


I have GMG set to the middle setting, I don't get that sort of roll.


As for Bilstein spring rates, with the exception of some of the tuners, Cannga has probably done more research in this space than most.
I believe TPC and Techart run different spring rates on the Bilstein coilovers.

 

Call TPC. They run modified Bilsteins, with straight rates springs in the front. Work well.

 

Sayajin,

Yes the information below is still 100% correct and my car has been set that same way for maybe a couple of years now. For my personal usage (canyon roads and freeway daily drive) and prefrerence, while the car is less comfortable obviously, it is the best that the car has ever felt and car TRULY corners as if on rails, and I could almost guarantee that you will love it. For others who are new to this: there is never a right or wrong in suspension setup, always a trade-off between comfort and handling. What's right for Sayajin, might be too stiff for you, etc.; it all depends on what you are looking for (street vs. track, and if track, how aggressive). The spring rates are the heart and soul of a suspension setup and is the more "correct" way to stiffen you car, as opposed to stiffening the damping force by PASM (never felt right to me), for example.

My car currently is set at 450/600 because I daily drive it, if yours is more for track with little street driving, I would consider 450/650, 500/700, etc. Add R comp tires and the only things faster will be true track setup such as VID997's, etc. Call up Swift and Hypercoils and talk to them directly to get exactly what I wrote below as far as diameter, free lengths; both are highly reputable companies and Swifts may have some rate that Hypercoils does not, and vice versa.

Each spring runs around maybe 100-120 (can't remember exact). The excellent TPC setup follows similar concept: stiffer spring (seems to be front spring only, don't know what rate) and camber plate. If you do it yourself you save a bit of $. I don't believe that you will need the TPC PASM module once you go this route of changing spring - saving even more $. Best of luck and let me know if you have any question.


>>>>>>>>>>>>>>>
https://www.6speedonline.com/forums/...-turbo-17.html
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).

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 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: Helper 80 lb/in spring rate, 60mm length; main 336 lb/in rate, 151.5 mm length; ID 70mm for both helper and main springs.
Rear: Helper 80 lb/in rate, 60mm length; main 565 lb/in rate, 200 mm 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 448 front/600 rear - versus Bilstein's 336/560.
The front spring is Swift Spring part # Z70-152-080: Internal Diameter 70mm, free length 152mm=6 inches, spring rate 8 kgf/mm=448 lbs/inch.
The rear spring is Hypercoil part # 8P0600: Internal Diameter 70mm, free length 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 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!

 

Judging by the photo and the dirt that is kicked up, it looks like you jumped the apex a bit which caused you to come down hard on the left side of the car and really load up the springs. With that said, keep in mind that a 997Cup weighs 2700lbs and runs 1484/1484# springs. Your 997TT weighs about 800lbs more and runs springs that are sofa soft in comparison. Sticking with the Bilsteins, you don't have much of an option but if you're looking for a better performing track set up, you'll need to go up in rates especially running Hoosiers. Your soft spring will really slow you down in fast transitions. If you're dead set on keeping your Bilsteins, I'd call Bilstein and find out how stiff you can go with springs if they revalve your shocks. I doubt you will ever see the performance out of those shocks that you would in a higher end motorsport type shock due to the nature of the construction of the Bilsteins. My car weighs 3200 and I'm running 1400/1500 and it's a fantastic track set up while still street drivable if the road are ok. Just some food for thought...

Tightening the sways will help but having to run overly stiff sway bars is just a band air for a poorly under sprung suspension....

 

Cannga,

Thanks a lot for giving your input! I was hoping you might see this thread. I actually ended up calling Ira @ Tarett, as well as speaking directly with Swift Springs yesterday and both provided me with some great information. Like you mentioned, I am one of those guys who has a track car that is occasionally driven on the street as opposed to a street car that gets tracked occasionally, so my tolerance for "daily drivability" is probably higher than most.

As far as spring rates goes, Swift said that the normal rule of thumb is that you can go +/- 4kg in additional/reduced spring rate based upon what the units normal spring rate is. With that said, Swift recommend a 10kg (560) front spring and 14kg (784) for the rears. They said this is exactly 4kg more and the best option to not have to re-valve the coilovers. They did confirm the sizes and said it is essentially a direct drop in with no modification needed.


In addition, I put a call into TPC and spoke with some very knowledgeable people about their setup. From my understanding, they offer only a front suspension kit that converts you from 70mm ID to 2.5in (essentially the standard) and let you put whatever springs you want in there. They also provide a special camber plate and other components that they believe eliminate some of the play with the rubber items in the bilsteins. We also discussed their PASM mod device and what they saw the benefits where. They informed me that while they don't have a lot of fully built 6 speeders running it, they have lots of race locals that love it. Even mentioned that some people go with the DSC and decide not to change out the springs. They also have a method that allows you to run a different spring in the rear, however it is not a full kit like with the front.

I got quite a bit of valuable information to help make a decision on the best way to move forward. Unfortunately, Swift does not have any of the 10kg 70mm ID 6in fronts in stock, however expect to get some at the end of the month. Also, It doesn't seem that HyperCoil sells the proper sizes for Fronts, only the rears. So I have a bit of time to make a decision either way it seems.

You may be correct about me jumping the apex and creating additional compression, however the picture and corresponding conversation got me thinking about increasing the spring rates above what they normally come with and the general consensus is it seems to be a good idea.

I would have to defer to your expertise as far as the very high spring rates as you obviously know much more about it than I do, however at this point I have my mind sent on maintaing the Bilsteins at least for now. I may track it for a while more and decide I'm ready to make a change, but I'm not there now.

I am hoping that putting a stiffer spring rate on the car will help to address some of the underlying issues that I have so I don't just put a bandaid on it.

Thanks for the help as always!


-Sayajin

 

Very interesting information about the +/- 4 rule of thumb. I've changed my Bilstein post to take this into account - thanks. Good info also about the TPC kit - so the TPC system changes only front spring, not rear, to standard size?

Regarding where to buy the springs, IIRC both Swifts and Hypercoils have a list of dealers, and the springs are actually cheaper buying from the dealers as opposed to buying straight from them (don't know why).

I initially had stiffer springs, I believe 448/672, but found that to be a little too uncomfortable, so I backed down to 448/600, and that has proven to be the sweet spot for my 20 minute x 2 daily drives. Taste/preference varies of course, but you might want to keep these rates in mind if you are daily driving this car. R comp tires also have much stiffer side wall than street tires, and will further contribute to the comfort vs. handling equation.

A story about why I changed from Bilstein stock springs to stiffer ones, and why I think you would very much appreciate the change: around 2009 a professional test driver for a major US magazine and I were out on Los Angeles canyon roads, he on 2010 GT3, me on my Bilstein Turbo, and we switched back and forth for a few hours: in straight lines I caught that GT3 as if it's standing still, but in the curves, especially tight curves, it was total annihilation. I learned two lessons that day: can't race a stiffer car in tight canyon roads, and can't race R comp with soft street tires. :-) I did those two things and now have no further desire to switch to GT3.