Carrera GT

In my experience, subjective driver "feel" of "hard" and "soft" is usually in the damper rebound, not the spring. Whatever Porsche did with the GT3, I imagine the RS has different springs, at least in the front, and different PASM programming. I don't purport to be a suspension setup expert by any means. For all the accolades, the 911 still runs remarkably ordinary suspension components.

911SLOW

Now we have all the spring rates for all GT3s.


FRONT:

996.1 GT3
PART NUMBER: 996 343 531 91
SPRING RATE: 35N/mm

996.2 GT3
PART NUMBER: 996 343 531 95
SPRING RATE: 40N/mm

996.2 GT3 RS
PART NUMBER: 996 343 531 97
SPRING RATE: 45N/mm

997.1 GT3
PART NUMBER: 996 343 531 95
SPRING RATE: 40N/mm

997.2 GT3
PART NUMBER: 997 343 531 94
SPRING RATE: 49N/mm



REAR:

996.1 GT3
PART NUMBER: 996 333 531 91
SPRING RATE: 65N/mm

996.2 GT3
PART NUMBER: 996 333 531 95
SPRING RATE: 95N/mm

996.2 GT3 RS
PART NUMBER: 996 333 531 95
SPRING RATE: 95N/mm

997.1 GT3
PART NUMBER: 997 333 531 93
SPRING RATE: 105N/mm

997.2 GT3
PART NUMBER: 997 333 531 95
SPRING RATE: 115N/mm

John

Carrera GT

Looks like you'll need to pull a front and a rear out of each car and be able to put it on a dyno with pasm operating and reverse engineer their approximate ranges, measure the springs and decide while the car is disassembled. I'm curious to see what you find in the aftermarket to compare to Porsches lighter spring designs.

911SLOW

Well I have to disagree I think that the problem is quite the opposite.
They abandoned the ordinary components and their evolution and went the PASM way.
Their effort to give the GT3 a dual persona was wrong IMO.

They should have focused on fitting the GT3 with an even better conventional setup: quality adjustable dampers with a few presets for bound – rebound with clear instructions and some medium hardness springs in the range of 600F 800R.
Also they should have addressed the rear toe links issue by eliminating the eccentrics and fit a more solid engine mount as standard.
A setup like that would be capable of performing well in 90% of the tracks and would still take you for a weekend drive if you felt like it.
On a side note the standard tyres should also be road legal and drivable in the rain. And with the above setup you could run slicks for closed tracks.

Nizer

Agree with all except mounts. The dynamic engine mounts are a great engineering solution IMHO.

Everything other observation is spot-on.

911SLOW

They are not standard you pay for them because probably their initial cost must be considerably higher than fitting a 993RS semi solid mount type that would work equally great.

Nizer

Standard in the RS, but I still paid for them

911SLOW

They are? Didn't know that. Thanks.

NJ-GT

For a 2007 Cayman S the spring rates are as follow (measured by RL member running the Cayman Spec rules):

Front: 154# and 174# for PASM
Rear: 228# and 297# for PASM

If the RS Spyder went 10% stiffer in the front and 50% stiffer in the rear, using the Cayman PASM rates as a baseline, the Spyder could be 191# (200# commercial rate) front and 446# (450# commercial) rear.

Consider corner weights and wheel rates to get an initial springs package. Springs are cheap, I buy my Fiat springs under $60 each, so I can fine tune the suspension swapping springs.

For the RS I would start at 600#/900# with Moton Shocks. For the Boxster Spyder I would start at 550#/650#.

You can easily measure wheel rate in your garage, and use the metric system:

1) Put the car on jack stands, keep the tires mounted, put a floor jack under the tire.
2) Measure total spring length and distance from bottom of the tire to the floor.
3) jack up the tire 20mm and measure spring total length.
4) Repeat (3) another 4 times.

The difference between initial spring length and final spring length, compared to the total wheel travel (100 mm) will give you the wheel rate. Repeat on the other side of the axle to confirm.

In the Fiat I have 0.56 wheel rate in the rear, so a 1000# spring becomes an actual 560# spring. All the Porsches 911 using coilovers from the factory (964 I think was the first) use wheel rates close to 1 in the front and around 0.7 in the rear, this is a good ballpark, but the correct approach is to measure it in your garage, and use the corner weight (weight distribution) then determine starting point for spring rates.

There is drastically more information on this, but I like to keep it simple. We could get in the frequency, body flex, tire/wheel sizes, to make it complicated, then throw say bars, track surface, etc.

FTS

The rear spring rates on the Spyder went up 30%, not 50%. Based on what I have seen on few Caymans with coilovers, I do not believe 100# difference between front/rear works very well, I believe the starting point should be 550#/700#, but that's just an opinion

stout

Indeed they did. Sorry, went back to my original text and you are right! Been having some late nights...

pete

savyboy

John, you are awesome! I accept the assitant position Thanks for the numbers. Any chance of official numbers on Spyder F/R?

Thanks NJ-GT!

More good info, thanks Flying Toaster!

Thanks Pete, if by chance you could contact one of the engineers and confirm spring rates that would be incredibly awesome!

911SLOW

You are welcome

..but don't get your hopes up for Spyder numbers. I was trying to get the 2010 GT3 springs numbers and the 24H GT3RS spring numbers for Mooty. He asked me about them in August! and it took me two months and 34 emails.

Porsche is very "tight" on some information. Interestingly it’s easier to find technical information for the regular models than the GT series. I don't know why.

Perhaps now that VW took over, and the next GT3 will share springs with the Audi TTS will have better luck.

Anyway I’ll give it a shot.

Let us know what you r planning to do. After all you are my assistant and I want to keep my profile intact.

stout

Listening to the interview with Van Der Werd right now. It's indeed 10 percent stiffer front and 30 percent stiffer rear on springs, but he says the dampers are NOT just then suited to match the new spring rates. He said the sporting nature of the car gave him more latitude than he normally gets. "We changed quite significantly the damper forces and basically you can say we reduced the rebound side and increased the compression side." He also noted that the front anti-roll bar was made stiffer, while the rear was left the same.

No spring rates, however...

I am curious as to what you're up to, but my guess is you feel the car is too soft at the track and that there's more performance to be had. That may be accurate, but one of the best Porsche road/track chassis guys I know —StrekMichael Levitas —Strekrecently told me he isn't messing with his Spyder's chassis, after all, saying "anything you do will just mess it up." I'd definitely consider that as well as the car's inherent brilliance —Strekas well as the fact that its open structure is part of the suspension tuning equation, too, and thus will limit the impact of spring-rate changes.

That said, I am all eyes!!!

pete

AllanJ

I find spring rate discussions interesting and I've recently bought a couple books to help learn about this area. I also find it interesting that in the case of a 6-GT3, some highly respected race shops out there run equal rates front & rear. Then you have others going with a 200lb split or sometimes even 300lb split. When you factor in the rest of the car (shock settings, canister pressures, sway bars, tire size & type, other suspension bits) and most importantly the driver....you can get a fast car/driver combo any number of ways.

That said, I'm also curious where this particular thread is going. I'm working with my brother on a 914-6 conversion (very flexible chassis) and we're fiddling with that suspension too.