When I read the discussion on the spring rates in Mikymu "for sale threat" I figured I would start a threat myself on my current experiment.

I've been tracking my current RS for about 3.5 years now and have about 27K miles on the car, probably 1/3rd on the track. I have the R&P and had Tarrett rear control arms and that was about the extend of it. Although I no longer have any chance of catching Peter with his new RS, I've kind of plateaud with my current setup. Since I'm too lazy to fiddle constantly with my suspension I've decided to just change the spring rates on my car instead of purchasing adjustable shocks/springs from KW, Moton or JRZ.
Today I picked up the car from Orbit Racing after Roger made some hats so that we can fit linear Eibach springs on the car instead of the progressive H&R's that are on the car. As Utkinpol posted in regards to TPC setups, the spring rates are wayyy up there and right now we have no difference at all between front and rear. I've asked Roger about the big difference between front and rear that I see constantly mentioned on this board (200-300lbs) and he stated that on his spring test machine the difference between front and rear from the factory was rarely more then 70 lbs, no matter what the springs indicated.
My current setup with the helper springs is 1000 lbs front and rear. I drove it home expecting my teeth to rattle out, but there is barely any difference at all, even with suspension set on hard.

This weekend is our annual instructor school at PBIR, so that will be the first test. Main problem is that PBIR is as flat and smooth as my kitchen table, so I'm not sure what the results are going to be. We may change springs on Sunday depending on how the car handles. The week after that we have Winterfest for 4 days at Sebring and that is my main track that i want the car to be set up for.

I will post progress (or lack thereoff) during the coming 2 weeks. The starting setup will be:

1000F/1000R
Corner balanced, adjustable links on sway bars installed
Camber 2.5 rear, 2.7 front
ride height set to 97/115 mm on my 18" rims
New cup rear tow arms, Tarrett arms were worn and allowed 2 mm play tow
Already had the GT2 rear sway bar.

Best PBIR times are in the 1:26 area on RA1's and Nito's.

 

Excellent Erik and can't wait to get your feedback. As you can see I know next to nothing when it comes to shocks and springs other than the fact I know our RS don't run on leaf springs like Z06 lol

I will post NJ-GT's spring recommendation on factory shocks below for other to reference:

You can get a set of the following

•(4) Genesis Spring isolators (60mm ID)
•(4) HyperCo 4" Zero Rate tenders (60mm ID)
•(2) 6" x 60mm ID 450# springs for the front and
•(2) 6" x 60mm 750# at the rear

The RS has close to 1:1 motion ratio in the front and 0.7 in the rear, the RS stock springs are 225# front and 550# rear, but applying the motion ratio they become 225# and 385#, which by the way represents a 37% of the sprung weight in the front springs and 63% in the rear, very close to the actual static weight (great job by Porsche).

So, the 450# and 750# springs allow you to keep the same balance as stock (37%/63%), and you can reuse your stock shocks. There is no need to revalve the PASM shocks for these springs, and the car will work plenty better. The ideal spring rates for track/street use on DOT-R tires are 600/900 for the 997 and 600/800 for the 996, but these rates require new shocks ($$$).

 

If I remember correctly, the front spring rate of the 7.2 GT3/RS is 45 Nm and rears are 105. If that is right, that about 400 lbs/in front and 930 lbs/in rear. Again, if this is all right, it is certainly a lot more than 200 lbs difference front/rear in stock form.

 

Does Tarrett sell the monoball replacement? Or once the joints are worn, you have to replace the whole thing? Seems like not an economical way to go.. ? (you mentioned that you replaced the Tarrett toe arms w/ the Cup unit now)

 

tarett may replace those joints most likely if you complain.

i have rear tarett droplinks and one of them got a significant play that resulted in severe rattle - tarett sent me a replacement 10mm rod end for free.
they use mostly ERP rod ends - very good quality teflon wrapped stuff, it should be good for a long long time.

 

with stiffer springs at PBIR the car will fell like its on rails.. with stiff springs at sebring.. you teeth will fall out and the car will be hopping around the track and under hard braking... that is the 1 reason you want DA shocks.

after you pay for labor of removing and installing springs 4+ times you could of had a set of DA shocks, especially with the great deals of a used set of motons out there.

I have a NB 997 and I run:
Tires: Yoko Slicks (240/280)
Camber: -4 F -3.7 R
Springs: HyperCoil 900/1100
Shocks: JRZ RS PRO

Car feels like its on railroad tracks

 

Correct, the 997.2 GT3 RS has stiffer springs than the 997.1 GT3 RS. However, your conversion is off.

Using the correct multiplier of 5.7111

2010 GT3 RS:

Front : 257#, or 250# on commercial specs (Swift or HyperCo)
Rear: 600#

The 2010 GT3 and GT3 RS front sway bar is stiffer than the 2007 cars (thicker).

RA-1 require stiffer springs than OEM MPSC.
R6 and A6 require stiffer springs than RA-1
Michelin/Yoko/Pirelli slicks require a lot stiffer springs than A6/R6 and lots more negative camber.

My recommendation above is strictly for the 2007-2008 GT3 and GT3 RS, I'm not familiar with the shocks on the new car. Beyond those rates, rebound control becomes a problem with the stock shocks.

So, to the OP: run that setup, then try the 450/750 and compare lap times. 997.1 Carrera S are running low 1:25s at PBIR.

I ran 550#, 650# and 1000# rear springs in my 996 GT3. 800# was the ideal for that car on DOT-R tires but I used to run on bumpy tracks and autoX lots so the 650# work better.

In the Fiat I have experimented much more, 650#, 900#, 1100#, 1200#, 1500# at the rear, 475#, 600#, 850#, 1100#, 1200# at the front. My current ratio is very close to Challenge specs and factory street car, at one point I tested the 1100/1200 combo and the understeer was annoying on slow speed turns, but high speed turns were almost a flat-out thing, easier car to drive but slower on the timer.

 

Sound great ... but I really don't want to spend another $7K on mods if I can avoid it. I will see if I can sneak into mooty's garage tonight and swap out his moton with my factory pos. He will never know the difference

 

Hey Rad

Thanks for the input. Too bad you are at Florida ... I could really use your help here at California. Will try out the stiffer springs on my factory RS and see how it feels. It is way too soft on my current setup with Kumho V710

 

You are close : ) 7.2GT3 is 49 and 115

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

 

Rad, this is indeed going to be the experiment. And PBIR is not going to be the deciding factor, it has to be Sebring. This of course is going to be a compromise, but I rather be faster at Sebring then being faster at PBIR. But I do know that Roger/Orbit is very very good on setting up cars. Orbit has done it all, won the 24 of Daytona, was always in the top 2 of the Porsche Teams in qualifying in ALMS when they still ran there etc etc. His latest addition/newest mechanic came from Manthey who of course also knows a thing or two.
p.s. I don't know or have I ever run with any stock Carrera S's on regular R compound (not slicks) that were close to 1:25's. Peter (Trakcar), Juan Poro (regular 997 GT3-1) and I are usually among the fastest with PBOC or PCA. I assume Derek in NASA will probably do 25's in his 997S, but car is not exactly stock. But I know he's very fast, I at one point had him as sign off candidate for Super Solo. Either way, I hope to meet you soon now that you're in FL.

Mobonic, of course a full system is better and faster. But I'm just not the guy that goes to the track with setup sheets for every track. I wish I was like Rad in that respect. I love reading his posts, because he's willing to try and experiment constantly. I'm very lazy in taking data, analyzing data, etc etc. After my tire temps and pressures are correct on my car, I'm done fiddling.
Regarding cost, springs are cheap, the ones I don't use go back to Orbit who has a whole attic full of them. And they change a set of springs in about an hour.

 

Rad,

Are you coming out the Sebring?

It will be fun, who cares about PBIR setup..
Erik will correct if I got it wrong when he gets home; Erik is running slower this weekend and the temps are cool enough to post low times. Setup has too much understeer, he has to wait too long before going on the gas, could also be tires, or just a bit less grip after the rain...
Last night they switched to 700F and 1000R, a little better, but still feels slower.

Orbit will be at Sebring so we can screw around with both RS-es this weekend.

There is a real difference is shocks; I could not run shocks hard in GT3.1 at Sebring in T17 and T1 but the RS.2 is much faster all around in hard setting, no problem in T17 and T1. The RS.2 on hard seems perfect for Sebring, but that is maybe becasue I don't know what better feels like.

I describe the RS.2 as softer, but I think the car's weight is less bouncy and just more managable going on and off the brakes as well as cornering. Could it all be DEM's and a bit higer ride height? (Compared to my GT3.1).

Erik; As good as my car feels compared to old car, I would lean towards going in that direction.
911slow's numbers show rougly 20% increase front and 10% increase rear. Maybe just double the difference? Or is that too simple?

I wonder why the spring rate would be almost even on CUP cars and only 50% front to rear for street car.

 

Aaah, thank you for the correction

 

Sebring possibility is pretty high, awaiting work schedule, at least I will be in Florida all week and not somewhere else.

Cup cars have much wider front tires compared to rear (240 front, and 270 rear), so they need more springs to keep the car balanced. The street car uses 235/325 (huge split in width).

Generally, the higher the speeds on turns, the more front spring you need. In autocross for instance ( 30 mph turns) the front needs to be a lot softer (we are talking GT3 here), but such setup becomes too lose at a tight racetrack (i.e. Streets of Willow). You can run a stiffer front spring, or just move the sway bar to a stiffer setting. Eventually it will be balanced.

Then you take the car to a track where turns are taken at higher speeds, the car will be loose again, so make the front stiffer (springs or stiffer sway bar). As you keep increasing front spring rates the car will be more stable on the high speed stuff, but slow turns will be frustrating due to understeer.

Most Porsche SuperCup races are held at F1 racetrack, where high speed turns are quite common.

All cars oversteer from a certain speed and up. Try running at 120 mph on straight line and start turning abruptly to see if the car will understeer , it won't. But the same maneuver at 20 mph will create massive push (understeer).

Bottom line, the timer is your friend, assuming the driver is extracting everything there is to the car, different springs will bring different lap times.

I personally like a car a little lose at high speed, because I can crush on the tight stuff, and very few tracks have high speed turns here in U.S. If I lived in Europe with chances to run Silverstone, Spa, I would have to use a lot more front springs.

At Sebring (based on videos) a stiffer front than usual should work better, as there are transitions and high speeds turns (and bumps !!!), so the rear needs to stay checked.

The stock 07 GT3 RS shocks cannot handle the rebound with a 4-digit stiff spring. I tested 750/1000 in my GT3 RS (ex-mooty, post-tcsracing), the cars felt like a ping-pong ball, bouncing up and down everywhere, the problem was shocks, not springs, when a car bounces up and down you get low/high grip, inconsistency on the turns, horrible driving feeling.

Let's see Erik testing my recommended spring rate next (450/750), he will like it better than stock, and his Orbit stuff.

BTW, I have the spring rates from the Manthey KW suspension for the 997.1 GT3 RS, huge split front and rear.

Now, If Erik keeps the rear 305 RA-1 and runs a 275 Ra-1 front with a 10"wheel, the stiffer front springs should help.

 

This is a great thread and am really enjoying it. I just have a lowly 09 Carrera S with the lower factory Sport PASM and always wondered if my car with stock shocks could benefit with a spring that is just a little stiffer. My car seems to lean over a lot in the turns.