ZX3tuning

So i guess the title is pretty self-explanatory but i have a line on some RSR coilovers for my 88 930 cab, only thing is they do not come with springs. I was wondering if the guys running something similar, what would be a good spring rate for a 80-90% street driven car?
Helper springs?

The car will see the track once in the while in the form of HPDEs and maybe the odd open lapping day with maybe one or 2 PCA AutoX's per year.

along with this i am looking for a sway bar upgrade, upper strut mounts and a strut brace to round out the suspension while i'm in there.

i'll be using the factory torsion tube arms as LCAs with the correct LBJs for the RSR struts in the front and will have a set of 935 spring plates in the rear and will monoball the inner joint on the banana arm.
the fronts will be a bit of a compromise but i don't see the need to get into the 935 front suspension until i grow out of what i have planned. i am not looking for a ***** to the wall setup, just something that brings the car into the modern era for suspension and will ne nice to drive on the street.


so to recap, spring rates for an 88 930 cab that is street driven with a nice set of sway bars.

the car will be spending some serious time on the scales and rack once everything is in, don't worry!

Thanks in advance

911rudy

I have the RSR coil overs on my car and they came as a set. Bilstein has the springs or at least the part numbers from Porsche.

ZX3tuning

and?

jimculp

I pulled my torsion bars and did coilovers with 600 lb front springs and 800 lb rears. I love the ride/handling compromise myself. Most people who ride in the car find it "stiff as a board" and my mechanic with a built turbo of his own found the ride to be too firm. It depends on what you are looking for. If you want a nice around town ride while having reasonable firmness for the track, I'd consider 500/700 or maybe 450/650.

I'm not sure how to calculate the pounds with helper springs.

My next addition will be adjustable sways- those will have a significant impact on suspension performance regardless of spring rate.

Whatever rates you choose, make sure to get your dampers re-valved to match.

strudel

The Smart Racing site specs out 450lb fronts & 600 lb. rears, and 23mm sway bars front & rear. Also their F10 street re valving. I would go with the Wevo strut mount/brace kit. For a better ride and handling I would go with the Wevo/Ohlins adjustable rear shocks. The shocks work with either coil overs or torsion bars.
If it's a street car with sometime track use I don't see a benefit of converting the back to coil overs unless you already have the motor out to gusset the rear shock towers.
The two race shops I deal with prefer a softer suspension set up for a good ride with thick sway bars do deal with cornering. If the suspension is too stiff not only do you get a lousy ride you also loose adhesion through the corners because the tires are skipping over the dips.
I would suggest you call them for more info.

jimculp

I've heard the rear gussets are required for track work and I've heard that the factory mounts are more than stout enough for the extra pounding. YMMV.

I have yet to see evidence of mount cracking due to coilover use.

ZX3tuning

It takes me 3-4hours to re&re the engine and trans so if i need to reinforce the towers that's not that big of a deal.

i'm reading and hearing a lot in the 400-500 range up front and 500-650 in the rear.
obviously this is going to be a very street dominant setup but i'd like it to be firm enough that it can still react to my inputs if it breaks loose or starts to get away from me on the track.... part of the reason why i'm going away from the Torsion bars. I'm building this car with my dad, and he drives it as well and it needs to be pretty forgiving so he doesn't get in over his head with the power it will have in the coming years.

keep in mind it's a Cab so it's not nearly as stiff as a coupe. the car does have a dasport roll bar but i question how much rigidity that will add considering it's only 2x 8mm bolts and 2x 10mm bolts holding it to the car.

also, using sway bars to do the bulk of the handling has always been a bad idea in my mind. it just masks a problem in the suspension setup. i've always used sway bars to fine tune the handling after the spring rates and shocks have been dialed in.... unless i'm trying to induce a aggressive handling trait not possible with spring/shock tuning.


i definitely think 600/800s is way to much for this car...

anyone played around with a Cab on coilovers?

nathanUK '81 930 G50

I know Stephen Kaspar had co's on his wifes targa. I would contact him about it all.

JBL930

I'm in the middle of this myself at the moment, i originally got the kit from IA but i've been dealing directly with Clint from Rebel Racing for the rest of the stuff, he's a really helpful guy.
I'm not entirely sure what my spring rates are but i'm going the same route as Jim, i'm scrapping the torsion bars all together and i'm told it'll be fine unless i'm doing really heavy track work.
Clint tells me that if i want stiffer than what i've got, basically to become more track focused, then the next step is 350/500. So i must be softer than this now and i'm led to believe this will be good for mainly road use. I can't imagine what 600/800 must be like Jim, do you have any teeth left? What does the car handle like? I would have thought it would be difficult being that stiff, i bet there is no squat but does it loose grip all the time?

As well as the front and back coil overs I'm also going with
Rear drop links and bushings
Hollow front sway bar, drop links etc
Triangulated front strut bar
Rigid upper strut mounts

When it's all fitted and ready i'll report back for you, i've no idea what it'll be like, i want less squat than when i have the stock torsion bars with yellow HD's, i may need to go a bit stiffer, we will see

PorscheDoc

Normally we used 300/400lb springs in the coupes, and 400/500 on the cabs for street applications, no torsion bars. I think Stephen ran 300/400 on the coilovers i put in his wife's targa, but that car is long gone to a new owner. Anything harder than that and you start beating yourself up on the street. I run 500/650 on my 951, which is very harsh on the street. You really have to watch for cracks in road and potholes.

jrottn

I bought a used set of RSR coilovers several years ago to use on a narrowbody targa. They came with 350/550 springs which seemed a good compromise for street track. The ride was good but yet stiff enough ( with big sways ) for track use. At the other end of the spectrum there is a 935 replica for sale that has run some sick times that runs 550/900 ( track only )
john
930rs

ZX3tuning

i'm curious to know why you'd run stiffer springs in a cab than a coupe considering how much softer it is than the coupe.

jimculp

I would guess that the inherent lack of torsional stiffness of the chassis would require stiffer springs to get an equivalent ride with a coupe with softer springs, but that's just a guess.

ZX3- I really like the ride with 600/800 springs and I don't have an issue with bump-skipping or anything like that- just lot's of grip. I have a friend with a 996 GT3 and while the ride is a bit firmer than that car, it's not appreciably more uncomfortable. I also run 17's, not 18's- 18's might be too much with my setup.

With my setup I don't see any performance deficit, but like I said people do comment on the firmness of the ride.

strudel

PorscheDoc thanks for the info. I'm getting ready to convert the front to coil overs and the rear to coil over tender/helper.

Jimculp: what shocks are you running?

jimculp

Spring-matched Bilsteins.