Suspension Change...

[OllieW]

The dampers and springs are getting a little tired on my car as they are the original ones fitted in 1992 when it was made, so time has come to change them.

I am looking at the KW Coilover kit for the 964RS as this looks like a good solution from both a quality and cost point of view.

Does anyone have any experience of this or can recommend another kit to consider.

Thanks

Ollie

 

[Yoda]

A friend has recently had the PSS9 kit fitted to his 993RS but has yet to use the car. The guys who fitted it said it was a good solution for the 964RS, excellent on track and slightly better on road. Might be worth looking in to. No idea of cost etc.

Regards

 

[clubsport]

Dunno where Lemon yella Laurence is,,,but I yhink he fitted new KW shocks on his RS, it seemed to track well enough...hopefully he will be along soon!

 

[Laurence Gibbs]

Yes i have the full variant 3 KW kit on my car and i'm very pleased with it. Car was a pleasure to drive at Spa and my data logger tells me i'm a bit quicker at Brands too. The car is more compliant on the road soaking up the bumps better but still feels like an RS. It's still very much in shakedown mode at the moment as there is an awful lot to learn about it. It's basically the way the factory went with the 3.8 RS and could be viewed as a natural progression.
The standard supension though is pretty good and it's a fair bit cheaper to go that route. If you do I have a set of brand new RS springs from Porsche that I bought and then went the whole hog and bought the KW kit. I want about £250 for them (i paid £320) , The KW kit is availible direct from KW via there GB arm. You could also get it from some of the Porsche specialists like 9miester. cost is as per there website from KW don't know what Colin sells them for.

 

[SimonExtreme]

I have looked at various options and am not convinced either way - staying standard or going for something like the KW kit. I take on board that the KW stuff is more compliant on the road and has lots of adjustment but I am not convinced that, for me, it is actually better for track work. I am sure it will make it easier to be quicker than the standard suspension but suspect that the problem with the standard suspension is exactly what I like about it. The car feels and reacts like a race car (no suprise there!) and that the sharpness and ultimate edgyness is what does it for me. I think that the KW set up would end up as too much of a comprimise for me but then, I am mad enough to think the standard suspension is OK for everyday driving.

If I were doing more trackdays and less road miles, I would be looking for stiffer settings as I can feel and have seen in photos of me driving the car, more body roll than I would ideally like. However, the standard set up is still the best standard set up I have ever come across on a car sold for street use (save for the odd Caterham!).

So, where does that leave things. Well, if you are looking for a more compliant ride without losing too much of that special "RS" feel, the KW set up might be for you. You should, however, try to get a drive in both and if its a car with standard suspension, make sure its new because the difference between good and bad is unbelievable!

 

[clubsport]

Simon, surely with the adjustment on the KW you could have it at standard stiffness for the road and even stiffer on track to prevent body roll,,,ok roll bar settings may need a tweak, if you are not on max stiffness now,,,,,,,how bad would that be??

 

[Laurence Gibbs]

Simon i think you are making the assumption that a compliant suspension can't also feel stiff. Notice i was careful to say more compliant rather than softer. The big bonus of the kw setup is it absorbs the bumps better, meaning the tyres stay in contact with the road more often, giving greater grip; My car does not feel noticibly softer!
As i said in my first post there is nothing wrong with the standard set up it's very very good. I just view the more modern twin spring setup as technologically superior to the standard set up. Porsche did exactly what i have done with the 3.8 RS and i'm prepared to accept that they had good reason. You could go stiffer using the motorsports suspension and linear springs but this makes the car far less useable on the road and really needs the added stiffness of a roll cage to get best use from. It also involves swapping out you top mounts which adds to the cost. The standard twin tube front shocks are not rebuildable so fitting stiffer springs to these without revalving is a waste of money.

 

[SimonExtreme]

ORIGINAL: Laurence Gibbs

Simon i think you are making the assumption that a compliant suspension can't also feel stiff. Notice i was careful to say more compliant rather than softer. The big bonus of the kw setup is it absorbs the bumps better, meaning the tyres stay in contact with the road more often, giving greater grip; My car does not feel noticibly softer!

Larence

I don';t believe the physics add up! Compliant means it gives more and to do that, it needs to be softer. I cannot see how it could be any other way.

I am uncertain as t6o how you are making your comparisons because surely your old times were on suspension that was totally shagged. The speed differences between tired and good suspension at somewhere like Brands is 5-6 seconds. I know I can gain 2 seconds there just adjusting good suspension (on a race Capri!)

I am not saying the KW suspension is bad. In fact, for certain purposes I would have thought it was fantastic. But, I suspect that the standard suspension would be faster around a track and if I were looking for faster times on the track, the suspension would be significantly less compliant!

The comments about the 3.8 suspension have validity BUT it must be remembered that the changes were in response to the critisism that the 3.6 suspension was just too extreme.

You choose the suspension to suit the type of driving and the experience you are after. For some, that means a more road orientated set up while for others, a more track focused set up is for them. I personally believe that despite what manufacturers might like us to believe, you cannot have both.

 

[paul howells]

Hi simon
You can have both,with modern dampers.Such as JRZ,moton etc
Saying that,i had JRZ tripple adjustables all round on standard 993rs springs,very good,especially in the wet.These dampers helped my competition times in the wet,but not in the dry.
I have since junked the £4k dampers and fitted standard back on,with a better geo set up and now faster than the jrz dampers on lap times and the first 64 feet standing starts.(This is on standard springs)
I then fitted the JRZ dampers to the gt2 racer,and they out performed the bilstein tripple adjustables big time.
I think standard is best,you can get used to how the car feels all the time,ie the same,which also helps.
The double springs ,3.8 rsr,gt2 etc have considerably stiffer springs in general,and have adjustable dampers to match/control the springs.And of course stiff is not always best!!
ie spa and the ring.As a example for spa with my gt2 race car,i fitted 2,000lb rear springs and 1800lb front springs,it then took me nearly 2 days to get the dampers to match the springs!!with the adjustable dampers.But then try driving around the ring on such springs!
The real advantage of adjustable dampers is also to increase the nitrogeon gas pressure in the remotes,which will then actually help support the car,as if putting stiffer springs on.
And in the wet,drop some pressure out,as if fitting softer springs,which allows the car to roll more for wet traction.

Its a science for sure.

 

[SimonExtreme]

Paul

Everything you say makes sense but you are talking about dampers and I totally agree that dampers make a big difference. That is where I would spend the money.

However, what Laurence and Ollie are talking about have, I believe, less stiff springs than standard and while I am sure that this will make the car nicer on the road and easier to drive on the track, it will not, ultimately be as quick as the standard set up (on most tracks). I don't think that the standard gear is too bad at all but having now had a chance to analyse the tracktime I have had, if I were track racing I would definitely be uprating dampers and fitting higher rated springs.

Sprints and more particularly, hillclimbs, need slightly different thinking due to the start, cold tyres and the nature of the courses. However, you already know that and have far more experience than I do in such matters.

One point of interest for me is that you are running standard springs on the 993rs. Have you stripped much weight out of the car? Weight of car vs spring rate makes a huge difference. I remember when Steve Soper drove a Fiat X19 for Radbourne racing and spent the first 3 meetings going very fast and then even faster into the scienery! They had bought the car from Italy, removed 150kgs that the UK series allowed but didn't change the springs! The car was undrivable! Softer springs turned it into a winner.

 

[Laurence Gibbs]

Simon
I am not going to try to explain the workings of a modern twin spring adjustable suspension. I can only relay what I feel. The car feels as stiff (ie.has the same amount of body roll etc) but handles bumps better.Compliant for me means the car follows and handle the bumps better, the fact that one spring is susbstanially lower in rate means it can react and follow the bump and return and settle in a way that the standard spring can't match. It feels better on circuit and on road.It may be softer (i don't know exactly) but i'd defy you to actually notice it!! The twining of the springs allow for individual spring rates to be lower, however you have have to take both springs into account when calculating actual spring rates and the science is quite complex.As is the way the springs work together. The dampers are also adjustable giving quite a lot of scope for tuning(from silverstone to the nurburgring and the M25). I did try a vague comparison with another RS with known good suspension and I drove both my car and the other at brands and my car was slightly quicker. There was not a great deal in it either way to be ultimately fair. But i think we were talking about a replacement for standard suspension, not a set up to go racing! Therefore i think the KW setup offers an improvement in all areas (not just on track) and offers a good upgrade path. But it's not for everyone.
If one decides to go for stiffer springs and matching dampers then the best £/£ route is Bilstein hd's matched to linear rate springs and motorsport top uniballs. Doing this however will vastly effect the on road useabilty, you will certainly be faster at some tracks but possibly slower at others. If you want the car to stay together the fittment of full roll cage is also usefull.

 

[paul howells]

Hi simon
64rs springs are not that stiff realy,what makes them less compliant on the road is also the solid top mounts,and stiffer rubber bushes on the bottom wishbones.It is mainly the front end that does not work so well standard,the rear end is awesome!
Some people have changed the bottom wishbones for slightly softer rubber,just to make them a little more forgiving on the road.!
KW is not just about springs,the dampers are well matched to do the job and not mass production units,if you know what i mean.(they are good value for what you get)
You can run stiffer springs,but the important part is getting the damper to control the spring and get the wheel back on the tarmac and stay their for each bump.

The springs on my car well suit the weight of the car,and match the rest of the suspension,even the nylon wishbone bushes!The springs and dampers are Still a little soft for v fast circuits .Its been a lot of trial and error,as most calculations and computer programmes did not work for me and my car.
For circuit use,think about the 993cup dampers and springs,not adjustable,but fantastic on the fast circuits as well as the slower circuits.But they are almost dangerous on the road!
Any of you guys at silverstone on thursday.

 

[Laurence Gibbs]

Here is a picture or the 3.8 RSR suspension.

 

[chfs911]

I have the H&R dual spring setup by PSI Motorsport. They are similar to the RSR pictured.

PSI motorsport Porsche Tuning Reportages

Suspension Sport H&R
(double ressorts RSR)

#PSI-64-SU-1

2.850,- Euro /B

 

[SimonExtreme]

Having had time to do my homeworks..........

Paul. I am suprised that you didn't stick with the JRZ triples on the 993. They seem to me to be close to ideal. Logic says that there must be a combination of settings that make them perform the same as the standard set up in the dry and it is clear you found a better set up in the wet.

I would have thought that the JRZ set up would be particularly good for a fast road/track compromise as you can adjust the low speed daming and mid/high speed seperately. It should also have an advantage over the KW set up because the seperate resevoir. But it does seem expensive. I do think it would give a better set up, using standard springs, than the dual spring KW set up and despite what Laurence might say, dual springs lead to more initial roll.

Dual springs have a lighter initial spring rate which provides for a smooth, supple ride oversmall surface irregularities. Then, at a detrmined point in the suspension travel, the stiffer spring takes over. Spring rates are very simple. They are measured and it is a simple fact that a lighter spring rate leads to more body roll and therefore if a dual spring suspension set up has an initial spring rate lower than standard, the car will, initially, roll more than a standard car. What complicates matters is the ability to adjust damping and in particular, low speed damping.

Bottom line is, having now amde the enquiries, I am totally convinced that initial body roll with the KW set up is more than with standard springs. However, total body roll may be the same or even less. However, the initial extra body roll will effect the turn in characteristics. I fail to see how this can lead to faster times on the track.

I really fancy some JRZ or similar, but don't know if I can really justify the expense[]

 

[paul howells]

simon
The jrz i fitted to my gt2 racer,they are great,when you have time to set them up.
Also you realy need to understand them,otherwise your times go backwards.Its not just a case of twiddling the knobs,the main indicator being time.

I have just worked with a friend on his 964 rs,new wishbones,new standard dampers allround,wheel bearings,good tyres,and most importantly a good set up.The car will stay with any 964rs and damper set up!
He could not believe how the car feeds back the feeling/of more grip dialing in as you turn in.A good set up should encourage confidence in the corner,not oh shit!!

Double springs,depends which type of dampers and springs you refer to, for initial body roll.My gt2racer there was none,the little springs are basicaly there to keep the big spring in place on there perches,when the damper/springs load and unload.
Properly set up,to match your car etc,you should have less roll.

 

[SimonExtreme]

ORIGINAL: paul howells

simon
The jrz i fitted to my gt2 racer,they are great,when you have time to set them up.
Also you realy need to understand them,otherwise your times go backwards.Its not just a case of twiddling the knobs,the main indicator being time.

I have just worked with a friend on his 964 rs,new wishbones,new standard dampers allround,wheel bearings,good tyres,and most importantly a good set up.The car will stay with any 964rs and damper set up!
He could not believe how the car feeds back the feeling/of more grip dialing in as you turn in.A good set up should encourage confidence in the corner,not oh shit!!

Paul

I think I have been spoiled! Less than 2000 miles before I bought my car, it had all new wishbones, bushes, springs, dampers, mounts etc. In fact, everything in the suspension department. And the geometry was (and I hope still is!) well set up. I have also driven cars with tired suspension and those do give you the OMG feel. And that has been my whole arguement. The standard set up is pretty good indeed and I really do question the need for dual spring set ups on the '64 RS.

I also accept what you say about time to set the JZR triple adjustables.

My gt2racer there was none,the little springs are basicaly there to keep the big spring in place on there perches,when the damper/springs load and unload.
Properly set up,to match your car etc,you should have less roll.

Agreed on a race set up. But the KW isn't a race set up and the comments I made where their own.