alexl911

I'm having some handling issues and I'm hoping I can get some advice here before paying for yet another geo...

This question is mainly directed to those who have made significant upgrades to their suspension set-ups and have experience with different settings and ride heights -especially KW V3/CS at RS ride height. I would really like to hear feedback from those how have driven an RS (lucky you)! I'm certainly no expert at suspension set-up so I've been going through this process to learn more. I've been relying on (who I believe to be) Porsche experts here in Germany but I believe that since my German is not great, there may also be some things 'lost in translation'.

So, over the past year I've been slowly turning my '96 993C2 into a track biased car -but one I still want to drive on the road for long distances. I'm not so concerned about comfort (I can live with the noise, vibration, etc.) but I am concerned about keeping some basic (safe) road handling characteristics. This past summer I have done the following upgrades in various stages:

-KW V3 Club Sport coilovers (later upgraded from V3 by the KW factory)
-KW solid top mounts (front & rear)
-RS front hubs (wheel carriers)
-RS sway bars/ARBs (front & rear) + FDM custom rear droplinks + Tarret front drop links (Set at the 'middle' hole)
-Wevo Engine Mounts (Black Pillows)
-ERP sport hardness front A-arm bushings
-Rennline solid subframe bushings
-18" MY02 wheels with PS2 N3 Tires

My ride height is at RS sepc. (I think as my Geo readouts are all in German) Since I've been doing the upgrades in stages, I have not yet tackled the rear suspension other than the new dampers/springs. The rear has the original bushes and ball joints. Also, the front still has the original ball joints. My mechanics have said that they all looked 'fine'.

Basically, I'm not happy with the high speed handling (i.e. over 200kmph - I live in Germany by the way so it's legal and I do it often). The car feels very nervous and bounces around. I really can't take it over 220kmph for fear of launching off the road! The car is all over the place with far too much lateral movement, passive steering, wayward crawling/squirming over undulations and uneven surfaces. At 200kmph on anything other than a very flat road it feels downright dangerous. I think I can could now drive my BMW wagon quicker on 90% of roads! In corners though it feels incredibly planted with amazing amounts of grip. BTW, I have about 1.5degree negative camber on front.

Tires pressures are perfect (I have a live Tire Pressure Monitoring System).

When I first installed the KW V3 suspension, I had the car geo'd and corner balanced an Manthey Racing. Since then I have removed the stock seats and replaced them with RS seats. Could that weight difference have made enough of a difference??? The V3 suspension was later upgraded to Club Sport at the KW factory and they did the Geo again (but before I had the RS bars installed).

What's interesting is that the biggest affect has been installing the Wevo engine mounts. I was never able to spin my rear tires but now I can easily do this!

Are there things that I can try before taking it the shop? I have not changed any of the rebound settings for ride height. I'm thinking that with all the changes and subsequent alignments something has gone off. I have never driven an RS but I can't imagine the ride could be so bad at high speed???

I doubt the problem is aerodynamic as my friend with a 993 cab can cruise at 270kmph on the autobahn.

The Jackel (over on 911uk.com) has recently given up on his KW V3 set-up and installed Bilstein PSS10's as he was not able to dial-out the same sort of issues that I have. His initial feedback has been that the PSS10's are a HUGE improvement.

Please guys -lets not debate the various merits of KW vs Bilstein here!! Honestly, I can't believe that my issues cannot be solved and ripping it all out and starting over is simply not an option. I need to work with what I now have.

Thanks!!!

DanQ

Not sure I can help, but it might be helpful if you could give the alignment settings and shock settings.

Sounds like maybe too much front toe out, and too little rebound on shocks but this is really nothing more than a guess with the info provided.

With the wheels on the ground, if you press your knee into the sidewall of the tire can you detect any movement?

trophy

I am running KW Clubsports with Camber Plates etc, TRG Sway bars, so should be able to help you out. I moved from Bilsteins to the KW's and found almost 2 seconds a lap (around a course of 1:28 ish lap time) I have found my setup to be excellent, good stability, great turn in etc.

Don't forget the alignment that will make the car a joy around the racetrack is going to be quite different to one that provides stability on long autobahn runs, If you are wanting both you may need to be making changes on a regular basis ie. Reducing camber for those high speed runs on the autobahn.

Really need some more information as DanQ alluded to:

- Alignment Specs front and Rear (Toe, Camber, Castor)
- Shock Settings (Comp and Rebound, Front and Rear)
- Tire pressures and tires

Are you running the stock springs that come with the V3 or did you upgrade to the liner rate springs of the Clubsport?

I know more questions than answers at the moment, we just need more information to make recommendations....

Some of your issues may be around the stiffness balance between the front and rear of the car, you have made more changes to the front than the rear. If your front end is responding quickly to steering input and the rear has to compress the rubber to then "catch up" can appear like the back end is moving around. Just some speculation, however really need the above information to create a more informed solution.

Bill Verburg

If you haven't replaced all the rear bushes w/ RS or hard rubber or monoballs that may be an issue

the stock rear toe links are terrible for performance toe changes particularly w/ soft springs can be dramatic, i'd want monoball toe links

lastly alignment and corner balance will have a huge effect on how the car behaves

alexl911

Bill - no I've not replaced anything on the rear (yet). I plan on going for original RS control arms rather than just changing the bushings just as you have done.

BTW - I remember that you once listed all the RS part numbers that one requires. Could you post them again here??

Trophy -I'm running the Club Sport springs. I will post the specs later when I get a chance however, I don't know if I have the shock settings -just the alignment and corner balance.

Bill Verburg

RS rear parts the only addition I'd recommend is the Tarret or Rennline mono-ball toe links w/ locks

when the rear alignment is off a 993 is a handful at speed, the rubber bushes don't help at all and you really ought to have both ends done the same way.

cgfen

i believe that the most likely cause of this behavior is a fundamental error in alignment (geo?).
It is possible that during the aftermarket bit installations something went badly wrong.

Please consider taking your car to either a;

local expert to drive and provide an opinion
or
to a different alignment shop to have the geometry checked / verified / reset.

other (unlikely) possibilities include
bad tire
bad wheel
steering rack issue
massively oversprung spring rates.

good luck in trying to determine if the problem is caused by the front or the rear of the chassis.

Craig

TheOtherEric

I believe that incorrectly spec'd spring rates would likely cause some weird handling behavior at high speeds. Vehicle Dynamics 101 says to set the spring rates in the front and rear such that the natural frequency (in a single-mass or two-mass model) is equal. In other words, if you put 400 lb/in springs on the front and rear of a 911, your car will feel really odd as the front & rear bounce at different frequencies going down the road. So check the spring rates.

I worked out the math on how much stiffer the rear should be, but I don't remember offhand. Something like 50% higher is probably about right, but I'd have to check.

JPS

Vote for alignment.

mcipseric

i would start with resetting the kw v3 setting. dial them all the way up then reset your setting. test. then check your geo.

vincer77

Is this a good thing?

Stealth 993

What are you suspension settings?
How much toe F/R
How much cater?

If you have toe out it will feel like that, but turn in great, sam for caster, you want to run as much caster as you can get. I would also suggest 0 toe.

alexl911

Thanks for all your input... I'm currently trying to translate my Suspension and Alignment specs from German to English so I can post them here (and I'm not a native German speaker). I'm also waiting to hear back from the guys at KW in Germany to get the spring rates. (As always t trying to juggle work and family at the same time).

Perhaps you can help me by telling me what are the key figures? I've had four alignments and one corner balance in the last two years and all of them seem to have slightly different readouts.

Thanks.

jackal2513

with that spec you have poor road manners for life .. regardless of what you do to the geo and regardless of all the undreds of permutations you can run the KW bump and rebound at

its an old car and it can't do what modern cars can do .... If you stiffen everything up and run large rims, thick bars, and lower it and remove every bit of rubber then over anything other than a totally flat road it will be pretty horrendous.

introduce some give back into the mix .... start by running some softer springs


IMO / IME

alexl911

Well here's an update:

I've now moved to the UK (SW London) and took the opportunity to have the geometry done (again!) but Chris at Center Gravity. For those not in the U.K., Chris comes highly recommended and has according to him set-up "..over 100 993's".

We'll I spent over 12hrs at his shop and he checked and adjusted every single suspension setting. Incredibly, it turns out that there were things that had never been touched, including the Kinematic toe!! Previously I had the geo and corner balance done four times (one of them a highly regarded, world class shop and another at the KW headquarters in Germany) and none of them had bothered to check the KT or the rake.

The end result -incredible! I have set the car up for part-time track use and spirited, fun road driving. Now, I have to humbly disagree with the "jackel" as my road manners are now very good (even with the shockingly poor roads around London) and I invite him to take a test drive anytime. Don't get me wrong -the car does not drive like my E61 BMW. It's a bit rough, a bit harsh and communicates everything in the road but that's exactly what I wanted. It's what I would call a 993 'Club Sport' -NOT an RS. Mind you it's not there yet -I'm still planning an RS clutch, brake cooling and some harder rubber rear bushings.

I drove it at the Donington circuit yesterday and the consensus by me and a couple of others; one of them a previous owner of a 993 with KW CS suspension and the two other instructors; was that the car handled excellent but could be even stiffer. However, as I'm a novice track driver they said it was fine for now.