I did a bunch of suspension work to my 997.2 C2S and am noticing a very noticeable handling change that I did not expect so wanted to post in here and see if this is something you have seen/experienced as well or if it's something I need to keep trying to sort-out. I could learn to get used to it and I wouldn't say it's necessarily a BAD thing but it's definitely pronounced and new.

I went from all stock suspension to Ohlins R&T coilovers and lowered the car about 15mm front and rear (preserving factory rake numbers), GT3 front and rear swaybars with adjustable drop-links set to ensure no pre-load and the bars adjusted to the OEM recommended holes, GT3 front LCAs shimmed out to give me camber, SPL rear bump steer adjustable toe links which I adjusted via a bump-steer gauge to ensure minimum possible rear toe change throughout the full suspension range of motion (I am now getting only -.05" of toe-in at 2" of compression).

Alignment is - Front: -2.0 camber, 0 toe, and probably 8.5-9.0 caster. Rear: -1.5 camber, and 4mm of total static toe-in (2mm per side).

The change in handling that I'm noticing and not sure that I like is that mid-corner, if I lift off the gas at all, the car wants to pull into the turn. The effect is quite pronounced. I could understand this if I was talking strictly about driving 8 10ths on a track and drifting a bit mid corner because lifting would put more weight on the front tires and cause it to bite into the turn more, and I also understand that on these rear-engine cars, having all that weight out back can cause rotation as weight is transferred from the rear tires to the front, but the issue is that I'm noticing this under low speed normal driving, not track driving. So if I'm driving down a two lane country road at say 45mph and there is a gentle sweeper, the kind that you could take a lot faster and don't even need to slow down for to make it comfortable for your grandmother in the passenger seat, if I go from whatever throttle position I was at to maintain 45mph and I lift off the gas and keep the steering wheel in exactly the same position that was previously maintaining my turn angle, the car will turn-in to the turn to the point where if I don't make a minor steering correction in the opposite direction of the turn, the car would be turning-in too sharply for the turn. There is no slipping of the front or rear tires at this speed. The car also feels a bit nervous under heavy braking at high speeds.

To me it just feels unstable and the car didn't do that before these suspension mods. I haven't played with disconnecting or adjusting the sway bars to see if they are causing or contributing to this, and that's my next step, but before I spend a lot more time on this (I was certain the bump steer adjustment to the rear I spent two full days doing would fix it but it did not), I thought I'd post here and see if anyone had any input. If this is just how these cars handle when you stiffen them up, I could accept that and learn to adapt my driving style to it, but I'd like to be sure something isn't wrong first.

Thanks in advance

 

1. Spring rate?

2. "OEM" sway bar position without knowing your spring rates is.... guessing at best.

3. Trust you did the whole alignment yourself and are confident about the numbers.

4. Lift-off oversteer is generally desirable but the amount you're getting may not be to taste.

5. Easiest adjustment would be to take some rear bar out. Remember you can adjust by one hole on just one side for fine adjustments (remember to adjust drop link length if asymmetrical bar holes).

6. More rear toe-in (not desirable).

7. More front toe-in (not desirable).

8. Less rake (always worth playing with). Remember for adjustments more than one full turn you will probably have to re-adjust toe, depending where you are on the bump curve.

9. More front compression.

10. More rear rebound.

11. Check for any evidence of binding (witness marks).

Adjust one variable at a time and make notes. Getting access to a skid pad for half a day is a great way to set up preferred balance.

 

Doesn't sound normal. Check the work on the suspension, tire pressures ect... basic stuff first.

 

Thank you for the reply!
1. Spring rates on the Ohlins are 336 front and 672 rear (lbs/inch)
2. Front sway bar is 1 up from full loose, and rear sway bar is one down from full stiff
3. Yes I did the alignment myself using a smart strings setup with a digital angle gauge for the camber. 98% confident in it. The last time I took it to the shop to get aligned on a Hunter rack, my alignment settings were right on the money.
4. RE lift-off oversteer being desirable, would this statement apply even when there isn't any tire-slipping taking place? My assumption was no, and that's a big part of why this is bugging me. I don't feel like I should have to counter-steer when lifting off while driving at 1/10th as in normal day to day street driving.
5. Rear bar adjustment - yeah I think I might just disconnect the rear bar completely as a test to see if there is any impact at all and if so, I can adjust it from there, and if not, I can start looking elsewhere
8. Less rake - ok I will look at this thank you
11. Can you elaborate on how I'd check binding? I haven't heard of witness marks before.

Funny you mention the skidpad - I have a skidpad/slalom session booked in February. Was hoping to get this issue ironed out first since I won't be able to work on the car at the track.

@coryf thank you for the reply. I've checked everything since I did the suspension work myself. All is rock solid and tight. Tire pressures are right.

The only other thought I had was that I read an article about this intentional movement in the rear suspension bushings designed in by Porsche:
https://www.total911.com/technology-...h-effect-axle/

The TL;DR version is that Porsche designed the LCA bushings to have a different amount of compliance vs the rear toe-link bushings. The engineers designed it like this to ensure a rear toe-in condition under suspension loading instead of a toe-out condition (and this is different from toe change under compression - this is strictly in response to loading under a corner, which goes above and beyond whatever you are going to get from the toe changes caused by suspension geometry). I read two articles on it and IIRC each article contradicted the other about which was the softer vs harder bushing (IE softer on the LCA or softer on the toe-link), and I don't really know which direction the car would toe under bushing loading if the bushings had the same compliance. I bought and installed bump-steer adjustable rear toe-links for two reasons: The first is that I lowered the car and wanted to be able to adjust out as much bump steer as I could, and the second was because Tarett Engineering highly recommended installing aftermarket rear toe links specifically because they said the rubber inner bushing of the OEM toe-link is very compliant and causes toe changes under load (the aftermarket versions replace that rubber bushing with a monoball rod-end). Now my fear is that you might WANT that compliance in the rear toe link to ensure you are getting toe-in (or no toe change) instead of toe-out when the suspension is loaded up and the other bushings start to compress. I would have to re-install the OEM rear toe-links and do another alignment to rule this out.

 

One more question:

You mentioned minimal rear bump steer in compression. Did you check for toe loss in droop?

 

Hah I just replied to your reply at the same moment you just sent this - see post above for answers to your previous helpful post.

To answer your new question, yes I did and here is the chart showing what I got after adjustment - basically no toe change in droop, and 0.05" of toe change (per side) at 2" of compression.

 

^ ok, good.

Factory rear:front spring ratio is @1.7

You now have a ratio of 2.

Pull one drop link off the rear bar and go drive it. Report back.

 

Will do - Might take me a few days to get to it but I will do it and report back. If that fails, I feel like swapping the OEM rear toe-links back in is the next move (if the sway bars don't change anything), but that's a huge job sadly because I also installed a toe-link locking kit which replaces the eccentric bolt on the rear toe links with a regular bolt and locking plate (the eccentric doesn't have enough adjustment range to properly set rear toe when you lower the car much - which is another reason for the aftermarket rear toe links: they have a wider range of adjustment). The headers are in the way of getting that long bolt all the way out of the subframe so you have to pull the exhaust and headers to get it out. PITA.

 

I doubt your toe links are the problem.

 

I wouldn't bother with changing the toe-link. I agree with jdistefa. It sounds like the rear is stiffer than you'd prefer and the easiest (and likely most effective) thing to do is to soften the rear sway bar. Disconnecting one side will definitely tell you how much of a change it will make and then you can reconnect at a soften setting if you get too much understeer.

I'm the first to say that I don't enjoy making mechanical changes at the track, but honestly changing the swaybar setting is fairly simple and something that will allow you to adjust the handling based on your what you experience in a more realistic (not street) setting.

 

if its really that dramatic that you are countersteering going around turns at 1/10th, I'd really consider checking your alignment. Sounds like you got some rear toe out

 

A gentle sweeper at 45 mph in your car should be a total non-event. The fact that the car gets unsettled at that speed makes me wonder if something is loose or incorrectly installed.

 

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Got it thank you. I'll look for that. I definitely noticed no binding when I had the springs out of my coilovers to do the bump-steer checking and adjustment.... very smooth. But I'll check again.

@stownsen914 and @Quadcammer - I've torqued everything down to spec and double checked it all. Nothing. I agree it should be a non-event. I won't say it's scary or anything, but it's odd that it requires some steering input change with throttle lift (an easy 45mph turn on a freeway onramp might require me to back off about 10 degrees less of steering wheel position to maintain the exact turn radius if I lift off the throttle completely mid-turn with no tire slip). IMHO the only time steering correction should be required is with some amount of tire-slip.

 

Question about static rear toe-in. I'm running 4mm total (2mm per side), as measured from the outer lip of the wheel (19" wheels), not the tire contact surface. For those of you measuring toe in mm instead of degrees, is this about how much toe you are running and are you measuring it from the same place as me? I've done the math before to convert mm to degrees, minutes, seconds, etc, but it's a pain.