rs10

I’m wondering how much slightly stiffer anti-roll bars/stabilizers affect ride comfort. Would it be equivalent to going from the standard suspension to the sport suspension (M030, I think)? Or going from M030 to Bilsteins or Ohlins? Or to switching from 17s to 18s? Increasing the spring rate X%? (The anti-roll bars I have in mind are ~10% stiffer (I’d use the softest settings on the road).)

Of course, anti-roll bars only affect ride comfort in certain circumstances, which makes comparing their impact with that of stiffer springs or dampers or tires tricky. If they have the same overall impact on ride quality as, for example, the M030 suspension, it means sometimes thay have more impact and sometimes less.

Still, if anyone can share any insight into this, it would be greatly appreciated!

davidnyc

Good question. Theoretically if both wheels go up and down on the same bump (like a speed bump) there will be no difference. But in real life situations you will definitely feel "some" increased spring rate. The issue is converting your roll bar stiffness to the effective spring rate at the wheel. Have fun with the math on that one.

TonyTwoBags

I have a C2 with a stock suspension outside of H&R adjustable sways in the front & rear (medium setting). I've noticed substantially less body roll & had a blast during a track day. Have not noticed reduction in ride quality to date. The ride balance now is perfect for a canyon car though I may add more suspension goodies in the future.

David 23

I'm curious what specific spring rates people are using with coil overs to tighten the handling and control "floating". I have PSS9, and with the standard springs that came with the struts there is still a vague feeling, particularly with the front end. Looking for a crisp, tight, canyon/track oriented car that will still see street time.

DTMiller

I'd be very surprised if a change in rollbar stiffness -- alone -- was noticeable in street driving.

pavster

I have a 997 C2 and the only suspension mod is a GT3 rear sway bar, which is significantly stiffer than the stock one. Set to middle setting. Made the car much more neutral with easily controllable oversteer on both power and lift. Really fun. As far drivability, yes, it did increase 'busy-ness' over rough pavement. HOWEVER, the change from my stock Michelin PS2 to Bridgestone RE-11 tires was a more drastic change (for the worse) in terms of ride comfort.

mdsarch

I am confused. PSS9's are a coil over "system", as such you shouldn't be using your stock springs.

Slakker

Coilovers usually have a spring range that they are rated to operate within. IIRC, the KW v3s could be increased by 90lbs which wasn't enough to mess with.

But to your point, there is absolutely no reason to change spring rates on a coilover until you have maxed out their potential and are looking to solve a specific problem.

David 23

I'm using the springs that came with the PSS9s, not the stock Porsche springs. Sorry if that wasn't clear.

"But to your point, there is absolutely no reason to change spring rates on a coilover until you have maxed out their potential and are looking to solve a specific problem"

Slakker, I am trying to solve a specific problem. My experience with the PSS9s so far, is that with the shocks set at anything less than full hard, the car feels vague and floaty, not taut and crisp. My understanding is that I shouldn't have to correct this floatiness with excessive stiffness in the shocks but rather by finding a higher spring rate, and reducing the shock stiffness a bit, therefore controlling the float and still having a bit of shock compliance. I am very willing to be corrected if I have misunderstood the dynamics.

As for the OP's question about sway bars and ride, when I went to substantially stiffer bars on my previous 993, there was a very minor change in ride "stiffness", but I wouldn't consider the change a negative one.

OKB

if you use 030 spring or H&R etc it will be slightly firmer. 030 shocks will be harder. coilover system will be as hard as you can get. you probibly couldnt tell anything if you change the bars

rs10

Indeed. And I have, and I am.

rs10

I've spent a fair amount of time driving a PSS10 equipped 996.2, and I was super impressed by how much more direct and locked down the front felt. Still stiffer springs might make it even better, but I'm guessing there is something else going on. So let me share some thoughts. You probably know at least 90% of this, but maybe if I throw enough ideas out, one of them will be new.

First, as you probably know, PSS9 spring rates are almost the same as a GT3's, not a car known for vagueness. Not by 911 standards, anyway. I see in your signature that you've owned various 911s, so you know a light front that moves around a bit is part of the deal with so much weight in the rear. Still, for diagnostic purposes, you might try doing some test runs on a road you know well with an empty tank and no spare in the trunk, and then try again with a full tank and the spare.

If it is the weight distribution, it is possible to shift this a little bit. You can take out the rear seats, get a stainless steel exhaust (or inconel, titanium however seems to be unavailable), replace rear windows with some sort of plexiglas or similar, and get a carbon ducktail. Also, surprisingly, I think lighter front seats will also slightly shift the weight frontwards. So you can lose a little weight from the car - and a lot from your wallet.

Or you could simply slightly tilt the car forwards. Sounds like a bad idea to change the angle from what Porsche intended. But what you started with may not be exactly what Porsche intended. Not in the US, anyway. US cars sit 10mm higher in the front. So if you uniformly lowered all four corners with your PSS9s, then your car is still tilted up in the front compared to a RoW car. Lower your front or raise the rear an additional 10mm, and you will shift some weight forward. No idea how much. Furthermore, if you have stock 18" tires, switching to the optional 295s in the rear will give you a further 3mm tilt towards the front.

Tilting will also affect the aerodynamics, which may also play a role. It's at high speeds that our cars get particularly light in the front. There isn't that much lift, but the small reduction necessary to roughly cancel it is often said to make the car feel noticeably more stable. The aerokit will do it. So will a turbo bumper in the front and, I think, a turbo wing in the rear. Obviously it's the aero and turbo bumpers that address you concern with the front, but it's widely said to be a very bad idea, making the car unstable, not to make a matching change at the rear. (Possibly even worse is just doing the rear. A big enough (high quality) wing will generate some downforce, and this will actually increase lift in the front by pressing the car down in the rear and thus tilting it up in the front. That's on a GT3. On a carrera with a stock suspension, the effect will be a lot greater.)

There are also a number of basic potential fixes which are a lot cheaper than aero and weight distribution: Make sure your geometry is right, your tires have even tread wear and aren't too old, and your wheels are balanced. Replace all replaceable bushings. This can even include the engine and tranny mounts - all that weight sloshing about in the rear can make the front feel vague. And get more precise tires. Something like a PSS will be super precise, and a PS2 is pretty good, but some tires, especially some non N rated tires, will be noticeably vaguer. If you are running lower than stock pressure for more grip, you are sacrificing some precision. If you are running 17s you will also have less precision/more float.

Regarding geometry, "right" has several meanings. There are standard setups for the normal suspension, the M030, for a GT3, and, presumably, for X74. As you get sportier, you will get less front toe in and more front camber. These changes will make the car feel less stable when you are trying to go straight ahead, but provide quicker turn in and more grip in turns.

And finally, back to spring rates. The PSS9s are close to GT3 rates, but not the same. Both have 90 Nmm rear springs (I saw somewhere 95 for a GT3, but I think that's wrong/not a 996). But PSS9s have 45 fronts, whereas GT3s have 40s. Reducing your spring rate to 40 - definitely possible with PSS9s - should give you less understeer and quicker turn in.

For whatever reason (and if anyone knows, please share the answer!), the 996.2 is said to have slower turn in the than the 996.1, and this is true for both the Carrera and the GT3. Could be some of the above reasons - e.g. weight distribution, front/rear tilt, etc. Or something different entirely ... .

Of you could just get a C4S or a TT

Hope this helps!

David 23

RS10, thank you for all your effort to present such a thorough set of suggestions, I really do appreciate it. I can respond to some of it now, other parts i will need to get back home to the car and take some measurements etc.
Yes, I've had a number of air cooled 911s, including early and late, race car and street. The most precise handling 911 I have owned was a 96 C4S, with JIC coil overs with the heavier springs and RS bars, links etc. lots of the associated bits, and a serious track alignment camber and toe wise. This did include a substantial rake that I always felt added to the incredible stability of the car at speed or on undulating surfaces. These are exactly the conditions the 996 feels the most unstable. I've only had the 996 a few months, and haven't thoroughly measured the suspension settings the car came with, but I will indeed do that now. I think your mention of forward tilt (rake) is definitely worth examining further. As for aero, the 996 is a 40th AE, so it has the C4S front end (very much like the turbo) and it has the GT3 rear deck wing and rockers. So I suspect I am covered appropriately with the correct body panels aero-wise.
I had the shop (trusted high reputation race oriented shop) look over my suspension components for any problems while they had the car in the air (for IMS), and they didn't seem to find any glaring problems with bushings.

I think I'll start with measuring if I have any rake, and if so how much, then proceed to an appropriately aggressive alignment and corner balance, which from my experiences usually adds the correct rake to shift weight forward. At that time I can specifically examine bushings for wear and replace whatever is needed.

I'm always a little confused when trying to understand spring rates, as some are listed in Nmm as you have, and others (many aftermarket like Swift) list in lbs per inch (?). WHile doing a search on RL I found an old post about some higher rate PSS9 front springs specifically for reducing front end float. They were described as 348 lbs. but I don't know how that compares to GT3. Thank you again for your comments, they are most appreciated!

Slakker

The PSS9's have a front spring rates of 285F and 570R for the main springs. You can go up to about 325 on the front as is. Any more and you will want to send them in to Billstein to get them retuned. 375 is about as far as you want to go.

Take can definitely help some as well.

As far as visually inspecting a shock, this offer little value. The only way to tell if a shock is performing is with a shock dyno.

Ultimately though it sounds like you will eventually need to go with a PSS10 or KW V3 to get the balanced performance you are looking for.

David 23

Thanks Slakker, that is exactly the information I was looking for. It helps as a comparison to other systems. You may be right that a better solution would be to simply replace the entire PSS9 coil over system with something else a bit more aggressive/suitable. Is there much difference between the PSS9 and PSS10 systems? I always thought they were very close. I have heard good reports on the KW. Has anyone had experience with the Ohlins system?