Correcting rear suspension geometry on lowered Carrera

Hello everyone. I have read a number of threads on this topic across this and some other forums. There isn't a clear consensus on the best next step, so I have a couple of questions specific to my car that I hope you can help with. It's a high mileage 3.4 Carrera 2 which I bought knowing it needed some work. Part of this was a complete overhaul of the suspension. My primary concern is for road use, so instead of getting carried away with monoball-type arms and exotic geometry I made the decision pretty early to stick to OEM rubber-bushed parts everywhere. So everything is standard but new, apart from the rear upper control arms which are old but showed no signs of serious deterioration. Anti-roll bars are standard, dampers are Ohlins Road & Track with standard spring rates and set to whatever height the book said (circa -30mm I think), tyres are Pilot Sport 2. I love the way the car drives. The dampers make it remarkably capable and confidence-inspiring, I can get it to turn in where I want, it's fast, and it's comfortable. Could it be sharper? Yeah, sure. Do I want it to be? Not sure. Maybe not that bothered. I probably won't take it to the track but I might. Here's the thing: I spun it. I'm under absolutely no illusion that it wasn't entirely my fault, and a Swiss-cheese model of things went wrong that day that led to what happened. But, I'm careful and I like to think of myself as a pretty safe pair of hands that generally doesn't crash things, even when driving a bit too much like a nob. Nonetheless it caught me out, somewhere I didn't expect it to let go. I know what I did wrong, but I haven't been able to shake the thought that something doesn't feel right about the way it let go. It went too fast. As I've been working through the car repairing it and tending to some incidental work, I've been wondering if compromising the rear geometry by lowering the car was a factor. I was aware at the time that we might struggle to get the rear aligned, but we managed to get the toe within spec and so didn't worry too much about it. I was advised to keep an eye on the tyre wear and see how it went (for fear of disappearing into an American forum rabbit hole of very expensive parts). These are the alignment results: Camber -2*20' / -2*38' Toe +0*10' / +0*07' Here is the worse of the two rear tyres after 8k miles: It's not so easy to see, but there is an even taper across the whole width of the tread, which I attribute to the camber and I'm not too worried about. What is more concerning is the wear on the inside shoulder, which I would have assumed to be toe; especially if I hadn't just had everything renewed and the geometry reset. I can take a picture of the new tyre I have waiting to go on for comparison, but I suspect these wouldn't have gone much further before they were done. I have a good opportunity to replace some parts while the car is off the road, and whilst the price of Pilot Sports seems to go ever upward I'd rather not just keep throwing tyres at the problem. The European advice seems to be to first fit adjustable toe control arms in order to allow the camber to be brought back into spec with the factory eccentric adjustment on the lower control arm. The American advice however seems to be either to fit adjustable upper control arms to correct the camber in isolation, or to just throw $10k at Elephant Racing arms and build a cup car. Really, I'm trying to decide between: adjustable toe control arms with or without toe adjustment lock-out, as above with adjustable upper control arms, with or without camber adjustment lock-out. So, my questions: I know that -2* camber is well outside Porsche's spec, but would those of you more experienced in fast setups consider this too extreme for the road? It does get driven quite hard, but it also has to do quite a lot of motorway miles. Are the static toe angle values concerning, am I right to think that this wear pattern is caused by excessive toe, and if so is this likely to be caused by the kinematics going to ***** because it's now lower than it should be during a static alignment? Is option 1 above enough / are the frustratingly expensive lock-out kits really necessary on a road car? If I go for option 2 above, can adjusting the length of the upper arms help counteract the geometry issues? If I lock out the camber adjustment, are the upper arms alone enough to adjust the camber or do I also need the GT3-style lower control arms? How do you set the length of the upper control arms if the eccentric camber adjustment is still in place? Does anyone other than the usual American suspects make cheaper lock-out kits? Do the Porsche GT / motorsport cars have eccentric adjusters? If not, do they have different subframes or is there a factory 'lock-out' kit? Is the best way to fix this issue to raise the subframe? If so, can this be done with factory parts? I appreciate this is a lot of questions. It's got pretty well out of hand in my mind already. I should probably just throw some of those cheap Gravity Performance toe arms at it and forget about it, but I'd rather not pass up the opportunity to get this solved properly, if I can. Any and all opinions and experiences welcomed! Thanks much.

Even wear doesn't necessarily mean the set up is correct, since my GEO was done by Charlie of William Francis the car drives great but it now uses front tyres as quick as rears.

My money is on the road surface where it happened. How many bends have you been round where the car didn't do this? Then on one occasion it let go like it did. You only need a bit of diesel spilt on the tarmac on a bend and it's game over. Also could be a bad unnoticeable camber. There's a roundabout near our NW meet and over the last 4 years or so of meeting, around 20% of the time there's a ditched or overturned car in the same place. The dampers make it remarkably capable and confidence-inspiring, I can get it to turn in where I want, it's fast, and it's comfortable. Nonetheless it caught me out, somewhere I didn't expect it to let go.

Get on a big open empty car park and see if you can replicate it letting go.

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Okay, thanks. What parts have you used to get to those figures? Yes, absolutely, the surface was a factor. My next door neighbour, who is a biker, immediately suggested diesel as well. It was damp, it was late, I had been driving all day, we were close to home. All the common factors. I got complacent, I wasn't paying enough attention, it was a useful wake-up call. This was far too fast to replicate in a car park! It's nice and easy to catch at car park speeds. I'm sure that nothing is fundamentally broken, and the major factors in what happened were definitely me and the environment. I still trust the car not to bite. But either way I'm not happy with how the tyres are wearing and I'd like to check that I'm giving it the best chance. Here is a new Michelin for comparison, you can see how the tread blocks on the shoulder have worn to nothing. Still keen to hear what parts people have actually fitted to lowered cars, and how their tyres wear. Thanks

I may have just answered my own question, by cross-referencing the parts diagrams for Carrera and GT3. Of the: lower control arm, upper control arm, toe control arm, subframe and eccentric adjusters; all show the same part number apart from the toe adjustment bolt and washer. I have also read that the subframe sits 7mm higher on the GT3 than the Carrera. My guess therefore is that this is the right solution for a road car. I will probably take a punt on the GT3 eccentric bolts, and then raise the subframe when I next have cause to drop the engine / rear suspension. Unless anyone has experience using these adjusters and can confirm/deny that they work on a Carrera? Thanks

References for future readers: Elephant Racing • Subframe Bushings & Spacers For Porsche 996, 997 www.elephantracing.com N Thread 'Solid rear subframe bushes' 12 Nov 2019 I'm planning on stripping the rear subframe as part of my overhaul. On a google last night I see design 911 do some solid bushes which change the height. What they're saying is that on a lowered car it will help bring the geometry back into spec. Has anyone gone this way? Will this do away with the need for adjustable toe arms? Also these are £200 for a very simple looking bush and washer. Has anyone had these made? As usual, all help and pointers welcome NedHan79 Replies: 30 Forum: Porsche 911 996 (1997-2005) The symptoms described on the Elephant Racing page fit.

I wasn't suggesting car park speeds. Hence finding a big empty one.

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It's in my sig, H&R lowering springs, Koni Special active shocks, all new arms and GEO by Charlie.

My personal opinion is that you should also look at your tyres. How old are they - might they have hardened a bit? Also Michelin PS5 will give far better grip in all conditions (but particularly wet/damp) than a PS2. And for a proper UUHP choice - ideally get some Conti SC7 on there, which will blow the doors off the PS2, again, especially in wet conditions. Are you able to describe the factors that contributed to the spin? Lift off oversteer / power oversteer etc? Hope the rest of the damage wasn’t too bad! One other way to get a handle on the handling, so to speak (especially if you need speeds in excess of what you can achieve in a big empty car park) - would be to book yourself on a track day. Shred up what’s left of these tyres then put some more modern ones on

I had a similar experience to you where I lost the back end of my car in circumstances that I really shouldn't have, I was so shocked I just ended up driving off and didn't really think about it until the next morning, but I wish I'd have gone and had a look because I bet I'd have found diesel or some sort of contributory factor. This does sound like one of those moments. However, with regard to the mechanics of your vehicle, in these sorts of situations in the past I'd get neck deep in the details and try to fix it all myself, especially because I like learning, but as I've gotten older I've realised the amount of skill involved in getting things perfect. For example, I doubt there is anyone at Centre Gravity that could just walk in and do my job, even with a few weeks of intensive training, so I'm not going to assume that I could get anywhere close to doing theirs with all their years of experience. So basically what I'm saying is fair play for taking it on, but these days if it's something that I think needs years of experience to really know what you're doing then I take it to the experts and part with some cash to get the job done.

Whew, so many questions! I'd be looking at the simple things before trying to change out suspension parts; as suggested above, old tyres, mismatched pressures, some ice/oil/coolant/diesel on the road, even a different line or a different braking point can destabilise a car... Back when I was younger, I've spun a 7 series on a familiar corner once (!) and still never found out why, even at the same pace. As to your current set up, you seem to me to have a lot of rear camber, and a fairly low -30mm ride height. I'd be tempted to raise it maybe 10mm and dial out some of the camber, to allow the car to roll onto the full contact patch in a corner. As to toe, I don't think that's excessive, as my rear settings are close to Thunderrace above, and my rear feels very planted, but a lot of miles will wear the inside shoulder. But as Harryblue suggests, you might be best off starting your investment at CentreGravity.

I dont think your geo is to blame, mine is similar (a tad more camber all round), i needed adjustable tie arms for the rear the get the toe and the camber to the 'right' values, the car is ridiculously planted! I suspect Alex is probably correct in that there may've been something on the road? A full spin is a pretty drastic thing and i think you'd find issue on every bend if something was that far wrong.

I agree, your camber is too high and will wear your tyres out in no time but it won't be a huge factor in your spin - in fact it should help. What I would add is that a 911 'letting go' is not like a front-engine/rwd car 'letting go'. Completely different technique and nowhere near as predictable, once it starts to go and you're at high speed and not expecting it, it's almost impossible to recover. I wouldn't beat yourself up.

I concur, it happened to me a couple of times on ‘greasy’ Winter roads. Pretty sure one was a diesel patch as it felt like I was on ice. I decided to slow down when the grip (and my talent) wasn’t there. Problem solved, it hasn’t happened again! Practically though, I’ve changed tyres and they have more grip in cold conditions. Adjustable tie rods were needed to get my rear in spec without excessive camber (x74 geo) and I don’t have uneven tyre wear. My C2 is lowered with M030 dampers & Eibach springs (initially low, so currently using with 17mm perch spacers for ride height/pre-load). Dampers aren’t particularly compliant on bumpy back roads (better with more weight in the car) which is another reason to take it easy when slippy. Never had a problem with rear grip in the dry although I don’t use the roads as a track day even when pressing on.