At the track test for these new Michelin PSS tires, one of our first conclusions was that the car was aligned with too little camber for enthusiastic driving, let alone serious track work.

Anybody know what range of camber and toe-in are provided in the stock suspension set-up for a 997.2S with PASM? And is a corner-balancing step possible?

Gary

 

as i understand standard 997.2 street shocks do not have rings so you cannot corner balance the car. stock max camber in front is limited by -1 deg, toe is usually set close to 0 there.

if you will keep rear toe set to 0.10 then stock bits will limit camber to -1.8 somewhat.

usualy solution is to 'upgrade' street suspension with gt3 car parts - LCAs, upper mouints, put in adjustable toe arms in rear, adjustable fork arms in front (for castor).
you can ask on gt3 forum if stock gt3 shocks can be adjusted for ride height, imho they can but i am not sure.

 

Thank you, Paul.

My current plan is to stick with the stock S components, which are satisfactory in track work even though they're not aligned yet to get all the grip these tires could manage. I do want to make the camber more negative and the caster more positive while keeping the Porsche-recommended toe-in settings. Initially, I was tempted to fiddle with the toe settings to reduce the understeer, but I found that a more aggressive driving style dealt with that issue. The car was drifting nicely through corners ranging from 50 to 100 mph at the last track day. (So there's no point in risking the high-speed stability when I can just ramp up my demands in the other corners)

What I have in mind might be called a 'performance' set-up, meaning one that suits an aggressive driver on street or track, rather than a full track setting. Maybe I'm getting old and wimpy, but a full commitment to track performance just sounds ... tiring at my age.

I should be able to get this data from the guy doing the alignment, but I'd really like to go in knowing what a knowledgeable mechanic should know. Otherwise I'm at the mercy of him reading the wrong line from his manual and giving me the set-up for the non-PASM suspensions or the sport suspension. And that's giving him the benefit of the doubt. In some shops, I might end up with the set-up for a '57' Chevy.

So far, we're talking about:

Front: Camber -1° left and right; Caster, max positive; Toe, per Porsche recommended setting.
Rear: Camber -1.8° left and right; Caster, max positive; Toe, again per Porsche recommendation.

Anybody know the range of caster settings?

That includes no cross-camber or cross-caster, which compensate for the thousands of miles we drive on crowned roads that slope away from the center line. That is, a 'cross' setting minimizes drift toward the side of the road and is rarely used on road racing set-ups. (Works a treat on ovals though, or so I'm told.) I'm considering giving up a quarter degree of right-side camber front and rear and maybe a quarter degree of caster on the left-side as well, but I'm not sure it's necessary. Anyone have experience with putting zero 'cross' on a car driven mostly on the road? Is it annoying? Or not even unnoticeable for an attentive driver?

Gary

 

+1 what utkinpol said.

997.2S cannot be corner balanced for sure since the struts are not height adjustable.

GT3 struts are adjustable but I am not sure I would advise just swapping struts as there are a bunch of other differences between the two cars and the 997.2S PASM modules may start acting funny. They only PASM compatible solution I know of are the damptronics.

Some people have reported getting to about -1.5 to -1.8 max up front on PASM, SPASM is a little less at about -1 to -1.1 because the car is lower.

The suspension on these cars is very nice and the multi-link system allows for orthogonal adjustments. The downside is that once you start changing parts to "expand" the settings range, you pretty much have to change everything because it all works together as a system.

If you do not lower the car, just swapping the stock LCA's for GT3 adjustable LCA's will get you to about -2.4 or 2.5 deg of camper up front. Many suggest that front camber should be kept at about .5 from the rear. So without changing anything in the rear, you would be able to try something like -2.3F/-1.8R keeping in mind that you want the toe and caster in decent shape. If you lower the car, the the range of camber adjustments becomes narrower again because the rear toe will be screwed up and the cycle start again with rear toe links... As you can see, this is a slippery slope...

Even though it is not enough for "serious" track work, you can get a lot of mileage at the track the -2.3F/-1.8R that LCA's will get you with a minimal cash outlay (~1K installed w/alignment), and it is liveable on the street; with toe close to zero, it will keep tire wear in check but keep in minds that it also will make the car tramline a little bit. The next step up is top $$$ if you want to do it right like utkinpol did with his JRZ's and at that point, the ride becomes very stiff for the street.

Hope this helps,

T.

 

Gary,

Sorry for my double post, but you posted before I finished my writeup...

Like you mention in your post, these cars are set from the factory to have a considerable amount of understeer, most probably as a safety measure because so many people wrecked early 911's because of their snap oversteer personality. The first thing you probably want to address for the track is to bring it back to a more neutral behavior...

Considering that, if you do not change anything else, I would advise against having a lot more camber in the rear than in the front. With that in mind, I think the front will be the limiting factor so you should ask your mechanic to max out the front and keep the toe at 0 and caster at 8'. If he can get let's say -1.5 on a PASM car, just subtract .5, giving about -1' and make that the rear camber setting with the toe at 0.12.

There is a slight variation of what some people have reported as the max in front depending on their mechanics knowledge of the car, I even heard people getting to -1.8 deg with PASM. For example, the front towers have a little play on their mount so you can adjust them just right to maximize the camber (just be careful with caster if you play with the upper mount)... But that is more an art than a science at some point.

I find it very annoying when on the highway. But I can't afford aligning the car every few weeks so I live with it...

Hope this helps,

T.

 

It does, T. I agree about that slippery slope. More important, I made this promise... Well, it's like this. I lost my medical for racing over 15 years ago. '94, what's that? Okay, 17 years ago. Time flies. And when I ever so casually mentioned wanting to spend a day at Willow "just to confirm the handling of this new car" I got a... a look. Despite her stroke, we've been married 49 years and Cindy isn't slow to read me. I had to promise no nine-tenths stuff, nothing that requires my Nomex to come out of storage, and a few other concessions. ("No helmet stuff" at first, but I convinced her the old fuddy-duddies wouldn't let me cruise the parking lot without a helmet.)

If I'm not going to tune the suspension for my fastest lap, the odd bits from a GT3 or the aftermarket won't really matter. Sigh. All I really wan... well, all I really want is to be a squeaker again. Even fifty... ish... would be fine. But I'm not, so I'm going to settle for making the car fun to run once in a while. Nothing serious. Just the odd best-in-class maybe. But I won't brag about it too much if that occasion should arise. Not at home anyway. Maybe here.

So I'm honor bound not to make a race car -- or even a serious track car -- out of this C2S, lest I end up in what I deserve: a CL63 or some other old man's car. (Or an electric wheel chair if I don't follow her good advice. Damn the good advice. Especially when it's right.) All I'm really out for is a brisk drive to keep my mind active and my skills safe, right? Maybe adjust the alignment settings a tad here and there for the sake of better tire wear, right? Just a day in the sun, no red mist, right? Right.

But it does keep me off the street and out of trouble.

Gary

 

Gary, I've been tracking the MPSS for the past 8 track days and you're right that as good as the tire is, the stock camber just doesn't cut it for the track. Is frustrating that the carrera line doesn't allow for more adjustment in this regard.

The dealer maxed out my front camber early in the season but it's still not enough for me (though my car is heavier than yours and has more understeer tendency due to the AWD). Ultimately, now that my speed is up, I've corded the front and rear left side (tracks here are righthander biased). So my car is at the tuner where he'll let me know this week whether he can squeeze more camber from the fronts, otherwise I'll be buying LCA's. Given your vast track experience, I have a feeling you're outdriving whatever camber you could get out of the stock setup.

Have you also considered sway bars? Seems like a relatively cheap mod with little compromise on the street that will help towards the similar goal. Also adjusting those bars is a traditional solution to understeer/oversteer, plus they are adjustable (for when the track season is over). I'm putting on some H&R's this week.

The LCA's also seem not too compromise much of anything on the street, so I'd also put them in the "doesn't hurt anything but your wallet" camp of mods. Unless you get too aggressive with the camber and/or toe and get uneven street wear. But the MPSS have excellent wear characteristics so that should help.

I think the tougher decision for you would be whether to go for the coilovers (unless you have Sport PASM). That seems to be where one makes real tradeoffs on street driving versus track (though some report no street issues at all). Also seems with these you run the risk of clunking or other noises. For me, also have the added issue of not knowing how the heavier roof dynamics will play out. So I'm probably waiting until next season before deciding on that one.

 

Wow. Hopefully not the new MPSS tires... That's getting up into Jeremy Clarkson territory when you go through a set of tires in eight track days. I assume the outside is where the problem is occurring? Did the dealer also max out the positive caster, do you know? That creates an effective increase in camber when cornering. (Or so I've been told. I never worked out the mathematics of wheel dynamics myself.)

Just barely half vast, what with working the hours that probably epitomize most of our careers. But the time does add up over the... what is it, a decade or so since 1965? Something like that... mutter, mutter.

My solution to the car's alignment had been to keep it light and cheery and make jokes about John Deere (It runs, but it plows!) until we took along the pyrometer and a good quality gauge to figure out what was happening. Then I was able to see which end needed some help getting heat into the tires and modify my driving in that direction. This last track day, it certainly wasn't optimum in terms of absolute grip levels but a current Carrera is so damn fast compared to most cars, even other Porsches, that I had a lot of fun catching people in the twisty bits and passing them on the straights. I'd say the car isn't more than eighty percent of what it could be, but if I drive it respecting the limitations of the road suspension settings, it is ... brisk? Yes. Brisk is a good word.

I did consider sway bars first when I realized how much a Carrera driven mildly wants to plo... uh, understeer 'safely'. That first track day I wanted to pull the one off the front completely and double the one in back, but that was just a frustrated reaction. I was... annoyed. This was my first Porsche after wanting one for forty years. I hadn't been thrilled to be forced to change cars by the dealer crashing Cindy's NSX, but at least I had my dream car now. And it turned out to be a pig that couldn't turn round in a traffic circle.

Or so it seemed. That first 'instructor' riding with me could only suggest that 911's love power in the corners. "You need to transfer that weight to the rear where all the grip is." Fair enough, in his 1976 Targa S (which I'd love to drive some day), but it sure wasn't working for my Porsche. The more power I used, the more it pushed the front tires sideways across the track. "How do I get this pig to rotate!?" sums it up.

The second track day was a little better, but only slightly. That's why I changed tires and took along the instruments to see what was going on. Now, I'm driving it in a way that puts the load on the rears early in each corner and I'm balancing it there with throttle. I am easily twenty percent further past the apex than I'd like before I can turn the throttle back into a go-pedal instead of using it to pick the direction, but it does get us around pretty quick judging from how fast we ate up the Boxsters and 914's in the corners at the Streets. Those are cars that handle well, so with that change in driving style, the car wasn't a slug at least.

They did a lot right with the 997, but clearly they didn't mean to encourage people to drive it at track speeds unless they had the track experience first. A bit of a Catch 22, but I'm sure they'd say that's what their driving school is for. Very likely, they teach pretty much what I'm doing, give or take a degree of camber in their school set-ups. At least to the advanced students, maybe not the novices who go there cold.

And the car is great fun, even now. I'm just hoping to sharpen the response a little bit by taking the 'preferred' Porsche settings to the maximum they 'recommend' in the direction of performance driving. Modifying the car visibly would upset Cindy a lot. She is justifiably nervous about this foray into youthful derring-do. Modifying it discreetly (like sway bars) wouldn't be much better, because the truth is I'd just go faster yet and I probably shouldn't be going as fast as I am now. My neurologist would prefer I just buy a damn Lamborghini and a ZR1 and a Ferrari and sit at home driving them on a Playstation 3. So I'm happy I'm getting away with using a real track.

Besides, I've got to admit that going through the kink and over the Waterfall at the Streets at 100 plus is a charming ornament to my retirement. Just enough to remind me what it was like in formula cars, but not enough to get me confined to the loony ward. If I started going over at 110 and catching air, they'd be waiting in the pits with a nicely tailored jacket I'm afraid.

Gary

 

That's very helpful, T. Excellent detail. You think it's best to keep the camber less negative in the rear? After reading that document you sent me, I was thinking I might go half degree more negative than whatever they can reach in front, just based on the greater tire width and the car's intense desire to plow. But I'm looking for the voice of experience with this problem. That's why I asked. Sounds like half a degree less negative is the better choice? And maybe some small concession to 'cross' since the bulk of my driving is on roads?

Thank you,

Gary

 

Gary, seems like you're thinking of camber primarily to gain a bit of performance whereas my immediate concern is for the health of your (and my) tires.

When I got my T4S, I considered the exhaust mods necessary, because I was unhappy with the stock sound (and sure, a little extra power is always nice too). Regarding the stock suspension, I did and still do think it handles well enough --- a thrill actually, on and off track. With the stock setup, I was tracking as fast as I wanted to and generally not looking to be Walter Rohl. I would have been more happy to never do any suspension mods and not have to deal with the time, cost and risk of unintended consequences (on the street). Axles

The only reason I'm modding my suspension is because it just cost me a pair of tires (corded the left outside edges on both tires) and I'd be a fool to continue ruining MPSS without addressing the cause. From the great advice I've gathered on this forum, it seems that at some point, when one's speed hits a certain level, one may outdrive the car's stock capabilities and cord tires. That's what's happened to me -- I drive pretty close to the traction limit, maybe a bit over (bit of squealing) here or there but I'm not drifting like some Englishman fronting for BBC groupies . I do believe in driving for the clock, not "styling." The death knell for my current MPSS was an open track day at Monticello last week. Went through 2.5 tanks of gas over the course of the day, so more like 2.5 track days! I let the tires and brakes cool here and there of course but it didn't matter (and probably irrelevant to the cording). For some, maxing out the stock front camber is enough. That was not my experience. I didn't address caster bc I thought those were un-adjustable on these cars.

Not sure how many track days you're planning on doing. Maybe just keep an eye on your tires, rotate them along the way, and see how the wear goes. No doubt driving style plays a role.

 

Gary,

I finally realized that, on these cars, pretty much every possible suspension variable is erring on the side of understeer. I think it is possible to drive around this condition but, depending on conditions it may not always be possible. IMHO, a car should be as neutral as possible if you want to consistently have fun at the track...

Big tires in the rear, small tires up front. Soft bar in the rear, stiff bar in the front. More camber in the rear than in the front. Wider track in the rear than in the front. And on, and on, and on... Essentially, it took Porsche 50 years to figure out how to make the best of the inherent pendulum effect of an engine with it's CoG behind the rear axle, and make it possible for wannabe's like me to drive them on the track without killing himself because his *** is faster than his head... In fact, if you look at some of my posts from last year, I was essentially describing the same initial feeling you had with the 997.2. I was coming from a well dialed in standard 996 C2 and I just felt that my old car was very sharp compared to my new 997.2. What I had not realized is that since there is so much more power on tap with this fantastic DFI 3.8L engine, that Porsche probably thought it best to add even more understeer...

But I digress...

Back to your alignment question, the values I PM'ed you are the factory settings from the shop manual. The manual doesn't indicate what the max/min reachable by the components are.

You should just max out the front to whatever you can get since it is the limiting factor, try moving the towers a little to squeeze as much as possible but do not go over 8.5 deg of caster or you will get fender rubbing when turning hard under front compression. I had 8.9 at some point and it cost me a liner to learn my lesson... This should get you to about -1 degree in the fronts.

From what I have read on this board, I would also recommend keeping the rear camber within 0.5 degrees of the fronts, I prefer less camber (e.g. -0.5 deg) in the rear than in the front but that is just me. Some people have more in the rear (e.g. -1.5 deg) and seem to like it too but I am pretty sure that I see more people with more camber in the front (which makes sense given the default behavior of the car).

This more/less, positive/negative gets old pretty quickly, hopefully, you get what I mean because I am not sure I make sense at this point. Maybe I should get another scotch?

But I digress, again...

For toe, I would suggest to start with toe-in 2 mins per side on the front and toe-in 12 mins per side on the rear. That is what I had before and liked it better than what I have now. I currently have zero toe in the front and and 2' in previously. I will be going back to that setting... Toe makes the car easier to drive but the downside is constant tire friction that translates in tire wear. I suspect that this zero toe is what I feel on the highway that I do not like (a constant feeling that I am sliding to the side the highway is canting to). You can see if you want to add cross from there but I am always worried about doing things that will help the car to one side only - this is not NASCAR after all...

The problem with all this stuff is that is is all interdependent; the mods you make, the tracks you run on, the tires, the driver, etc. There are a LOT of variables and I have a feeling that I am going to go broke before getting to my nirvana settings...

HTH,

T.

P.S.: I am asking Santa to bring me a set of SmartStrings for Xmas...

 

and...

Mild oversteer would be my usual preference. (Ahem. If you consider a seventies 911S to have 'mild' oversteer. My usual track car was a Formula Ford which makes an early 911 look like a Mini-Cooper. So yes, I would be inclined to set up a car for oversteer. ) Notwithstanding all that...
I wasn't a Porsche owner in the 996 era, but I think your reading is almost certainly correct, T. They designed with the specific goal of making sure the handling would be benign in routine 'sporty' driving and they succeeded. I would assert they managed a nice hat trick though. Ours handles comfortably in boulevard use, benignly in the back roads, and yet handles like a race car on tracks. We'll talk.
And so do I. We were talking about suspension settings.

Now this is an interesting thing. I'll have to think about this for a couple of days and maybe pull out my copy of Race Car Engineering by Falkenburgh. I always thought of camber as... well the way of keeping the tread flat in different cornering loads. With really good suspension (that is, us versus the swing axles of a sixties Spitfire), the wheels are pretty much perpendicular to the road but the tires in a fast corner are producing shear loads on the sidewalls. Those tend to lift the tread on the side toward the direction of travel. In a fully dynamic computer-controlled suspension, even this effect would be balanced out by the computer, but so far we don't have such things. (And I'm rather happy about that actually.) And we still have to turn both directions, unlike oval-track racers, so we favor the outside tire of course, where most of the load transfers. To keep its tread as flat as we can get it, we pre-load the tire by tipping it inward when viewed statically. When the high sideloads arrive, the tread will pull the tire toward the direction of travel, which is inward for the outside tire, and that will flatten out the tread.

We don't do this to "put as much rubber on the road as possible" as I read in one fairly naive book. The size of the contact patch is determined by the tire pressure and the load. But if the tread lifts on one side, the other side of the tire necessarily compresses because the contact patch must stay the same size. When that happens, our tire that could have been pictured as a rolling pin just became a rolling coin. And that causes some pretty funky handling. (We could have sold popcorn when a sixties Spitfire would try to run wide tires. More fun than watching a bear dance.)

So I'll have to think about this, as I say, but I don't think of camber as a way to get more performance, just more predictable handling and more even tire wear.
Always the impulse when suspension settings are being discussed. I've noticed the effect over many years.

Heh. I had to Google that name. You are wayyyy farther into this then I ever want to be, T. Now when I was racing, maybe. But these days... well, I'm more likely to be checking the loft and lie of my irons than measuring my suspension settings for myself. Don't we have minions for that sort of thing?

Toe settings are something else I need to consider longer. I always thought of toe as a way to control the compression of the suspension bushings under load. You know, assuming RWD, the front tires pull back on the front suspension and they need static toe-in in order to be rolling straight ahead in that mode. Meanwhile the rear tires are pushing forward against the net drag on the car body, including that front-tire drag transferred through the body, so they have to start with a little toe-out, or neutral at worst so they'll be rolling straight ahead when the torque compresses all those bushings under load.

That's a pretty simplistic view. It is one basic function, but not the entire effect of toe settings, and with a race car I never worried about it honestly. (Solid bushings you see.) I need to think about toe settings on a road car, even one being used on track. I was just going to follow Porsche's toe specification, but your suggestions sound like they take into account handling effects I never considered before. Falkenburgh, definitely Falkenburgh, and then I may have some questions, T.

As for your comments in aggregate, I agree completely. We had notebooks, and different settings for each type of track.

Now as for caster... Sigh. I'm already Scotch, but maybe I can find a nice Irish Mist in the cupboard...

Gary

 

Gary, i did not read entire thread - I would advice to do this:
install RSS LCAs in front
http://forums.rennlist.com/rennforum...available.html

then install rear toe arms
http://www.tarett.com/items/996-997-...lnk-detail.htm

that alone will allow to set camber to more or less proper -2.5 deg front -2 deg rear. you may not need anything else.

i do not think you will like how 997 car behaves having whole 1 degree of camber more in rear than in front as you got it now. you got so much understeer now that it is really no fun.

then after that you can install GT2 or GT3 set of sway bars if you want to limit amount of body roll - you will see if even at -2.5 front camber you still will be burning outer edge of your tires - that means you need stiffer sways.

to be able to ajust castor (or caster - not sure what is right spelling) - you need to install adjustable fork arms.
http://www.tarett.com/items/996-997-...010-detail.htm

as of dogbones - it is also optional, i do not think it makes much sense to do unless you are prepping car to run on slicks. look up tarett catalog there, it has all that one may need and they use great quality ERP monoball rod ends.

PS.

also, for track you need to put on cooling ducts, if car does not have them now.
those are best
http://www.suncoastparts.com/product...7brakeupgrades
or these
http://www.suncoastparts.com/product...7brakeupgrades

 

Thanks for the discussion... Thinking about this aloud is really a good way to crystallize my (very basic) understanding on this.

Completely agree. I would like to add a twist though: there not only left/right weight transfer but also front/rear and that is where the complexity is (at least for me). I come from a motorcycle background where things are very simple: there is no driver aids, only two wheels - and unless you are turning, pretty much only one wheel on the ground. The weight is in the middle _and_ you can just move the weight around (weight forward at turn in, weight back at exit), etc. This whole "having four wheels with a weight distribution you can't change" really makes thing more complicated to understand.

To go back to your "rolling coin" analogy, I really have to think about two "rolling coins" or "teardrops" on the exterior side of the car (again not taking into account the interior too much, although I am sure there is some implications there - but we always do that with physics: don't sweat the small stuff) where the front and rear coins need to be in balance with the weight distribution of the car if we want it to do what we want *predictably*.

When you are turning a car, by definition you are trying to make the dront of the car want to make a smaller radius than the rear of the car using front tire friction, which then forces the rear to get in line because it too gets angular traction once the front has turned it, so, assuming a weight neutral car going at constant speed on a flat surface that has the same friction everywhere, doesn't that means that the front will have to do a bit more work since they are going for the short radius? Now, front friction is the usual way to turn a car, the second way is to help it a little with some oversteer and "throttle steer" the car around the front to "push the nose in"...

Getting back to our camber settings discussion on a 911, because more static weight is in the back, more rubber is in the back, softer swaybars are in the back, and more radius is in the back, the fisrt thing we need to do is to load up the weight on that exterior front tire to "cheat" our way to a turn. We do that through straight line braking before turn-in, and trail braking into the apex, but on a 911, I find that this is not enough and I need to give the front some more help in the way of additional camber in the front. Actually, I run wider tires than spec in the front, spacers in the front, more camber in the front, and stiffer sways in the rear - so OK, that is a LOT of help... BUt I now have the feeling that I can move the weight front/back with both pedals. I can also move it very effectively with the left pedal when I screw up, but that is another discussion...

MMmhhh, this paragraph just made me realize that I am really seeing an ideal car just like a bike... With only one wheel on the ground at any given time... Now I really need that new diff.

Sorry, I wasn't there in the 60's. I bet you I would have liked the 70's though... But I wasn't old enough at that time to enjoy those either...

Same here, that is how I got into this mess at first... I was just trying to understand how I could have wasted a brand new set of SportContacts on my 996 in about 2 hours of track time... Slippery slope...

3/4" long. 2' flat and 1' weak on my MP-14's here. That's too simple and not dangerous enough. I am convinced that I can play 120 with any clubs anyways, it's all about style

Toe is a b*tch for me to grasp too because it is a full on 3D model that is completely dynamic. You start with static toe but then, as the car moves forward, left/right, and up/down, it keeps changing. Then you have the relative effects of camber, caster and bumps... So I just took other people's advice with 2min-in/12min-in F/R and used that. It seemt to work. Then I tought I would venture on my own with zero in the front and I don't like it... Sometimes learning from other people's mistakes is the way to go...

I am putting "building a full on 911 suspension simulation model and doing some finite element analysis on it" on my list of things to do before meeting the grim reaper... Right now, I gotta work to pay for the lab part of the experiment.

T.

P.S.: If someone has 3D CAD files of a 996/997 or even 986/987 suspension please send them over...