RonCT

Well, I'm starting to understand a rear engined car. I'm thinking that my 997S has a bit too much understeer and I was theorizing yesterday with a few RennListers at LRP.

First off I suppose I could adjust the alignment... Right now I'm set up for street with very little camber up front and only about 1.3 rear. I understand I could max out at about 0.80 front and 2.5 rear...

What about different sway bars and how would that help?

Another thought is pressures - I understand if I increase rear pressure it could reduce understeer slightly. I was running 40 front 42 rear on PS2s.

I will be consulting with experts that I will ask to do the work - but your comments would be appreciated so I understand what to ask for better (and will appear informed when I speak with the gurus).

Thanks,
Ron

nkhalidi

Same principles as the M3 game, Ron. For less understeer: more camber in front, less camber in rear, higher pressure in rear, less pressure in front. Anything to increase grip in front and reduce grip in the rear will result in more neutral handling. Of course, you can go too far in one direction and create an oversteering monster a la 930s, et al.

Just as a data point, my car is at -1.5 in front, -2.5 in rear on PSCs and it still understeers, as evidenced by the front tire wear. Or I could just be entering turns too hot and scrubbing off speed with the tires. Not exactly sure. For my next alignment, I'm going to try to eke out some more front camber and leave the rear at -2.5.

Also check the 997 GT3/2 board; those guys have the same basic architecture as we do, and there are far more track-oriented people there than here.

Alan Smithee

Don't think so...

RonCT

Just quoting what Michelin says in one of their guides about their tires at the rear of a 911: "...increasing the pressure will tend to reduce the understeer slightly.

Maybe it's so slight nobody notices?

elh0102

There is no inexpensive way to get much camber up front. Mine is maxed out at less than -1.0. In comparison, in an E46 M3 I set it around -3.5 for track, -2.0 for street. You will probaby need to either replace the lower control arms with GT3 parts (if they will fit) or, go to camber plates, which will probably require a suspension change. After spending a lot of time and money on the M3 suspension, I have decided the 997S stays stock. Sure, it can be improved, but for my casual track use, (6 or 7 events a year), it's just not worth it (to me). And frankly, the car can be driven very fast as is, if driven well. But it's a personal decision.

You could look into a larger rear bar or softer front. You might also try running without the front bar to get an idea of the effect. You could also try equal front and rear tire pressures. Generally, you do want more pressure for more traction. But I would urge caution. The last thing you want is to get into oversteer. These new 911 cars have impressive rear traction, which allows us to use a lot of power through the turn. Indeed, that carries with it some on-throttle understeer, but that's relatively easy to manage, and doesn't slow you much, if any. Good luck, and post your results.

stom_m3

Tire pressure is a maximum curve with different driving styles associated with lower or higher tire pressures. On the lower end of tire pressure the slope is greater and the window of grip is narrower. With higher pressures the slope for grip is wider thereby generally being safer and easier to be herky jerky on the wheel. I've never thought the 997 had that much understeer and I have to wonder if it's more of your driving style than actual chassis setup. That said, I have no idea of your track experience or driving ability.

MHC2S

Please let us know what you find and if there is any kind of adjustable camber plates for our stock suspensions, though I doubt they exist.

kauai_diver

I would also ask/find out what your toe-in settings are and if changing those values would help.

ezinternet

If you really want to try to dial out some of the understeer (that Porsche engineered in :-) what are the range of options to increase the width of the front tires, specifically:

- what's an effective next step up that will still fit comfortably on the stock 8" rims - how wide, and what tires?

- if one swapped into 8.5" fronts and then what width could you get?

- is anyone running a 9" front on a 997 C2S/C4S?

Aren't these one of the steps, along with different springs and anti-sway bars, that are used on the 964?

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-ez

GSIRM3

I know Porsche has done a good job over the years reducing the oversteer of the 911. Have they dialed it out to the point that the car now actually understeers? I have a M3, and it does understeer, as required by BMW's lawyers, but I figured the 911 would still have more oversteer tendencies than understeer. I have owned several 911s, but not in the past 15 years. All of mine tended to oversteer, at least at the limits.

Dave07997S

Exactly, I was thinking a 8.5-9" width rim with a 245/35/19 or a 255/30/19 on a 9" wide rim. That ought to solve that understeer quite nicely. I was probably going to put 245's on the OEM lobsters even though they are only 8" wide.

Dave

Chris R.

I don't know how you drive Ron but if this is your first 911 then maybe you have to adjust to the way you are going into corners. A 911 needs weight on the front to turn; trail braking is something that you may want to try to see if it helps. Maybe I'm wasting my time and you're a very competent driver...
Alot of people (new to 911's) tend to turn in on power and the car starts to understeer so they crank in more steering and it just gets worse.
Again, I hope I am not offending anyone as I don't know how you drive.

On my Cayman S, I am running -1.5 in front and -2.0 in the rear and it's not too bad. I'm running RA1's. On my stock alignment I was getting a ton of outer tire wear (front AND rear) so I really needed to get some more camber. I have not tracked the car much since the new alignment (and springs) so i have not found out of it's fixed or not. Tomorrow should give me a better idea.

If you can't get enough camber stock, you can slot your top plates (well, the chassis) to get a bit more out of it or you can lower the car, effectively giving you more negative camber. I don't think there are camber plates that will work with the big factory springs...but maybe.
Good luck!
Chris

Alan Smithee

Porsche has virtually eliminated historical lift-throttle oversteer, but 911s have always had steady-state and power-on understeer (big HP and Turbo cars excepted).

malammik

Adjusting tire pressure is NOT the right way to tune the suspension. There is an IDEAL pressure at which you will have most grip that's what you always want. Compromising grip to avoid understeer or oversteer is just shifting the problem from one place to another. Increase camber or better yet have fun and learn to drive the best with what you've got.

Find an expert and let him drive your car. Then continue to improve your driving skills until you have the same lap time as he/she did.

Higher pressure does not always mean more grip too btw especially if your tires already look like donuts.

malammik

+1. porker needs more weight in the front when turning. braking sure does add it.