unstable at higher speeds

[911dark]

Hello all!

I recently purchased a used '99 C2 with a 6spd. My previous car had been stolen and I had always wanted a 911 so...

My previous couple cars had all been Subaru Impezas (Subie and bike) with the last one being quite well modded. (310awhp) I had done a couple track days with it and it was an absolute blast! She was found 48hrs after being flat-bedded from my driveway. :( Recovered Subie

Anyway on to the question, my 996 has 65K miles and seems stock other than the hack job someone did to the sound system. (what they did in the door panels and to the stock harness connectors should be criminal!) At speed (70mph+) and under hard acceleration the car feels unstable. Turn-in feels good and quick but then for lack of a better way to describe it, it feels like "bow steer". Excessive roll in the body that tightens the turn suddenly. Under hard acceleration there seems to be a large abount of weight shift.

I know there is one serious issue I need to resolve, the tires are currently mismatched and will be replaced once I settle on what new wheels to get. Currently it has Front: Continental 225 40 R18 and Rear: Capital 265 35 R 18.

Alignment may also be an issue as it seems to wander a bit on the highway at speed. Or perhaps it was setup for track. :clapping:

I do have Fabspeed headers, cats & mufflers on order and will have the Motronic tuned on the dyno. I'll post before and after torque curves once they are installed.

So am I just use to the AWD and very rigid chassis of the Subaru or is my 996 in need of some serious upgrades?

[viper501]

Tires and alignment should go a long way toward fixing handling issues. You might also want to determine which suspension you have and whether you have any factory or aftermarket ground effects. If you have the factory aerokit 1 (aka taco tail ) make sure that it hasn't been fiddled with and make sure that they have the correct bumper. Pictures might help somewhat in identifying what parts and pieces you have.

[Richard Hamilton]

I totally agree - first step is a good 4-wheel alignment check. If it is off, the correct setup will transform the car. I'd reckon it is worth having this done once every couple of years. Small changes, particularly to toe and camber, can make big differences to how the car feels.

[Danyol]

Congratulations on your purchase!

I had a very similar experience to this with miss-matched front & rears. The 911 is a very "transparent" vehicle which will telegraph issues with tires and alignment.

Recommend get a matching set of tires & have the car aligned, there are a number of great tires out there for the 911, do a search on the board. Are the Continentals Contact 2's, Porsche have a list of recommended tires with an "N" designation. Our gracious host Loren has a list posted on the site.

[911dark]

By thw way, the new tires/wheels have completly fixed the yaw stability issue. It's rock stable now at any speed.