In addition to lowered suspension, I had to readjust my tire pressures to suit the new suspension. Never have I been in a car where a few psi made so much of a difference before

 

Adjusted, how?

 

I had to deviate from the factory recommended air pressure settings and experiment with different tire pressures to get a more stable handling car afterwards. For example anywhere from 38-40 rear psi was way to high for my setup and I found the rear really nervous when cornering or hitting bumps mid corner. For me there was a BIG difference setting it at 40 vs 37, even though it was only a 3 psi difference.

 

I remember reading about factory tire pressure for a single driver, vs. a family of 4 - with the single driver pressures WAY lower. Does lower pressure mean more stability, less squirrely behavior?

 

I was worried my new-to-me 40th anniversary edition with 8k had something wrong... very front end floaty at highway speed... mostly self correcting, which I attributed to massive rear tires, lots of rear end down force and a light weight front end...

So loweing is really all I'm hearing will eliminate this (which I don't want to do if possible)? Maybe tire pressure changes, maybe alignment...

It is an unnerving sensation really... I'd like to fix if possible

 

Just try out experimenting with different tire pressures. It's cheap(or free) and easy.

Also not everyone's driving style/skill/comfort are the same so find one that suits you best.

If tire pressure adjustments don't work, then go after the bigger ticket items afterwards.

 

I saw the 997 TSB that says for HALF load (driver plus one, no heavy luggage), the recommended pressures are 33f / 36r.

I'm going to try these and see if the tracking becomes more stable.

 

My '02 Cab feels rock solid on 18"/PS2's -- but "floaty" when I switch to my winter 17"/Blizzaks.

The car should feel solid with the correct tires & alignment to that wheel/tire combination.

 

Although you have made several Non-Porsche approved alterations to your Porsche I believe the tires are the main problem.

Are the rear wheels 10" wide with 65mm offset? Marked on outside rim if OEM
What tire size & model & brand are you running front & rear? size= ---/--/18

 

This is a new problem, I am running general ump 235/35/19 front, new tires are one size larger,Hankook v12's rear, 285/30/19 on a 10" rim. the tread patterns are very similar both v looking directional. One thing I have never done is run 45psi in rear before, always 34. the car tracked very well. I just lowered the rear psi to 42 and it seemed a little better,going to lower to 38. I will check back in. Also going in for suspension check Monday to correct clunk sound which I believe might be upper strut mounts, will get an alliginment while there and have them check ball joints,sway bar bushings etc.

 

Mine is sitting at GT3 ride height so the comparison may not be viable, but it is very stable at highway speed and above. I'm running Michelin PS2's (235/40-18, 295/30-18) with 36 lbs front and 44 rear. The only time it feels floaty is under hard acceleration in the peak torque range and all that rearward weight transfer is going on. Under more steady state conditions it feels nicely planted. I too would suggest the mismatched front and rear tires as the first variable to eliminate. Even if the tread patterns look similar there are a ton of other design and construction elements that influence how mismatched tires interact with each other.

 

Took mine up to 115 last weekend .. felt totally planted ... stock suspension ...i ve noticed float at lower speeds ..perhaps that's your problem driving too slow ?

 

Lowered psi to 38 in rear from 45 and the car felt heavy again. No twitchy feeling or disconnect. I will get dealer investigation work done and report on front clunk. Thx for all input.

 

Just got car out of shop for clunk sound, serv. rep told warranty co. I needed sway bar links and trailing arms. I paid for allignment. Car definetly tighter and with reduced tire psi 34/38 the wandering has stopped. Funny thing drove over the uneven pavement where it always clunks and it clunked but not as loud. He said I didn't need upper strut mounts. Go back in a few months for oil change and say it still clunks, maybe I'll get something else under warranty. Warranty bill $1k. Hope this helps someone.

 

using better tires help -> PS2 michelin
using lower profile tire helps as well -> 19" wheels
Our cars are 10 years old, all the suspension bushing are more flexible if not dead. To regain the initial stability all of those need to be updated. There are not that many afterall.

My car which drove great on lower suspension PSS9 and PS2, but still he insisted for me to upgrade all my bushing and I would thank him. I did not do so and I think the car rides well, but certainly the bushing upgrade would make sense. It is just that you need to remove all part then bring them to the shop so they an press the bushing in the arms.

I am surprised nobody has posted any DIY on the forum about this process.

most of us use the firmer suspension and that fixes it I guess.