straight line stability - 986 Forum - The Community for Porsche Boxster & Cayman Owners

jaykay · 09-21-2009, 06:22 PM

I find my the straight line stability of my 2000 S (18" 3 piece sport classics) pretty twitchy when there are disturbances, longitudintal (with the direction of travel) undulations in the pavement.

I seem to recall later model years going through changes in the rear track bars to attack this problem. Has any one fitted later model reat track bars with a good effect?

I had 15mm F and 23mm R wheel spacers on which made the car much more sure footed; perhaps they gave a favorable roll centre change; track change. I had to take them off as I was getting substantial vibrations in the steering and the seat from 110kph to 130kph+. There may a balance/manufacturing problem with them...not sure yet.

ekam · 09-21-2009, 07:01 PM

Quote:

Originally Posted by jaykay

I find my the straight line stability of my 2000 S (18" 3 piece sport classics) pretty twitchy when there are disturbances, longitudintal (with the direction of travel) undulations in the pavement.

I seem to recall later model years going through changes in the rear track bars to attack this problem. Has any one fitted later model reat track bars with a good effect?

Did you get a mechanic to check for worn out suspension parts?

Quote:

Originally Posted by jaykay

I had 15mm F and 23mm R wheel spacers on which made the car much more sure footed; perhaps they gave a favorable roll centre change; track change. I had to take them off as I was getting substantial vibrations in the steering and the seat from 110kph to 130kph+. There may a balance/manufacturing problem with them...not sure yet.

That means your spacers are not hub centric.

jaykay · 09-21-2009, 07:09 PM

the car has very low mileage; I did have the front track bars changed as the bushing had degraded over time........I assume that everything was checked but I will check the rear for worn items again

thanks for your help

jaykay · 09-21-2009, 07:13 PM

the spacers were H+R and Eib....high quality centric ones but perhaps they have a machining error somewhere....

Topless · 09-21-2009, 08:54 PM

Maybe just tires or alignment issues. My car is 11 yrs old with 82k miles and feels just as calm and stable at 120mph as it does at 40. Surprising really. Visually inspect the front suspension for damage or loose bushings and then have someone who knows these cars test drive it.

sd_boxster · 09-21-2009, 10:21 PM

Not entirely sure I understand the symptom you're describing. The P Zero Rossos that my '03 was equipped with when I bought it would track every line and rut in the road.

Changing the tires (in my case to Yokohama S.Drive) eliminated that nasty habit.

jaykay · 09-22-2009, 03:04 PM

yes that is part of it ........but there is also a slight wander/dancing on the smooth surface as well even after an alignment...seems to be an early 986 thing where as later rear track bars were changed to solve this.

spacers gave me huge vibrations...???

RandallNeighbour · 09-22-2009, 03:11 PM

spacers will always accentuate any inherent wheel imbalance, even if they're totally round and true.

jaykay · 09-22-2009, 04:03 PM

yes very true......tried that but the balance was fine perhaps I will have to try again..

turbo23dog · 09-22-2009, 04:10 PM

At the risk of stating the obvious, are you sure that the tires are inflated to the recommended PSI? I've seen an under inflated tire on one side cause this on several different cars i've owned.

jaykay · 09-22-2009, 04:32 PM

very good point; yes low profiles are really sensitive to this; they were okay as checked with my gauge...but I will try another

the spacer vibration was quite violent and 110; 130kph so this seem to point to a problem with them rather than a tire pressure differential.

to further complicate this thread I did have a lower rear stress bar put on at the same time!!!?