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Old 11-06-2005, 01:58 PM   #2
TriGem2k
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Quote:
Originally Posted by mjw930
I've been fighting a problem with a set of PS2's (non N-Spec) on my Boxster S. The biggest problem manifests itself as a high speed shimmy (vibration) at 70mph+. It doesn't get a lot worse as the speed increases but it will travel through the entire car. I have had the 2 fronts replaced under warranty and it helped but didn't clear the problem.

As strange as it may sound I think the very soft sidewall of the non-Porsche spec PS2's combined with the relative stiffness of the Boxster and the Boxster's inherent drop top flex sets up a sympathetic vibration in this tire/size combo. I've had the wheels checked for true, the road force comes in at single digits and it's literally balanced to .05 oz on the top of the line Hunter 9700 machine (calibrated just before we put my wheels on it).

For reference the combination is Kinesis K18R's in the proper Boxster 18x8.5 and 18x9.5 size. The tires are 225/40x18 and 265/35x18 PS2's (not N-Spec)

Another thing I dislike about this combo is the effect it's had on the handling. Even though the car generated extremely good corner force the feel and turn-in are quite sloppy. The slip angle on these tires makes the rear twitchy and the front sloppy. On top of that the tramlining borders on dangerous. Not what I expected after my previous experience with the PS2's on other cars. Having felt the N-Spec PS2's on a 911 I'm becoming a believer that there is an internal difference between the N-Spec and non N-Spec tires of the same brand.

I may be going to either the N spec Pilot Sport Ribs or some other brand real soon. I want the best performance I can get and I spent top dollar on the best stuff I could find, Kinesis K18R's and Michelin PS2's. I'm quite upset that $5000 later the car rides and handles worse than it did with worn AVS sports on Mille Miglia replica 17's

Thoughts?
THe PS2 Tire in General is a soft tire regardless of the N Spec or not. It is more of a comfort tire
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