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Discussion Starter #1
I recently "converted" my street/track '06 Cayman S back to street configuration and, among other things, raised my PSS9s 3 turns all around, set them on full soft, and reset camber and toe. Car tracks straight. I drove to Nashville from Memphis for Thanksgiving and thought it felt rough and like a bit of sway/roll in the back over one-sided bumps and even lane reflectors. There was a light rain most of the way back and it got downright scary. Over rough road, during lane changes on uneven pavement, and swales and rises in a construction zone it felt like the rear was going to break lose.

When I got home I checked the rear tires and they looked OK w/ plenty of tread. However, they are 5 1/2 year old Michelin Super Sports w/ 38,882 miles on them. They have remained on the car in an unheated garage through each winter. We have already had 4 days solid below freezing this Fall. Could it be that these tires have just lost their grip?
 

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The rubber could be getting a little hard; you've had them 5 1/2 years, but what's the production date code?

What was the temperature range for your drive from Nashville to Memphis? If you're driving below 45-degrees you might be expecting too much from your PSS summer tires. If you got almost 39,000 miles out of them, that's at least twice what I got out of my PSS's on my 981 Boxster. It's probably time for something new, like Pilot Sport 4S's.

Since you store your car in the winter, you might consider using Race Ramps Flat Stoppers to keep theyour new tires more round(https://www.raceramps.com/car-storage/ramps/flatstoppers/p/RR-FS-10/?gclid=EAIaIQobChMIso2a0vaS5gIVhONkCh2P2QghEAQYAyABEgJgfPD_BwE).
I store my Boxster for three to five months in the winter and the Flat Stoppers make for a smoother ride when I drive on the occasional warm & dry day.

Your story reminds me of a time Memphis when I kept OEM tires on my Mazda MX-6 for way too long. It was an "airport car" and the tires were almost 11 years old. One rainy day I started to the airport and noticed some slippage; I didn't realize at that time how old the tires were, but thought that I should probably get them replaced when I returned. I didn't make it to the airport before I spun the car in a decreasing right-hander and slammed the left rear into a curb. Anyway, after replacing some bent suspension components, wheel hub, and new tires I was back in business. Glad I didn't hit anyone or damage anyone else's property. Lesson learned: replace the tires at production code date plus 5-6 years.
 

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whoa...how did you make your PSS last so long? based on my experience in a tropical summer climate, PSS can get hard after about 3 years and about 40k kilometres - you'll feel the car understeer as it struggles to grip.
 

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Discussion Starter #4
Man, FlyerHiker, you opened a can of worms! Since I track this car I keep a diary, so to speak, of everything about it. But checking the date on these tires did not add up, as it was June 2015 and my record showed they were installed in May 2014. So I went through my bookkeeping records and found another pair of rears bought in Nov. 2015. I vaguely recall my toe being way off and ruining that earlier pair. I can find no record of mounting these (?) but estimate the mileage on them as a little over 22,000. So that means they are 4 1/2 years old.
Driving to and from Nashville the temp was always above 45.
The car is driven year round.
I had to replace the fronts on a sort of emergency basis and went w/ Continental ExtremeContact all seasons. I'll replace the PSSs w/ those.
Do you live in Memphis now?

Eyeofthetiger, this update should answer your question.

So, do I need new tires?
 

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If you're running Michelin PSS on the rear, with a reported 22,000 miles and all season Continentals on the front, the car will have unpredictable handling. Porsche insists on having the same manufacturer tires and tread patterns on both the front and rear. It's been reported time and again that mixing and matching tire makes/tread designs does NOT work well regarding how these cars handle. Not something I would even consider. This isn't a Toyota after all.
 

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Sorry about the can of worms, bldn10; I was just amazed at your reported mileage and I wondered how old the tires really were. As Budman mentioned, it's not good to mix brands of tires, especially mixing summer tires on the rear and all-seasons on the front. Your plan of replacing the rear PSS with the Continental's is a great place to start (assuming you've still got plenty of front tire tread.)

When my PSS's wore out on a 12-week (17,000 mile) road trip the new Pilot Sport 4S's weren't available in the 19's yet, so I went with the Continental Extreme Contact Sport. They don't have as stiff a sidewall as the Michelin's, but I'm satisfied with them for street use. I left the Memphis area (Germantown) in 2006, and I'm now in northern Nevada in the mountains (Lake Tahoe). If I keep the Boxster long-term I might try going with the Michelin Pilot Sport A/S 3+ in a slightly larger size front & rear, since they're not available in the OEM size front/rear. That would allow me to drive when it's cold (but not on snow/ice) later in the Fall and earlier in the Spring. I'd give up some dry cornering ability, but I'd get more days driving per year. I don't have enough garage storage space for two sets of wheels/tires to do the Summer/Winter setup.

You've got a lot more experience that I do on setting the suspension, but that would be my next step if you still have issues. For my long road trips with full luggage and two occupants, the front toe would change a fair amount from the "normal" driver and half-tank of gas setup. I had the toe adjusted for about half of the luggage/passenger weight and it seemed to help with the front tire wear and still corner pretty well.

Good luck and let us know your progress in solving your Twitchy Handling issue!
 

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Discussion Starter #7
I do all my aggressive driving on the track so the uneven handling has not been an issue for me in the 3 years I've had the mixed tires. I could see that in rain, sleet, and snow the Contis would have more grip than the PSS's, but the latter should have reasonable grip nevertheless. So, now that I have corrected the mileage and age of the PSS's [22,000 miles and 4 1/2 years], is it logical to conclude that they are no longer safe in bad weather?

FlyerHiker, would you be retired from FedEx? I have an old SCCA racing buddy in Reno who races a Datsun 260Z and flies an MD11.
 

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Yes, bldn10, I retired from FedEx as an MD-11 Captain in the LAX base, where I was the last five years before I retired.

I'm not qualified to say whether your tire combination is safe, but since you mentioned the twitchy handling I'm thinking that would be the place to start. Just the difference in the way all-seasons vs. summer tires deal with cold temperatures would make me nervous; maybe on the track where you are comfortable with whatever understeer/oversteer bias your setup gives you would work for you. On the street or especially on a road trip where you don't know the turns (like on Tail of the Dragon, Blue Ridge Parkway, etc.) I wouldn't want to be fighting the tire setup while I'm trying to have fun. Your mileage may vary ;-)
 

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Let us know how it is after you assumingly the PSS with rears matching Conti A/S
 

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Discussion Starter #10
Oh, no, I don't run street tires on the track; if I did we wouldn't be having this conversation because they would have been replaced many times over! On the track I use Hoosier R7s or take-off Pirelli slicks.

We got off on the rain handling, but as I mentioned, at 50+* in the dry the rear still felt funny. Even crossing a reflector it felt like the body rocked. Stock sway bars BTW. It's supposed to be close to 60* Thurs. so I'll take it out on the highway and concentrate on what's happening when and where.
 

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I would have your alignment rechecked (assume you did this after changing your coil-overs). I do have an extra set of wheels and tires (in Birmingham) if you would like to borrow them for an afternoon to see if it's the tires
 

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Discussion Starter #12
Thanks for the offer DMN987S but I have a set of track wheels/tires. That is a good idea, though.
Do I know you? I run most PCA D.E.s at Barber;I have the dark blue Cayman w/ red wheels.
265856
 

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What is the date code on the rears? I saw your update to the install and mileage numbers but who knows how long they were sitting before you got them.
 

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Discussion Starter #15
"checking the date on these tires did not add up, as it was June 2015"
"So that means they are 4 1/2 years old."
"mileage and age of the PSS's [22,000 miles and 4 1/2 years]"

2415
 

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My experience is that most of these performance tires "fall off a cliff" at some point before the tread is gone, though I did not experience that with my MIchelin PSS's. A few years ago my 981 had a twitchy rear end - I took it back to the shop and they found a loose nut or bolt in the suspension, re-aligned the car and it was fine. I found another shop.
 
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