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Discussion Starter · #1 · (Edited)
Hi - I've been putting a summer/track wheels+tires combo together:

used 996 turbo twist wheels, 8" and 11" widths, front and rear,
used pirelli P-zero fronts - I think they've sat a year or more, -- 225/40-18s
new Sumitomo HTRZ-II rears (Tirerack.com has great prices on these) - 275/35-18.

the 11" rear wheels have an offset of 45 - so I found a used set of 15mm spacers and use these w/ the rear wheels + tires. They fit w/o rubbing but it's tight.

using 5mm spacers on the front.

both the fronts and rears are summer / high-performance tires. I had been using all seasons in 235, 265 / 40 - 18" sizes.

So. First drive and the new setup is twitchy, really twitchy and I could use some learned opinions as to what may be going on. The rear seems well planted, and the front responds immediately to even the smallest input - sometimes to a too-great degree.

At speed I had to back off because my corrections for wind, road were only tossing the car worse than what I was trying to correct for. up to now the cayman was very easy to drive fast.

my pet theories -

1) the fronts came w/ the wheels and seemed pretty hard. maybe they need some recent miles to soften up. dropping the pressures to 35 -warm seemed to help.

2) the rears are new and not broken in at all ... probably started this drive on whatever the tires come coated in from manufacturing. That said, the problem seems more front than rear.

3) taking some sweepers at speed, PSM would activate briefly - I have a good match on tire diameters front to back, wonder if the rear's wider track may be fooling the PSM.

4) maybe I am just sticking that much more ... but I still couldn't drive smooth enough at speed w/o the car starting to hunt back and forth.

5) maybe one of the used fronts is separating or has some other serious problem.


Thoughts?

the first thing I'm going to do tomorrow is put my all-season fronts back on and see how it feels. If there's a significant improvement then I'll probably have to pop for 2 more new tires.

thanks,

-PM
 

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I can only comment really on 1 & 2.

1: Check the dot number for the manufacturing date. Tires get hard over time from the rubber compound oxydising.

2: New tires come with mold release since they are new. I normally get rid of it in 35 to 50 miles. It can be slippery.
 

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What are your alignment specs? - any toe out on the fronts would give some of the characteristics you describe.

Not sure what you mean by "35 warm" regarding the front pressures, but unless that's a hot pressure, it seems a little high for a front tire that is a bit skinnier than than the OEM (recommended front cold pressure is 29).

I doubt that the slightly wider rear track is causing the PSM activation.

My :2cents:
 

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Discussion Starter · #4 ·
Thanks for the replies -

I'll check the manufacture date for the fronts - good idea, that.

35 psi warm meant 35psi hot. I started w/ 32 cold, and found the fronts to be @ 40psi hot. I then dropped them to 35 hot which seemed to help.

As I said, today I'll put the all-season fronts on which I'm used to -- if the problem goes away, it's the front tires which came w/ the wheels. if not, the rears probably need some scrubbing.
 

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Discussion Starter · #5 ·
update - the manufacture date code ends in 1303 - 13th week of 2003 ... these tires are 7 years old.

any chance they'll soften up or should I just pop for 2 new ones ??
 

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Discussion Starter · #6 ·
update - the manufacture date code ends in 1303 - 13th week of 2003 ... these tires are 7 years old.

any chance they'll soften up or should I just pop for 2 new ones ??

Update: I ordered 2 new htrz-IIs to match the 2 new rear tires; and I took a drive w/ my current all-seasons on the front ... problem gone.

either it's the Pirelli P-zero tires - maybe one separating - or I have a cracked wheel.

I doubt a turbo-twist wheel could get hammered enough to crack w/o showing serious damage ... I'll power-wash them this weekend and take a close look.
 
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