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      11-25-2012, 01:33 PM   #13
smmmurf
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Drives: 2009 M3 Sedan 6MT
Join Date: Feb 2008
Location: Pleasanton, CA

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Quote:
Originally Posted by mlhj83 View Post
First of all, do not mix PSS and PS2 (or any other brand for that matter), as the different grip and roll characteristics of different front and roll tyres causes an imbalance in handling. I experienced this first hand when I fitted PSS (oem size) to the rear only to see how handling changed.

Upsizing the rears only will have more effects than just increasing the tendency for understeer at the limit; you may also increase oversteer in the wet as the wider rear tyres are more prone to aquaplaning. Not only that, the car will also be raised slightly at the rear due to the increased height of the tyre sidewall, and the roll characteristic of the rear will also be changed due to an increase in rear track width. These changes will undoubtedly affect handling balance. Therefore, if you want to upsize, do it proportionally.
The above poster makes some good points; however in my experience with both tires, the PSS has significantly more grip than the PS2 in the wet making the PSS with full tread depth more grippy and capable in the wet in all conditions than the standard sized PS2 even if upsized to the 275 size. The bigger difference is the large change in traction characteristics from the PSS's new compound and tire construction.

As the previous poster stated, the roll difference is significant. The PS2 does not generate as much lateral grip as the PSS. It will make for a very wonky handling car at the limit. The fronts will not be able to generate enough grip and the car will understeer significantly more than with matched PS2's. I have tried the two different kinds of tires on my own car and found this result. Even with full PSS in stock sizes, the car rolls more with the additional grip (given nothing else in the suspension changed such as camber, spring rates, toe settings-- the whole car has more grip and it takes more throttle to get the rear tires to break traction).

But, like other posters say, if you never track the car or drive with MDM on/DSC off the difference will not be very large.

In principle, though, I would run matching front and rears. Another 11K miles is a long time to drive with mismatched tires. I bought this car for the way the whole package behaves under all conditions and if my car handled funky when pushed hard it would annoy me greatly.

Go full PS2 or full PSS. Both are incredibly good tires (even PS2 still).
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