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      03-03-2010, 01:26 AM   #9
SF-M3
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Drives: E90 M3
Join Date: Feb 2009
Location: SF. CA

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No real need to by from the dealer, however getting the correct spec PS2 will improve the ride/handling of the car.

No all PS2 are created equal. See specs below pulled from Tire Rack. My guess is the extra load rating is a result of stiffer side wall.

245/40ZR18 (93Y) SL BMW 220 AA A 1433 lbs.

245/40ZR18 (97Y) XL AO (Audi) 220 AA A 1609 lbs.

I know when purchasing off road tires for my land rover, Going with the lowest load capacity tire (while still being higher than the Max GVW) results in a much smoother ride off highway. Basically extra flexibility in the tire adds to the overall suspension of the truck.