The load capacity coefficient (e.g. "91") and maximum speed code letter (e.g. "Y") are minimum requirements.
Improper Tire Size
Installation of sizes not authorized by Porsche may impair driving stability and could result in loss of control of the vehicle.
Tire and rim sizes
Extensive tests are performed before specific tires and wheels are approved by Porsche. Your Porsche dealer has information about approved tires and wheels and is happy to assist you. If aftermarket tires and/or wheels are installed which are not approved by Porsche, the vehicle's roadability and handling characteristics might be impaired. Since Porsche has no data on such combinations, Porsche cannot stand behind the safety or durability of these aftermarket combinations.
Can be mounted only on the rear wheels; maximum speed 30 mph/50 km/h. Use only Porsche authorized fine-link cross-type or edge chains. Snow chain clearance can be guaranteed only with the tire + rim combination marked* without spacers. Please see the chapter “SPACERS” on page 211.