The Mark VII was originally equipped with either Goodyear Eagle GA or Michelin MXV4 Energy tires. The size was P225/60 R16. The specific designation for the stock Goodyear GA tire was P225/60 R16 97V. All the stock wheels, no matter what the style, were 16 inch diameter 7 inch wide.
The cars are designed for the stock tires. In fact most new cars like the Mark VIII are designed from the ground up for a certain brand and type of tire. The suspension is tuned for that specific tire. The tire that is on the Mark VIII is a Goodyear Eagle GA specifically designed for the Mark VIII. It differs from the Eagle GA on the Lexus SC400 and from the generic Eagle GA sold in most tire shops.
You can put on a lower profile tire, and get better steering response and handling because sidewall flex is reduced. You lose some of the softness in the ride though. Your speedometer will be off because of the reduced diameter of the tire. If the profile is very low you also at greater risk denting the rim on bumps and potholes than with high profile tires. Tires slightly wider than stock can work, but this is mainly for aesthetics. The contact patch is not increased significantly enough to affect traction or performance. Handling may actually suffer due to increased sidewall flex. Stock tires are the best compromise for handling and ride.
Board user Mark Beyer called Goodyear to seek additional information that might interest others here on the LOD site. It was confirmed that Goodyear made a GA tire exclusively for the Mark VIII. That tire is slightly different from any other Goodyear GA. The Goodyear representative also confirmed that the car is designed for these GA tires and changing them may result in "handling issues". According to the rep, this meant that the car will likely handle differently when the tires are replaced. He would not, however, say that "different" necessarily meant worse. But....if a buyer wants to replace the OEM tires and maintain exactly what Lincoln intended, the "real GA's" are not available. Even those sold by the Lincoln Mercury dealer are only the generic GA's that can be purchased from any authorized Goodyear dealer (and probably for less money).
Alexander Sosiak & Mark Beyer