Ford Explorer parts have changed a lot since it was introduced in the early 1990s. It has gone from a direct descendant of the rough Ranger/Bronco II to a modern car-based unibody. Beam axles have becomes multilink independent suspensions, pushrod V6s have become DOHC multivalve engines, and the body-on-frame construction has become a unibody. The Explorer became embroiled in a rollover controversy due to its high center of gravity and tread separation of its Firestone tires. The Explorer was also marketed as the Mazda Navajo and Mercury Mountaineer. Even though today's Explorer is almost unrecognizable next to the original, the model has always offered the utility of an SUV with the rugged good looks of a modern truck.