For the 1957 model year, the Imperial received its own platform, setting it apart from any other division of Chrysler. This would last through the 1966 model year. Imperials during this period were substantially wider, both inside and out, than other Mopars, with front and rear shoulder room equal to and respectively. The front seat shoulder room measurement remains an unsurpassed record for Imperial and would remain the record for any car until the 1971–1976 GM full-size models. Exterior width reached a maximum of for 1961–1963, which remains the record for the widest non-limousine American car. After Lincoln downsized for 1961, this generation of Imperial had no real competitor for the title of largest car for the remainder of its decade-long lifespan.