Detachable Hardtops
Before the mid-1920s, 90% of automobiles had open tops, with rudimentary (if any) weather protection provided by a convertible-type canvas top and celluloid or isinglass side curtains. Some automobile bodies had roofs that could be removed during the summer and reattached during the winter, although it was a cumbersome and laborious job. By the time of World War I some automakers offered a lift-off roof, typically with a wood frame, canvas or leather covering, and glass windows. These removable roofs, sometimes called a California top, were the forerunners of the detachable hardtop, offering security and weather protection comparable to a fixed-roof model when installed.
Following the ascendancy of steel tops for closed bodies in the 1930s, detachable hardtops with metal roofs began to appear. After World War II, the availability of new types of plastic and fiberglass allowed lighter, easier to handle hardtops with much of the strength of a metal top.
In the 1950s and 1960s detachable hardtops were offered for various convertible sports cars and roadsters, including the 1955-1957 Ford Thunderbird and the Chevrolet Corvette. Because the convertible top mechanism is itself expensive, the hardtop was customarily offered as an additional, extra-cost option. On early Thunderbirds (and Corvettes through 1967), buyers could choose between a detachable hardtop and a folding canvas top at no additional cost, but paid extra for both.
Improvements in canvas tops have rendered the detachable hardtop less common in recent years, in part because the top cannot be stored in the vehicle when not in use, requiring a garage or other storage facility. Nonetheless, some open cars continue to offer it as an option. Around 10% of Mazda MX-5s are believed to have been delivered with an accessory hardtop, which is compulsory for some auto racing series.
Read more about this topic: Hardtop