Hot ros are typically American cars with large engines modified for linear speed. Nobody knows for sure the origin of the term "hot rod." One explanation is that the term is a contraction of "hot roadster," meaning a roadster that was modified for speed. Open roadsters were the cars of choice to modify because they were light. Hot Rod may also refer to the connecting rods, cam, or pushrods inside the engine or to the exposed frame rails of such an automobile. It has also been noted that burning out the connecting rod bearings was a very common failure mode for souped up four-cylinder Fords, particularly the Model T, and "hot rod" could refer to that phenomenon. It was adopted in the 1930s or 1940s as the name of a car that had been "hopped up" by modifying the engine in various ways to achieve higher performance.