This side entry demi-tonneau shows where the high rounded back styling made these cars look like touring cars. The rear passenger compartment and windshield could be removed for a sportier roadster look. Photo from keysorautomobileworks.com.

A Tonneau car was simply an early style automobile with an open rear passenger compartment that was typically rounded in a barrel shape, usually with high sides. Tonneau is the French word for “cask.” Tonneau automobiles started with rear facing hinged doors which evolved into side entry doors in later versions. True tonneau cars had the tonneau covers fixed in place.

Unlike the tonneau cars, demi-tonneau automobiles featured a convertible body in which the tonneau and rear rumble seats could be removed. These were essentially an early automobile that was an open runabout with a detachable and removable rear passenger section. The removable rear passenger section added passenger capacity beyond the normal two seat runabout or speedster. This quickly turned a touring car into a roadster, making the demi-tonneau two cars for the price of one.

1910 Buick demi-tonneau. Photo from wikipedia.com.

Once the rear section and windshield was removed, the owner was rewarded with a nice speedster that could travel around the countryside with sporty intent. If adding a couple of passenger seats was desired, the car could be converted back to a touring car in less than an hour. Definitely a remarkable feat for those times.

The early demi-tonneau autos featured a hinged rear entry door. Photo from wikipedia.com.

Unlike runabouts or roadsters, the tonneau and demi-tonneau cars did not have a gas tank or trunk in the rear. The passenger seats having priority for space in the rear. The gas tank was most often located under the front seat in these models.