The Benz Patent-Motorwagen ("patent motorcar"), built in 1885 by the German Carl Benz, is widely regarded as the world's first practical modern automobile and was the first car put into series production. It was patented and unveiled in 1886. The original cost of the vehicle in 1886 was 600 imperial German marks, approximately 150 US dollars (). Karl's wife Bertha demonstrated its feasibility in a trip from Mannheim to Pforzheim in August 1888, shortly before it became the first commercially available automobile in history in the late summer of 1888. Due to the creation of the Patent-Motorwagen, Benz has been hailed as the father and inventor of the automobile. Development and specifications After developing a successful gasoline-powered two-stroke piston engine in 1873, Benz focused on developing a motorized vehicle while maintaining a career as a designer and manufacturer of stationary engines and their associated parts. The Benz Patent-Motorwagen was a motor tricycle with a rear-mounted engine. The vehicle contained many new inventions. It was constructed of steel tubing with woodwork panels. The steel-spoked wheels and solid rubber tires were Benz's own design. Steering was by way of a toothed rack that pivoted the unsprung front wheel. Fully elliptic springs were used at the back along with a beam axle and chain drive on both sides. A simple belt system served as a single-speed transmission, varying torque between an open disc and drive disc. The first Motorwagen used the Benz single-cylinder four-stroke engine with trembler coil ignition. This new engine produced at 250 rpm in the Patent-Motorwagen, although later tests by the University of Mannheim showed it to be capable of at 400 rpm. It was an extremely light engine for the time, weighing about . Although its open crankcase and drip oiling system would be alien to a modern mechanic, its use of a pushrod-operated poppet valve for exhaust would be quite familiar. A large horizontal flywheel stabilized the single-cylinder engine's power output. An evaporative carburettor was controlled by a sleeve valve to regulate power and engine speed. The first model of the Motorwagen had not been built with a carburettor, rather a basin of fuel soaked fibers that supplied fuel to the cylinder by evaporation. The vehicle was awarded the German patent number 37435, for which Karl Benz applied on 29 January 1886. Following official procedures, the date of the application became the patent date for the invention once